《第一行代码》学习笔记

基于《第一行代码》第二版

应用抽屉中显示的名称通常是 AndroidManifest.xml 文件中 <application> 标签的 android:label 定义的值。但如果在应用程序的 入口 Activity（具有 MAIN 和 LAUNCHER 的 intent-filter）中定义了 android:label，则该值会覆盖 <application> 的 android:label，并显示在应用抽屉中。
Switch-case的case后只能放常亮不能放变量
1
android:id="@+id/add_item"

以上创建的id是一个变量

四种布局

LinearLayout：

1
2
3

android:orientation排列方向
android:layout_gravity单个组件排列方向的另一方向
android:layout_weight比例布局(需要把orientation方向的高或宽置零)

RelativeLayout

android:layout_alignParentTop
android:layout_centerInParent
android:layout_above某一个组件
android:layout_toLeftOf某一个组件
android:layout_alignLeft某个组件 多组件指定边缘对齐

FrameLayout
1
android:layout_gravity

帧布局

add dependency

1	`implementation "androidx.percentlayout:percentlayout:1.0.0"`

有PercentFrameLayout和PercentRelativeLayout两种

以前者为例：

<androidx.percentlayout.widget.PercentFrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/button1"
        android:text="Button 1"
        android:layout_gravity="left|top"
        app:layout_widthPercent="50%"
        app:layout_heightPercent="50%"/>

</androidx.percentlayout.widget.PercentFrameLayout>

自定义布局

android:gravity=”center”是对textView中文字居中

android:layout_gravity=”center”是对textview控件在整个布局中居中

在别的xml中使用：

1	`<include layout="@layout/title"/>`

自定义控件：

public class TitleLayout extends LinearLayout {

    public TitleLayout(Context context, AttributeSet attrs){
        super(context,attrs);
        LayoutInflater.from(context).inflate(R.layout.title,this);
        Button button1 = (Button) findViewById(R.id.title_back);
        Button button2 = (Button) findViewById(R.id.title_edit);
        button1.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                ((Activity)getContext()).finish();
            }
        });
        button2.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(getContext(),"You clicked Edit button",Toast.LENGTH_SHORT).show();
            }
        });
    }
}

ListView控件：

定义实体类：

public class Fruit {
    private String name;
    private int imageId;

    public Fruit(String name,int imageId){
        this.imageId=imageId;
        this.name = name;
    }

    public String getName(){
        return name;
    }

    public int getImageId(){
        return imageId;
    }
}

定义ListView的子项布局

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/fruit_image"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/fruit_name"
        android:layout_gravity="center"
        android:layout_marginLeft="10dp"/>

</LinearLayout>

定义Adapter

public class FruitAdapter extends ArrayAdapter<Fruit> {
    private int resourceId;

    public FruitAdapter(Context context, int textViewResourceId, List<Fruit> objects){
        super(context,textViewResourceId,objects);
        resourceId = textViewResourceId;
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        Fruit fruit = getItem(position);
        View view = LayoutInflater.from(getContext()).inflate(resourceId,parent,false);
        ImageView fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
        TextView fruitName = (TextView) view.findViewById(R.id.fruit_name);
        fruitImage.setImageResource(fruit.getImageId());
        fruitName.setText(fruit.getName());
        return view;
    }
}

在主程序调用

public class MainActivity extends AppCompatActivity {
  
    private List<Fruit> fruitList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //定制ListView
        initFruits();
        FruitAdapter adapter = new FruitAdapter(this,R.layout.fruit_item,fruitList);
        ListView listView = (ListView) findViewById(R.id.list_view);
        listView.setAdapter(adapter);

    }

    private void initFruits(){
        for(int i =0;i<2;i++){
            Fruit apple = new Fruit("Apple",R.mipmap.ic_launcher);
            fruitList.add(apple);
            Fruit banana = new Fruit("Banana",R.mipmap.ic_launcher);
            fruitList.add(banana);
            Fruit orange = new Fruit("Orange",R.mipmap.ic_launcher);
            fruitList.add(orange);
            Fruit watermelon = new Fruit("Watermelon",R.mipmap.ic_launcher);
            fruitList.add(watermelon);
            Fruit pear = new Fruit("Pear",R.mipmap.ic_launcher);
            fruitList.add(pear);
            Fruit grape = new Fruit("Grape",R.mipmap.ic_launcher);
            fruitList.add(grape);
            Fruit pineapple = new Fruit("Pineapple",R.mipmap.ic_launcher);
            fruitList.add(pineapple);
            Fruit strawberry = new Fruit("Strawberry",R.mipmap.ic_launcher);
            fruitList.add(strawberry);
            Fruit cherry = new Fruit("Cherry",R.mipmap.ic_launcher);
            fruitList.add(cherry);
            Fruit mango = new Fruit("Mango",R.mipmap.ic_launcher);
            fruitList.add(mango);
        }
    }
}

对Adaptor进行优化：

public class FruitAdapter extends ArrayAdapter<Fruit> {
  private int resourceId;

  public FruitAdapter(Context context, int textViewResourceId, List<Fruit> objects){
    super(context,textViewResourceId,objects);
    resourceId = textViewResourceId;
  }

  @NonNull
  @Override
  public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
    Fruit fruit = getItem(position);
    View view;
    ViewHolder viewHolder;
    if(convertView == null){
      view = LayoutInflater.from(getContext()).inflate(resourceId,parent,false);
      viewHolder = new ViewHolder();
      viewHolder.fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
      viewHolder.fruitName = (TextView) view.findViewById(R.id.fruit_name);
      view.setTag(viewHolder);
    }else{
      view = convertView;//convertView对之前加载好的布局进行缓存
      viewHolder = (ViewHolder) view.getTag();
    }

    viewHolder.fruitImage.setImageResource(fruit.getImageId());
    viewHolder.fruitName.setText(fruit.getName());
    return view;
  }

  class ViewHolder{
    ImageView fruitImage;
    TextView fruitName;
  }
}

点击列表item事件：

protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  //定制ListView
  initFruits();
  FruitAdapter adapter = new FruitAdapter(this,R.layout.fruit_item,fruitList);
  ListView listView = (ListView) findViewById(R.id.list_view);
  listView.setAdapter(adapter);
  listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
      Fruit fruit = fruitList.get(position);
      Toast.makeText(MainActivity.this,fruit.getName(),Toast.LENGTH_SHORT).show();
    }
  });
}

RecyclerView控件：

同样定义在了support库中，需要添加依赖

1	`implementation "androidx.recyclerview:recyclerview:1.3.2"`

在xml使用

<androidx.recyclerview.widget.RecyclerView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/recycler_view"/>

写Adaptor

package com.example.recyclerview;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import java.util.List;

public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder> {
  private List<Fruit> mFruitList;

  static class ViewHolder extends RecyclerView.ViewHolder{
    ImageView fruitImage;
    TextView fruitName;

    public ViewHolder(View view){
      super(view);
      fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
      fruitName = (TextView) view.findViewById(R.id.fruit_name);
    }
  }

  public FruitAdapter(List<Fruit> fruitList){
    mFruitList = fruitList;
  }

  @NonNull
  @Override
  public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item,parent,false);
    ViewHolder holder = new ViewHolder(view);
    return holder;
  }

  @Override
  public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
    Fruit fruit = mFruitList.get(position);
    holder.fruitImage.setImageResource(fruit.getImageId());
    holder.fruitName.setText(fruit.getName());
  }

  @Override
  public int getItemCount() {
    return mFruitList.size();
  }
}

使用

public class MainActivity extends AppCompatActivity {

  private List<Fruit> fruitList = new ArrayList<>();

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    initFruits();
    RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
    LinearLayoutManager layoutManager = new LinearLayoutManager(this);
    recyclerView.setLayoutManager(layoutManager);
    FruitAdapter adapter = new FruitAdapter(fruitList);
    recyclerView.setAdapter(adapter);

  }

  private void initFruits(){
    for(int i =0;i<2;i++){
      Fruit apple = new Fruit("Apple",R.mipmap.ic_launcher);
      fruitList.add(apple);
      Fruit banana = new Fruit("Banana",R.mipmap.ic_launcher);
      fruitList.add(banana);
      Fruit orange = new Fruit("Orange",R.mipmap.ic_launcher);
      fruitList.add(orange);
      Fruit watermelon = new Fruit("Watermelon",R.mipmap.ic_launcher);
      fruitList.add(watermelon);
      Fruit pear = new Fruit("Pear",R.mipmap.ic_launcher);
      fruitList.add(pear);
      Fruit grape = new Fruit("Grape",R.mipmap.ic_launcher);
      fruitList.add(grape);
      Fruit pineapple = new Fruit("Pineapple",R.mipmap.ic_launcher);
      fruitList.add(pineapple);
      Fruit strawberry = new Fruit("Strawberry",R.mipmap.ic_launcher);
      fruitList.add(strawberry);
      Fruit cherry = new Fruit("Cherry",R.mipmap.ic_launcher);
      fruitList.add(cherry);
      Fruit mango = new Fruit("Mango",R.mipmap.ic_launcher);
      fruitList.add(mango);
    }
  }
}

实现横向滚动和瀑布流布局：

在LayoutManager后配置：
1
layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);

其他布局（GridLayoutManager, StaggeredGridLayoutManager etc）

public class MainActivity extends AppCompatActivity {

    private List<Fruit> fruitList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initFruits();
        RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);
LinearLayoutManager(this);
        StaggeredGridLayoutManager layoutManager = new StaggeredGridLayoutManager(3,StaggeredGridLayoutManager.VERTICAL);
        recyclerView.setLayoutManager(layoutManager);
        FruitAdapter adapter = new FruitAdapter(fruitList);
        recyclerView.setAdapter(adapter);

    }
}

RecyclerView点击事件

public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder> {
    private List<Fruit> mFruitList;

    static class ViewHolder extends RecyclerView.ViewHolder{
        ImageView fruitImage;
        TextView fruitName;
        View fruitView;

        public ViewHolder(View view){
            super(view);
            fruitView = view;
            fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
            fruitName = (TextView) view.findViewById(R.id.fruit_name);
        }
    }

    public FruitAdapter(List<Fruit> fruitList){
        mFruitList = fruitList;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item,parent,false);
        ViewHolder holder = new ViewHolder(view);
        holder.fruitView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int position = holder.getAdapterPosition();
                Fruit fruit = mFruitList.get(position);
                Toast.makeText(parent.getContext(),"you clicked view "+fruit.getName(),Toast.LENGTH_SHORT).show();
            }
        });
        holder.fruitImage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int position = holder.getAdapterPosition();
                Fruit fruit = mFruitList.get(position);
                Toast.makeText(parent.getContext(),"you clicked image "+fruit.getName(),Toast.LENGTH_SHORT).show();
            }
        });
        return holder;
    }
...

一个实战案例

首先需要添加RecyclerView依赖库，然后编写主界面，主界面主要是一个滚动列表、一个文本框和一个send按键，这里嵌套了一个LinearLayout：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#d8e0e8">

    <androidx.recyclerview.widget.RecyclerView
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:id="@+id/msg_recycler_view"/>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <EditText
            android:id="@+id/input_text"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="Type something here"
            android:maxLines="2"/>

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/send"
            android:text="Send"/>
    </LinearLayout>

</LinearLayout>

然后建立消息实体类，消息包含两部分内容：消息体和消息来源：

public class Msg {
    public static final int TYPE_RECEIVED = 0;
    public static final int TYPE_SENT = 1;
    private String content;
    private int type;

    public Msg(String content,int type){
        this.content = content;
        this.type = type;
    }

    public String getContent(){
        return content;
    }

    public int getType(){
        return type;
    }
}

然后写RecyclerView子项的布局，子项有两部分：一个是发送方的文本框，一个是接收方的文本框，LinearLayout中嵌套两个LinearLayout，可以控制显示隐藏

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="10dp">
    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/left_layout"
        android:layout_gravity="left"
        android:background="@drawable/message_left">
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_margin="10dp"
            android:id="@+id/left_msg"
            android:textColor="#fff"/>

    </LinearLayout>

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/right_layout"
        android:layout_gravity="right"
        android:background="@drawable/message_right">
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:id="@+id/right_msg"
            android:layout_margin="10dp"/>

    </LinearLayout>

</LinearLayout>

编写RecyclerView的adapter MsgAdapter，创建私有消息列表；创建ViewHolder类继承RecyclerView.ViewHolder类并在class中重写ViewHolder，将RecyclerView子项布局中的子布局和文本都注册；写MsgAdapter的构造方法；重写onCreateViewHolder，创建view为子类布局，将子布局的xml_id注入，返回ViewHolder(view) ；重写onBindViewHolder，得到当前位置，得到对应信息，根据信息来源将holder中内容配置可见或GONE以及文本内容；重写getItemCount。

public class MsgAdapter extends RecyclerView.Adapter<MsgAdapter.ViewHolder>{

    private List<Msg> mMsglList;
    static class ViewHolder extends RecyclerView.ViewHolder{
        LinearLayout leftLayout;
        LinearLayout rightLayout;
        TextView leftMsg;
        TextView rightMsg;
        public ViewHolder(View view){
            super(view);//kankan super shisha
            leftLayout = (LinearLayout) view.findViewById(R.id.left_layout);
            rightLayout = (LinearLayout) view.findViewById(R.id.right_layout);
            leftMsg = (TextView) view.findViewById(R.id.left_msg);
            rightMsg = (TextView) view.findViewById(R.id.right_msg);
        }
    }


    public MsgAdapter(List<Msg> msglist){
        mMsglList = msglist;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.msg_item,parent,false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Msg msg = mMsglList.get(position);
        if(msg.getType()==Msg.TYPE_RECEIVED){
            holder.leftLayout.setVisibility(View.VISIBLE);
            holder.rightLayout.setVisibility(View.GONE);
            holder.leftMsg.setText(msg.getContent());
        }else if(msg.getType()==Msg.TYPE_SENT){
            holder.leftLayout.setVisibility(View.GONE);
            holder.rightLayout.setVisibility(View.VISIBLE);
            holder.rightMsg.setText(msg.getContent());
        }
    }

    @Override
    public int getItemCount() {
        return mMsglList.size();
    }
}

编写MainActivity，初始化消息列表；将输入文本框、按键和滑动列表分别对应到布局id，然后建立LinearLayoutManager并注入滑动列表，new出来适配器也注入滑动列表；然后设计了一个send按键的响应：获取输入文本框内容，将内容new成消息，将消息添加到消息列表，设置刷新滑动列表，设置定位到最后一行，清空输入文本框。

public class MainActivity extends AppCompatActivity {
    private List<Msg> msgList = new ArrayList<>();
    private EditText inputText;
    private Button send;
    private RecyclerView msgRecyclerView;
    private MsgAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initMsgs();
        inputText = (EditText) findViewById(R.id.input_text);
        send = (Button) findViewById(R.id.send);
        msgRecyclerView = (RecyclerView) findViewById(R.id.msg_recycler_view);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        msgRecyclerView.setLayoutManager(layoutManager);
        adapter = new MsgAdapter(msgList);
        msgRecyclerView.setAdapter(adapter);
        send.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String content = inputText.getText().toString();
                if(!"".equals(content)){
                    Msg msg = new Msg(content,Msg.TYPE_SENT);
                    msgList.add(msg);
                    adapter.notifyItemInserted(msgList.size()-1);//有新消息时刷新RecyclerView中的显示
                    msgRecyclerView.scrollToPosition(msgList.size()-1);
                    inputText.setText("");
                }
            }
        });
    }

    private void initMsgs(){
        Msg msg1 = new Msg("Hello guy",Msg.TYPE_RECEIVED);
        msgList.add(msg1);
        Msg msg2 = new Msg("Hello. Who is that",Msg.TYPE_SENT);
        msgList.add(msg2);
        Msg msg3 = new Msg("This is Jerry",Msg.TYPE_RECEIVED);
        msgList.add(msg3);
    }
}

碎片

添加对骗的步骤：
1. 首先创建左右碎片的xml
2. 设置两个类继承Fragment，重写onCreatView，view中引入布局
3. 在主活动布局中引入两个<fragment，name是两个类

动态添加碎片：

创建另一碎片xml
创建另一碎片的类继承Fragment
在主活动布局中创建FrameLayout

在主函数中使用FragmentManager，然后创建FragmentTransaction，替换布局，提交：

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button button = (Button) findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                replaceFragment(new AnotherRightFragment());
            }
        });
        replaceFragment(new RightFragment());
    }

    private void replaceFragment(Fragment fragment){
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction transaction = fragmentManager.beginTransaction();
        transaction.replace(R.id.right_layout,fragment);
        transaction.commit();
    }
}

在碎片中模拟返回栈：

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button button = (Button) findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                replaceFragment(new AnotherRightFragment());
            }
        });
        replaceFragment(new RightFragment());
    }

    private void replaceFragment(Fragment fragment){
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction transaction = fragmentManager.beginTransaction();
        transaction.replace(R.id.right_layout,fragment);
        transaction.addToBackStack(null);//加上这一句就可以了
        transaction.commit();
    }
}

广播机制

分两种：
1. 标准广播：完全异步所有广播接收器都会同步收到
2. 有序广播：同步执行优先级高的广播接收器先收到消息，处理完成后才会继续传递广播或截断

动态注册监听网路变化（在代码中注册广播为动态注册，在AM.xml注册为静态注册，静态注册可以让陈故乡在未启动情况下收到广播）

需要重写BroadcastReceiver来做接收器，接收器类中规定接受广播后的动作；需要一个IntentFilter实例，其中addAction为广播；然后组册广播接收器；还需要重写onDestroy将广播接收器取消注册。

在接收器中，使用getSystemService得到ConnectivityManager实例，然后再通过ConnectivityManager中的getActiveNetworkInfo来得到NetworkInfo实例。

public class MainActivity extends AppCompatActivity {

  private NetworkChangeReceiver networkChangeReceiver;

  private IntentFilter intentFilter;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    intentFilter = new IntentFilter();
    intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");
    networkChangeReceiver = new NetworkChangeReceiver();
    registerReceiver(networkChangeReceiver,intentFilter);
  }

  @Override
  protected void onDestroy() {
    super.onDestroy();
    unregisterReceiver(networkChangeReceiver);
  }

  class NetworkChangeReceiver extends BroadcastReceiver{
    @Override
    public void onReceive(Context context, Intent intent) {
      ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
      NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
      if(networkInfo!=null&&networkInfo.isAvailable()){
        Toast.makeText(context,"network is available",Toast.LENGTH_SHORT).show();
      }else{
        Toast.makeText(context,"network is unavailable",Toast.LENGTH_SHORT).show();
      }
    }
  }
}

注意需要再AM中声明权限：

1	`<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>`

发送自定义广播

发送标准广播：

首先写一个接收器类：

public class MyBroadcastReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context,"received in MyBroadcastReceiver",Toast.LENGTH_SHORT).show();
    }
}

然后在AM中静态注册接收器：

<receiver
          android:name=".MyBroadcastReceiver"
          android:enabled="true"
          android:exported="true">
  <intent-filter>
    <action android:name="com.example.broadcasttest.MY_BROADCAST"/>
  </intent-filter>
</receiver>

在主活动布局添加按钮，然后在主活动中添加点击事件，构建Intent对象，将action放入，然后sendBroadcast：

protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  Button button = (Button) findViewById(R.id.button);
  button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
      Intent intent = new Intent("com.example.broadcasttest.MY_BROADCAST");
      sendBroadcast(intent);
    }
  });

发送有序广播:

发送广播的方法换为sendOrderedBroadcast(intent, null)

protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  Button button = (Button) findViewById(R.id.button);
  button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
      Intent intent = new Intent("com.example.broadcasttest.MY_BROADCAST");
      sendOrderedBroadcast(intent,null);
    }
  });

广播接收器权限从AM中设定 android:priority

<receiver
          android:name=".MyBroadcastReceiver"
          android:enabled="true"
          android:exported="true">
  <intent-filter android:priority="100">
    <action android:name="com.example.broadcasttest.MY_BROADCAST"/>
  </intent-filter>
</receiver>

可以在广播接收器中设置广播截断：

public class MyBroadcastReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context,"received in MyBroadcastReceiver",Toast.LENGTH_SHORT).show();
        abortBroadcast();
    }
}

使用本地广播：

广播只能在应用内部传递，广播接收器只能接受来自应用发出的广播，更高效，只能动态注册；

使用LocalBroadcastManager对本地广播管理

用LocalBroadcastManager.getIntance来获取实例

private IntentFilter intentFilter;
private LocalReceiver localReceiver;
private LocalBroadcastManager localBroadcastManager;

@Override
protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  localBroadcastManager = LocalBroadcastManager.getInstance(this);
  Button button = (Button) findViewById(R.id.button);
  button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
      Intent intent = new Intent("com.example.broadcasttest.LOCAL_BROADCAST");
      localBroadcastManager.sendBroadcast(intent);
    }
  });
  intentFilter = new IntentFilter();
  intentFilter.addAction("com.example.broadcasttest.LOCAL_BROADCAST");
  localReceiver = new LocalReceiver();
  localBroadcastManager.registerReceiver(localReceiver,intentFilter);
}

class LocalReceiver extends BroadcastReceiver {
  @Override
  public void onReceive(Context context, Intent intent) {
    Toast.makeText(context, "received local broadcast", Toast.LENGTH_SHORT).show();
  }
}

持久化存储

有文件存储、SharedPreference存储和数据库存储三种

文件存储

openFileOutput方法，第一个参数为文件名，第二个参数为操作模式（MODE_PRIVATE是覆盖写，MODE_APPEND是追加写）

public class MainActivity extends AppCompatActivity {
    private EditText edit;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        edit = (EditText) findViewById(R.id.edit);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        String inputText = edit.getText().toString();
        save(inputText);
    }

    private void save(String inputText){
        FileOutputStream out = null;
        BufferedWriter writer = null;
        try{
            out = openFileOutput("data",MODE_PRIVATE);//打开一个文件输出
            writer = new BufferedWriter(new OutputStreamWriter(out));//OutputStreamWriter将字节流转为字符流，BufferedOutput用于缓冲写入
            writer.write(inputText);
        }catch (IOException e){
            e.printStackTrace();
        }finally {
            try{
                if(writer != null){
                    writer.close();
                }
            }catch (IOException e){
                e.printStackTrace();
            }
        }
    }
}

读取：

private String load(){
  FileInputStream in = null;
  BufferedReader reader = null;
  StringBuilder content = new StringBuilder();
  try{
    in = openFileInput("data");
    reader = new BufferedReader(new InputStreamReader(in));
    String line = "";
    while((line = reader.readLine())!=null){
      content.append(line);
    }
  }catch (IOException e){
    e.printStackTrace();
  }finally {
    if(reader!=null){
      try{
        reader.close();
      }catch (IOException e){
        e.printStackTrace();
      }
    }
  }
  return content.toString();
}

SharedPreferences存储

键值对

存储到SharedPreferences:

SharedPreferences.Editor editor = getSharedPreferences("data",MODE_PRIVATE).edit();
editor.putString("name","Tom");
editor.putInt("age",28);
editor.putBoolean("married",false);
editor.apply();

调用SharedPreferences对象的edit方法来得到一个SharedPreferences.Editor对象，然后向对象中添加数据，apply方法提交数据。

从SharedPreferences中读取数据

SharedPreferences pref = getSharedPreferences("data",MODE_PRIVATE);
String name = pref.getString("name","");
int age = pref.getInt("age",0);
boolean married = pref.getBoolean("married",false);

用getSharedPreferences得到对象，get读取

SQLite数据存储

创建和升级数据库：

SQLiteOpenHelper是一个抽象类，需要重写onCreate和onUpgrade方法，前者用于数据库创建（构建实例后用getReadableDatabase或getWritableDatabase创建数据库），后者用于数据库版本更新

public class MyDatabaseHelper extends SQLiteOpenHelper {
    public static final String CREATE_BOOK = "create table Book ("+"id integer primary key autoincrement,"+"auther text,"+"price real,"+"pages integer,"+"name text)";

    public static final String CREATE_CATEGORY = "create table Category ("+"id integer primary key autoincrement,"+"category_name text,"+"category_code integer)";
    private Context mContext;

    public MyDatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory,int version){
        super(context,name,factory,version);
        mContext = context;
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_BOOK);
        db.execSQL(CREATE_CATEGORY);
        Toast.makeText(mContext,"Create succeeded",Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("drop table if exists Book");
        db.execSQL("drop table if exists Category");
        onCreate(db);
    }
}

添加数据：

四种操作CRUD：Create Retrieve代表查询 Update代表更新 Delete

可借助getReadableDatabase或getWritableDatabase返回的SQLiteDatabase对象进行CRUD

SQLiteDatabase db = dbHelper.getWritableDatabase();
ContentValues values = new ContentValues();
values.put("author","Dan Brown");
values.put("price",16.96);
values.put("pages",454);
values.put("name","The Da Vinci Code");
db.insert("Book",null,values);

更新数据：

SQLiteDatabase db = dbHelper.getWritableDatabase();
ContentValues values = new ContentValues();
values.put("price",10.99);
db.update("Book",values,"name=?",new String[]{"The Da Vinci Code"});

删除数据：

1 2	`SQLiteDatabase db = dbHelper.getWritableDatabase(); db.delete("Book","pages>?",new String[]{"500"});`

查询数据：最后一定要关闭cursor！

SQLiteDatabase db = dbHelper.getWritableDatabase();
Cursor cursor = db.query("Book",null,null,null,null,null,null);
if(cursor.moveToFirst()){
     do{
        String name = cursor.getString(cursor.getColumnIndex("name"));
        String author = cursor.getString(cursor.getColumnIndex("author"));
        int pages = cursor.getInt(cursor.getColumnIndex("pages"));
        double price = cursor.getDouble(cursor.getColumnIndex("price"));
        Toast.makeText(MainActivity.this,"book name is "+name+"book author is "+author+"book pages is "+pages+"book price is "+price,Toast.LENGTH_SHORT).show();
        }while(cursor.moveToNext());
}
      cursor.close();

使用SQL操作数据库：

添加数据的方法如下：
db.execSQL(“insert into Book (name, author, pages, price) values(?, ?, ?, ?)”,
new String[] { “The Da Vinci Code”, “Dan Brown”, “454”, “16.96” });
db.execSQL(“insert into Book (name, author, pages, price) values(?, ?, ?, ?)”,
new String[] { “The Lost Symbol”, “Dan Brown”, “510”, “19.95” });
更新数据的方法如下：
db.execSQL(“update Book set price = ? where name = ?”, new String[] { “10.99”, “The Da V
删除数据的方法如下：
db.execSQL(“delete from Book where pages > ?”, new String[] { “500” });
查询数据的方法如下：
db.rawQuery(“select * from Book”, null);

使用LitePal操作数据库

https://github.com/guolindev/LitePal?tab=readme-ov-file

内容提供器Content Provider：

安卓运行时权限：程序运行时授予危险权限

用ContextCompat.checkSelfPermission检查权限

用ActivityCompat.requestPermissions授予权限

授予接受后onRequestPermissionsResult类处理结果

public class MainActivity extends AppCompatActivity {

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button makeCall = (Button) findViewById(R.id.make_call);
    makeCall.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
        if(ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.CALL_PHONE) != PackageManager.PERMISSION_GRANTED){
          ActivityCompat.requestPermissions(MainActivity.this,new String[]{Manifest.permission.CALL_PHONE},1);
        }else{
          call();
        }
      }
    });
  }

  private void call(){
    try{
      Intent intent = new Intent(Intent.ACTION_CALL);
      intent.setData(Uri.parse("tel:10086"));
      startActivity(intent);
    }catch (Exception e){
      e.printStackTrace();
    }
  }

  @Override
  public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    switch(requestCode){
      case 1:
        if(grantResults.length>0 && grantResults[0]==PackageManager.PERMISSION_GRANTED){
          call();
        }else {
          Toast.makeText(MainActivity.this,"Permission denied",Toast.LENGTH_SHORT).show();
        }
        break;
      default:
    }
  }

访问其他程序中的数据：

ContentResolver的基本用法：

看书吧

读取系统联系人：

首先在xml布局中添加一个Listview

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/contact_view">
    </ListView>

</LinearLayout>

在MainActivity类中，在onCreate中，首先创建Listview对象，然后构建adapter并放入；ContextCompat.checkSelfPermission检查权限，有权则执行readContacts方法；无权限则用ActivityCompat.requestPermissions申请权限，此后需要重写onRequestPermissionsResult类：授权则执行readContacts方法。

在readContacts方法中，使用getContentResolver().query搭配uri来读取内容提供器提供的内容到cursor中，从cursor中读取信息放入contactsList中，更新adapter，最后关闭cursor。

List<String> contactsList = new ArrayList<>();
ArrayAdapter<String> adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  ListView contactsView = (ListView) findViewById(R.id.contact_view);
  adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1,contactsList);
  contactsView.setAdapter(adapter);
  if(ContextCompat.checkSelfPermission(this, Manifest.permission.READ_CONTACTS)!= PackageManager.PERMISSION_GRANTED){
    ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.READ_CONTACTS},1);
  }else{
    readContacts();
  }
}

private void readContacts(){
  Cursor cursor = null;
  try{
    cursor = getContentResolver().query(ContactsContract.CommonDataKinds.Phone.CONTENT_URI,null,null,null,null);
    if(cursor!=null){
      while(cursor.moveToNext()){
        String displayName = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME));
        String number = cursor.getString(cursor.getColumnIndex(ContactsContract.CommonDataKinds.Phone.NUMBER));
        contactsList.add(displayName+"\n"+number);
      }
      adapter.notifyDataSetChanged();
    }
  }catch (Exception e){
    e.printStackTrace();
  }finally {
    if(cursor!=null){
      cursor.close();
    }
  }
}

@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
  switch(requestCode){
    case 1:
      if(grantResults.length>0&&grantResults[0]==PackageManager.PERMISSION_GRANTED){
        readContacts();
      }else{
        Toast.makeText(this,"You denied the permission", Toast.LENGTH_SHORT).show();
      }
      break;
    default:
  }
}

创建内容提供器

需要继承ContentProvider，重写onCreate、query、insert、update、delete、getType方法。具体看书吧。

实现跨程序数据共享

从DatabaseTest项目上继续开发

创建DatabaseProvider内容提供器，getPathSegments()将”/“后分割

public class DatabaseProvider extends ContentProvider {
  public static final int BOOK_DIR = 0;
  public static final int BOOK_ITEM = 1;
  public static final int CATEGORY_DIR = 2;
  public static final int CATEGORY_ITEM = 3;
  public static final String AUTHORITY = "com.example.databasetest.provider";
  private static UriMatcher uriMatcher;
  private static MyDatabaseHelper dbHelper;

  static{
    uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);//无匹配时返回NO_MATCH
    uriMatcher.addURI(AUTHORITY,"book",BOOK_DIR);
    uriMatcher.addURI(AUTHORITY,"book/#",BOOK_ITEM);
    uriMatcher.addURI(AUTHORITY,"category",CATEGORY_DIR);
    uriMatcher.addURI(AUTHORITY,"category/#",CATEGORY_ITEM);
  }
  public DatabaseProvider() {
  }

  @Override
  public int delete(Uri uri, String selection, String[] selectionArgs) {
    // Implement this to handle requests to delete one or more rows.
    SQLiteDatabase db = dbHelper.getWritableDatabase();
    int deleteRows = 0;
    switch (uriMatcher.match(uri)){
      case BOOK_DIR:
        deleteRows = db.delete("Book",selection,selectionArgs);
        break;
      case BOOK_ITEM:
        String bookId = uri.getPathSegments().get(1);
        deleteRows = db.delete("Book","id=?",new String[]{bookId});
        break;
      case CATEGORY_DIR:
        deleteRows = db.delete("Category",selection,selectionArgs);
        break;
      case CATEGORY_ITEM:
        String categoryId = uri.getPathSegments().get(1);
        deleteRows = db.delete("Category","id=?",new String[]{categoryId});
        break;
      default:
    }
    return deleteRows;
  }

  @Override
  public String getType(Uri uri) {
    // TODO: Implement this to handle requests for the MIME type of the data
    // at the given URI.
    switch (uriMatcher.match(uri)){
      case BOOK_DIR:
        return "vnd.android.cursor.dir/vnd.com.example.databasetest.provider.book";
      case BOOK_ITEM:
        return "vnd.android.cursor.item/vnd.com.example.databasetest.provider.book";
      case CATEGORY_DIR:
        return "vnd.android.cursor.dir/vnd.com.example.databasetest.provider.category";
      case CATEGORY_ITEM:
        return "vnd.android.cursor.item/vnd.com.example.databasetest.provider.category";
    }
    return null;
  }

  @Override
  public Uri insert(Uri uri, ContentValues values) {
    // TODO: Implement this to handle requests to insert a new row.
    SQLiteDatabase db = dbHelper.getWritableDatabase();
    Uri uriReturn = null;
    switch(uriMatcher.match(uri)){
      case BOOK_DIR:
      case BOOK_ITEM:
        long newBookId = db.insert("Book",null,values);
        uriReturn = Uri.parse("content://"+AUTHORITY+"/book/"+newBookId);
        break;
      case CATEGORY_DIR:
      case CATEGORY_ITEM:
        long newCategoryId = db.insert("Category",null,values);
        uriReturn = Uri.parse("content://"+AUTHORITY+"/category/"+newCategoryId);
        break;
      default:
        break;
    }
    return uriReturn;
  }

  @Override
  public boolean onCreate() {
    // TODO: Implement this to initialize your content provider on startup.
    dbHelper = new MyDatabaseHelper(getContext(),"BookStore.db",null,2);
    return true;
  }

  @Override
  public Cursor query(Uri uri, String[] projection, String selection,
                      String[] selectionArgs, String sortOrder) {
    // TODO: Implement this to handle query requests from clients.
    SQLiteDatabase db = dbHelper.getReadableDatabase();
    Cursor cursor = null;
    switch(uriMatcher.match(uri)){
      case BOOK_DIR:
        cursor = db.query("Book",projection,selection,selectionArgs,null,null,sortOrder);
        break;
      case BOOK_ITEM:
        String bookId = uri.getPathSegments().get(1);
        cursor = db.query("Book",projection,"id=?",new String[]{bookId},null,null,sortOrder);
        break;
      case CATEGORY_DIR:
        cursor = db.query("Category",projection,selection,selectionArgs,null,null,sortOrder);
        break;
      case CATEGORY_ITEM:
        String categoryId = uri.getPathSegments().get(1);
        cursor = db.query("Category",projection,"id=?",new String[]{categoryId},null,null,sortOrder);
        break;
      default:
        break;
    }
    return cursor;
  }

  @Override
  public int update(Uri uri, ContentValues values, String selection,
                    String[] selectionArgs) {
    // TODO: Implement this to handle requests to update one or more rows.
    SQLiteDatabase db = dbHelper.getWritableDatabase();
    int updateRows = 0;
    switch(uriMatcher.match(uri)){
      case BOOK_DIR:
        updateRows = db.update("Book",values,selection,selectionArgs);
        break;
      case BOOK_ITEM:
        String bookId = uri.getPathSegments().get(1);
        updateRows = db.update("Book",values,"id=?",new String[]{bookId});
        break;
      case CATEGORY_DIR:
        updateRows = db.update("Category",values,selection,selectionArgs);
        break;
      case CATEGORY_ITEM:
        String categoryId = uri.getPathSegments().get(1);
        updateRows = db.update("Category",values,"id=?",new String[]{categoryId});
        break;
      default:
    }
    return updateRows;
  }
}

在AM中注册：自动

运用多媒体

使用通知

NotificationManager manager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
Notification notification = new NotificationCompat.Builder(MainActivity.this)
                        .setContentTitle("This is content title")
                        .setContentText("This is content text")
                        .setWhen(System.currentTimeMillis())
                        .setSmallIcon(R.mipmap.ic_launcher)    .setLargeIcon(BitmapFactory.decodeResource(getResources(),R.mipmap.ic_launcher)).build();
manager.notify(1,notification);

设置意图PendingIntent来启动Intent，设置自动取消：

Intent intent = new Intent(MainActivity.this,NotificationActivity.class);
                PendingIntent pi = PendingIntent.getActivity(MainActivity.this,0,intent,0);
                NotificationManager manager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
                Notification notification = new NotificationCompat.Builder(MainActivity.this)
                        .setContentTitle("This is content title")
                        .setContentText("This is content text")
                        .setWhen(System.currentTimeMillis())
                        .setSmallIcon(R.mipmap.ic_launcher)
                        .setLargeIcon(BitmapFactory.decodeResource(getResources(),R.mipmap.ic_launcher))
                        .setContentIntent(pi)
                        .setAutoCancel(true)
                        .build();
                manager.notify(1,notification);

调用摄像头

在主活动xml中添加按钮和ImageView，用来拍照和显示照片

在MainActivity中给按钮添加点击动作：创建File对象，参数为getCacheDir返回内部缓存路径和文件名；如果文件存在则删除，创建文件；接下来需要把文件对象转为uri，在a7.0以下只需要Uri.fromFile放入File文件即可，在a7.0及以上需要调用FileProvider（这是内容提供器，需在AM注册）的getUriForFile方法，三个参数为环境、唯一字符串和File对象；最后构建Intent对象，action为android.media.action.IMAGE_CAPTURE，再调用Intent的putExtra，第一个参数为MediaStore.EXTRA_OUTPUT用于指定相机应用将拍摄的照片保存到的 URI 地址，第二个参数放入前面得到的uri，然后用startActivityForResult启动intent（需要重写onActivityResult）。

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button takeButton = (Button) findViewById(R.id.take_photo);
        picture = (ImageView) findViewById(R.id.picture);
        takeButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                File outputImage = new File(getCacheDir(),"output_image.jpg");
                try{
                    if(outputImage.exists()){
                        outputImage.delete();
                    }
                    outputImage.createNewFile();
                }catch (IOException e){
                    e.printStackTrace();
                }
                if(Build.VERSION.SDK_INT>=24){
                    imageUri = FileProvider.getUriForFile(MainActivity.this,"com.example.cameraalbumtest.fileprovider",outputImage);
                }else{
                    imageUri = Uri.fromFile(outputImage);
                }
                Intent intent = new Intent("android.media.action.IMAGE_CAPTURE");
                intent.putExtra(MediaStore.EXTRA_OUTPUT,imageUri);
                startActivityForResult(intent,1);
            }
        });
    }

重写onActivityResult：

如果拍照成功，则调用BitmapFactory的decodeStream方法将照片解析为Bitmap对象，用getContentResolver().openInputStream把uri引入；然后ImageView对象setImageBitmap

@Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
    switch (requestCode){
        case 1:
            if(resultCode == RESULT_OK){
                try{
                    Bitmap bitmap = BitmapFactory.decodeStream(getContentResolver().openInputStream(imageUri));
                    picture.setImageBitmap(bitmap);
                }catch (FileNotFoundException e){
                    e.printStackTrace();
                }
          
            }
            break;
        default:
    }
}

在AM注册Provider

<provider
    android:name="androidx.core.content.FileProvider"
    android:authorities="com.example.cameraalbumtest.fileprovider"
    android:exported="false"
    android:grantUriPermissions="true">
    <meta-data
        android:name="android.support.FILE_PROVIDER_PATHS"
        android:resource="@xml/file_paths"/>
</provider>

android:authorities属性的值必须要和刚才FileProvider.getUriForFile()方法中的第二个参数一致；在<provider>标签的内部使用<meta-data>来指定Uri的共享路径，并引用了一个@xml/file_paths资源

创建file_paths.xml文件，name属性的值可以随便填，path属性的值表示共享的具体路径（. 表示当前目录，也就是应用程序的缓存目录的根目录。这意味着 FileProvider 可以共享应用程序缓存目录中的所有文件。）

<?xml version="1.0" encoding="utf-8" ?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <cache-path name="my_images" path="."/>
</paths>

从相册选择照片：第二版书中内容太旧，在a14已无法使用

播放多媒体文件：

播放音频MediaPlayer

private MediaPlayer mediaPlayer = new MediaPlayer();
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button play = (Button) findViewById(R.id.play);
    Button pause = (Button) findViewById(R.id.pause);
    Button stop = (Button) findViewById(R.id.stop);
    play.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if(!mediaPlayer.isPlaying()){
                mediaPlayer.start();
            }
        }
    });
    pause.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if(mediaPlayer.isPlaying()){
                mediaPlayer.pause();
            }
        }
    });
    stop.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if(mediaPlayer.isPlaying()){
                mediaPlayer.stop();
                initMediaPlayer();
            }
        }
    });
    if(ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.WRITE_EXTERNAL_STORAGE)!= PackageManager.PERMISSION_GRANTED){
        ActivityCompat.requestPermissions(MainActivity.this,new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},1);
    }else{
        initMediaPlayer();
    }
}
          
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    switch (requestCode){
        case 1:
            if(grantResults.length>0&&grantResults[0]==PackageManager.PERMISSION_GRANTED){
                initMediaPlayer();
            }else{
                Toast.makeText(this,"拒绝权限将无法使用程序", Toast.LENGTH_SHORT).show();
                finish();
            }
            break;
        default:
    }
}
          
private void initMediaPlayer(){
    try{
        File file = new File(Environment.getExternalStorageDirectory(),"music.mp3");
        mediaPlayer.setDataSource(file.getPath());
        mediaPlayer.prepare();
    }catch (Exception e){
        e.printStackTrace();
    }
}
          
@Override
protected void onDestroy() {
    super.onDestroy();
    if(mediaPlayer!=null){
        mediaPlayer.stop();
    mediaPlayer.release();}
}

播放视频VideoView：看书吧

使用网络技术

WebView用法

使用WebView显示网页：

WebView webView = findViewById(R.id.web_view);
webView.getSettings().setJavaScriptEnabled(true);
webView.setWebViewClient(new WebViewClient());//仍在此WebView中显示而不是跳转浏览器
webView.loadUrl("https://music.apple.com/");

使用http协议访问网络

使用HttpURLConnection

TextView responseText;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    EdgeToEdge.enable(this);
    setContentView(R.layout.activity_main);
    ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {
        Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
        v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom);
        return insets;
    });
    Button sendRequest = findViewById(R.id.send_request);
    sendRequest.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            sendRequestWithHttpURLConnection();
        }
    });
    responseText = findViewById(R.id.response_test);
}
          
private void sendRequestWithHttpURLConnection() {
    new Thread(new Runnable() {
        @Override
        public void run() {
            HttpURLConnection connection = null;
            BufferedReader reader = null;
            try{
                URL url = new URL("https://www.baidu.com");
                connection = (HttpURLConnection) url.openConnection();
                connection.setRequestMethod("GET");
                connection.setConnectTimeout(8000);
                connection.setReadTimeout(8000);
                InputStream in = connection.getInputStream();
                //下面对获取到的输入流进行读取
                reader = new BufferedReader(new InputStreamReader(in));
                StringBuilder response = new StringBuilder();
                String line;
                while((line = reader.readLine())!=null){
                    response.append(line);
                }
                showResponse(response.toString());
            } catch (Exception e) {
                throw new RuntimeException(e);
            }finally {
                if(reader!=null){
                    try{
                        reader.close();
                    }catch (IOException e){
                        e.printStackTrace();
                    }
                }
                if(connection!=null){
                    connection.disconnect();
                }
            }
        }
    }).start();
}
private void showResponse(String response){
    runOnUiThread(new Runnable() {
        @Override
        public void run() {
            responseText.setText(response);
        }
    });
}

使用OkHttp：

private void sendRequestWithOkHttp(){
    new Thread(new Runnable() {
        @Override
        public void run() {
            try {
                OkHttpClient client = new OkHttpClient();
                Request request = new Request.Builder()
                        .url("https://www.baidu.com")
                        .build();
                Response response = client.newCall(request).execute();
                String responseData = response.body().string();
                showResponse(responseData);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }).start();
}

解析xml格式数据

有点难看书吧

服务

多线程编程：
1. 在子线程中更新UI
  
  经过测试这是不被允许的
  
  android提供了一套异步消息处理机制，解决子线程中进行ui操作的问题
2. 异步消息处理机制：
  
  主要由4个部分组成：Message Handler MessageQuene Looper
  
  Message
  
  Message是在线程之间传递的消息，它可以在内部携带少量的信息，用于在不同线程之间交换数据。上一小节中我们使用到了Message的what字段，除此之外还可以使用arg1和arg2字段来携带一些整型数据，使用obj字段携带一个Object对象。
  
  Handler
  
  Handler顾名思义也就是处理者的意思，它主要是用于发送和处理消息的。发送消息一般是使用Handler的sendMessage()方法，而发出的消息经过一系列地辗转处理后，最终会传递到Handler的handleMessage()方法中。
  
  MessageQueue
  
  MessageQueue是消息队列的意思，它主要用于存放所有通过Handler发送的消息。这部分消息会一直存在于消息队列中，等待被处理。每个线程中只会有一个MessageQueue对象。
  
  Looper
  
  Looper是每个线程中的MessageQueue的管家，调用Looper的loop()方法后，就会进入到一个无限循环当中，然后每当发现MessageQueue中存在一条消息，就会将它取出，并传递到Handler的handleMessage()方法中。每个线程中也只会有一个Looper对象。
  
  异步消息处理的整个流程：
  
  首先，需要在主线程当中创建一个Handler对象，并重写handleMessage()方法。
  然后，当子线程中需要进行UI操作时，就创建一个Message对象，并通过Handler将这条消息发送出去。之后，这条消息会被添加到MessageQueue的队列中等待被处理，而Looper则会一直尝试从MessageQueue中取出待处理消息。
3. 使用AsyncTask：
  
  这是一个抽象类，继承需要重写onPreExecute doInBackground onProgressUpdate onPostExecute，需要设置三个泛型参数Params Progress Result

服务

定义一个服务

可以重写

onCreate() 方法会在服务创建的时候调用。
onStartCommand() 方法会在每次服务启动的时候调用。
onDestroy() 方法会在服务销毁的时候调用。

startService.setOnClickListener(new View.OnClickListener() {
  @Override
  public void onClick(View v) {
    Intent startIntent = new Intent(MainActivity.this, MyService.class);
    startService(startIntent);
  }
});
stopService.setOnClickListener(new View.OnClickListener() {
  @Override
  public void onClick(View v) {
    Intent stopIntent = new Intent(MainActivity.this, MyService.class);
    stopService(stopIntent);
  }
});

活动和服务进行通信

首先在服务的代码中继承Binder，写一些方法；创建一个实例；然后在onBind中返回实例。

public class MyService extends Service {
    public MyService() {
    }

    class DownloadBinder extends Binder{
        public void startDownload(){
            Log.d("MyService","startDownload executed");
        }
        public int getProgress(){
            Log.d("MyService","getProgress executed");
            return 0;
        }
    }
    private DownloadBinder mBinder = new DownloadBinder();
 ...

然后在活动代码中创建ServiceConnection的匿名类，然后重写两个方法；在绑定服务和活动时使用bindService三个参数：bindIntent对象，ServiceConnection实例，和标志位（这里传入BIND_AUTO_CREATE表示在活动和服务进行绑定后自动创建服务。这会使得MyService中的onCreate()方法得到执行，但onStartCommand()方法不会执行。）

private MyService.DownloadBinder downloadBinder;
private ServiceConnection connection = new ServiceConnection() {
  @Override
  public void onServiceConnected(ComponentName name, IBinder service) {
    downloadBinder = (MyService.DownloadBinder) service;
    downloadBinder.startDownload();
    downloadBinder.getProgress();
  }

  @Override
  public void onServiceDisconnected(ComponentName name) {
  }
};

@Override
protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  ...
    Button bindService = findViewById(R.id.bind_service);
  Button unbindService = findViewById(R.id.unbind_service);
  bindService.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
      Intent bindIntent = new Intent(MainActivity.this, MyService.class);
      bindService(bindIntent,connection,BIND_AUTO_CREATE);
    }
  });
  unbindService.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
      unbindService(connection);
    }
  }

服务的生命周期：

服务也有自己的生命周期，前面我们使用到的onCreate()、onStartCommand()、onBind()和onDestroy()等方法都是在服务的生命周期内可能回调的方法。

一旦在项目的任何位置调用了Context的startService()方法，相应的服务就会启动起来，并回调onStartCommand()方法。如果这个服务之前还没有创建过，onCreate()方法会先于onStartCommand()方法执行。服务启动了之后会一直保持运行状态，直到stopService()或stopSelf()方法被调用。

注意，虽然每调用一次startService()方法，onStartCommand()就会执行一次，但实际上每个服务都只会存在一个实例。所以不管你调用了多少次startService()方法，只需调用一次stopService()或stopSelf()方法，服务就会停止下来了。

另外，还可以调用Context的bindService()来获取一个服务的持久连接，这时就会回调服务中的onBind()方法。类似地，如果这个服务之前还没有创建过，onCreate()方法会先于onBind()方法执行。之后，调用方可以获取到onBind()方法里返回的IBinder对象的实例，这样就能自由地和服务进行通信了。只要调用方和服务之间的连接没有断开，服务就会一直保持运行状态。

当调用了startService()方法后，又去调用stopService()方法，这时服务中的onDestroy()方法就会执行，表示服务已经销毁了。类似地，当调用了bindService()方法后，又去调用unbindService()方法，onDestroy()方法也会执行。

需要注意，我们是完全有可能对一个服务既调用了startService()方法，又调用了bindService()方法的，这种情况下该如何才能让服务销毁掉呢？根据Android系统的机制，一个服务只要被启动或者被绑定了之后，就会一直处于运行状态，必须要让以上两种条件同时不满足，服务才能被销毁。所以，这种情况下要同时调用stopService()和unbindService()方法，onDestroy()方法才会执行。

服务的更多技巧：

使用前台服务：

前台服务优先级高，免杀。

public void onCreate() {
  super.onCreate();
  Log.d("MyService", "onCreate executed");

  // 创建通知渠道（仅在 Android 8.0 及更高版本需要）
  if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
    NotificationChannel channel = new NotificationChannel("my_channel_id", "My Channel Name", NotificationManager.IMPORTANCE_DEFAULT);
    NotificationManager manager = getSystemService(NotificationManager.class);
    manager.createNotificationChannel(channel);
  }

  Intent intent = new Intent(this, MainActivity.class);
  PendingIntent pi = PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_IMMUTABLE);
  Notification notification = new NotificationCompat.Builder(this, "my_channel_id")
    .setContentText("This is content text")
    .setContentTitle("This is content title")
    .setWhen(System.currentTimeMillis())
    .setSmallIcon(R.mipmap.ic_launcher)
    .setLargeIcon(BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher))
    .setContentIntent(pi)
    .build();
  startForeground(1, notification);
}

使用IntentService

用它建立线程执行完成后会自动destory

当您使用 startService() 方法启动 IntentService 时，IntentService 会创建一个工作线程。
IntentService 会将收到的 Intent 放入一个工作队列中。
工作线程会依次从工作队列中取出 Intent，并调用 onHandleIntent() 方法来处理 Intent。
onHandleIntent() 方法执行完毕后，工作线程会自动停止。
如果工作队列中还有其他 Intent，工作线程会继续处理，直到所有 Intent 都处理完毕。因此，onHandleIntent() 方法会在以下情况下被调用：

先继承IntentService来写服务内容

public class MyIntentService extends IntentService {
    public MyIntentService() {
        super("MyIntentService");
    }

    @Override
    protected void onHandleIntent(@Nullable Intent intent) {
        Log.d("MyIntentService", "Thread id is"+Thread.currentThread().getId());
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.d("MyIntentService","onDestory executed");
    }
}

然后在活动中创建使用startService方法；

最后不要忘记在AM中注册service。

服务的最佳实践下载示例

首先定义一个回到接口，用于对下载过程中的各种状态进行监听和回调

public interface DownloadListner {
    void onProgress(int progress);
    void onSuccess();
    void onFailed();
    void onPaused();
    void onCanceled();
}

写DownloadTask类继承AsyncTask，实现子线程工作

public class DownloadTask extends AsyncTask<String,Integer,Integer> {
    public static final int TYPE_SUCCESS = 0;
    public static final int TYPE_FAILED = 1;
    public static final int TYPE_PAUSED = 2;
    public static final int TYPE_CANCELED = 3;

    private DownloadListner listener;
    private boolean isCanceled = false;
    private boolean isPaused = false;
    private int lastProgress;

    public DownloadTask(DownloadListner listener) {
        this.listener = listener;
    }

    @Override
    protected Integer doInBackground(String... strings) {
        InputStream is = null;
        RandomAccessFile savedFile = null;
        File file = null;
        try{
            long downloadedLength = 0;
            String downloadUrl = strings[0];
            String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));
            String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();
            file = new File(directory+fileName);
            if(file.exists()){
                downloadedLength = file.length();
            }
            long contentLength = getContentLength(downloadUrl);
            if(contentLength==0){
                return TYPE_FAILED;
            }else if(contentLength==downloadedLength){
                return TYPE_SUCCESS;
            }
            OkHttpClient client = new OkHttpClient();
            Request request = new Request.Builder()
                    .addHeader("RANGE","bytes="+downloadedLength+"-")
                    .url(downloadUrl)
                    .build();
            Response response = client.newCall(request).execute();
            if(response != null){
                is = response.body().byteStream();
                savedFile = new RandomAccessFile(file,"rw");
                savedFile.seek(downloadedLength);
                byte[] b = new byte[1024];
                int total = 0;
                int len;
                while((len=is.read(b))!=-1){
                    if(isCanceled){
                        return TYPE_CANCELED;
                    }else if(isPaused){
                        return TYPE_PAUSED;
                    }else{
                        total += len;
                        savedFile.write(b,0,len);
                        int progress = (int) ((total+downloadedLength)*100/contentLength);
                        publishProgress(progress);
                    }
                }
                response.body().close();
                return TYPE_SUCCESS;
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            try{
                if(is != null){
                    is.close();
                }
                if(savedFile != null){
                    savedFile.close();
                }
                if(isCanceled&&file != null){
                    file.delete();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return TYPE_FAILED;
    }

    @Override
    protected void onProgressUpdate(Integer... values) {
        int progress = values[0];
        if(progress>lastProgress){
            listener.onProgress(progress);
            lastProgress = progress;
        }
    }

    @Override
    protected void onPostExecute(Integer integer) {
        switch(integer){
            case TYPE_SUCCESS:
                listener.onSuccess();
                break;
            case TYPE_FAILED:
                listener.onFailed();
                break;
            case TYPE_PAUSED:
                listener.onPaused();
                break;
            case TYPE_CANCELED:
                listener.onCanceled();
                break;
            default:
        }
    }
    public void pauseDownload(){
        isPaused = true;
    }
    public void cancelDownload(){
        isCanceled = true;
    }
    private long getContentLength(String downloadUrl) throws IOException{
        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder()
                .url(downloadUrl)
                .build();
        Response response = client.newCall(request).execute();
        if(response!= null&&response.isSuccessful()){
            long contentLength = response.body().contentLength();
            response.body().close();
            return contentLength;
        }
        return 0;
    }
}

写DownloadService服务类，在里面重写并实例了DownloadListener接口，并写DownloadBinder继承Binder，在binder的任务开始方法中将DownloadTask实例并放入参数为DownloadListener实例

public class DownloadService extends Service {
    private DownloadTask downloadTask;
    private String downloadUrl;

    private DownloadListner listner = new DownloadListner() {
        @Override
        public void onProgress(int progress) {
            getNotificationManager().notify(1,getNotification("Downloading...",progress));
        }

        @Override
        public void onSuccess() {
            downloadTask = null;
            stopForeground(true);
            getNotificationManager().notify(1,getNotification("Download Success",-1));
            Toast.makeText(DownloadService.this,"Download success",Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onFailed() {
            downloadTask = null;
            stopForeground(true);
            getNotificationManager().notify(1,getNotification("Download Failed",-1));
            Toast.makeText(DownloadService.this,"Download failed",Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onPaused() {
            downloadTask = null;
            Toast.makeText(DownloadService.this,"Paused",Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onCanceled() {
            downloadTask = null;
            stopForeground(true);
            Toast.makeText(DownloadService.this,"Canceled",Toast.LENGTH_SHORT).show();
        }
    };
    public DownloadService() {
    }

    private DownloadBinder mBinder = new DownloadBinder();
    @Override
    public IBinder onBind(Intent intent) {
        // TODO: Return the communication channel to the service.
        return mBinder;
    }
    class DownloadBinder extends Binder {
        @SuppressLint("ForegroundServiceType")
        public void startDownload(String url){
            if(downloadTask==null){
                downloadUrl = url;
                downloadTask = new DownloadTask(listner);
                downloadTask.execute(downloadUrl);
                startForeground(1,getNotification("Downloding...",0));
                Toast.makeText(DownloadService.this,"Downloading...",Toast.LENGTH_SHORT).show();
            }
        }
        public void pauseDownload(){
            if(downloadTask!=null){
                downloadTask.pauseDownload();
            }
        }
        public void cancelDownload(){
            if (downloadTask != null) {
                downloadTask.cancelDownload();
            }else{
                if(downloadUrl!=null){
                    String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/"));
                    String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath();
                    File file = new File(directory+fileName);
                    if(file.exists()){
                        file.delete();
                    }
                    getNotificationManager().cancel(1);
                    stopForeground(true);
                    Toast.makeText(DownloadService.this,"Canceled",Toast.LENGTH_SHORT).show();
                }
            }
        }
    }
    private NotificationManager getNotificationManager(){
        return (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
    }
    private Notification getNotification(String title,int progress){
        Intent intent = new Intent(this,MainActivity.class);
        PendingIntent pi = PendingIntent.getActivity(this,0,intent,PendingIntent.FLAG_IMMUTABLE);
        NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
        builder.setSmallIcon(R.mipmap.ic_launcher);
        builder.setLargeIcon(BitmapFactory.decodeResource(getResources(),R.mipmap.ic_launcher));
        builder.setContentIntent(pi);
        builder.setContentTitle(title);
        if(progress>=0){
            builder.setContentText(progress+"%");
            builder.setProgress(100,progress,false);
        }
        return builder.build();
    }
}

在活动中创建DownloadBinder实例，并创建服务连接，定义连接中的活动，为按键定义活动。需要请求写存储权限，需要网络权限，需要在活动结束后解除binder绑定：

public class MainActivity extends AppCompatActivity {
    private DownloadService.DownloadBinder downloadBinder;
    private ServiceConnection connection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            downloadBinder = (DownloadService.DownloadBinder) service;
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {

        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        EdgeToEdge.enable(this);
        setContentView(R.layout.activity_main);
        ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {
            Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
            v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom);
            return insets;
        });

        Button startDownload = findViewById(R.id.start_download);
        Button pauseDownload = findViewById(R.id.pause_download);
        Button cancelDownload = findViewById(R.id.cancel_download);
        startDownload.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String url = "https://github.com/BIGGGJerry/Course_In_SDUCST/archive/refs/heads/main.zip";
                downloadBinder.startDownload(url);
            }
        });
        pauseDownload.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                downloadBinder.pauseDownload();
            }
        });
        cancelDownload.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                downloadBinder.cancelDownload();
            }
        });
        Intent intent = new Intent(this,DownloadService.class);
        startService(intent);
        bindService(intent,connection,BIND_AUTO_CREATE);
        if(ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.WRITE_EXTERNAL_STORAGE)!= PackageManager.PERMISSION_GRANTED){
            ActivityCompat.requestPermissions(MainActivity.this,new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},1);
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        switch (requestCode){
            case 1:
                if(grantResults.length>0&&grantResults[0]!=PackageManager.PERMISSION_GRANTED){
                    Toast.makeText(this,"拒绝权限将无法使用程序",Toast.LENGTH_SHORT).show();
                    finish();
                }
                break;
            default:
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        unbindService(connection);
    }
}

知识

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