（八）Android广播接收器BroadcastReceiver

一、使用Broadcast Reciver

1.右击java文件夹，new->other->Broadcast Receiver后会在AndroidManifest.xml文件中生成一个receiver项

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.shiyanshi.learnbroadcast" >

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>

</manifest>

2.同时生成了一个MyReceiver 的类，该类中onReceive用于响应sendBroadcast函数发送的消息

package com.example.shiyanshi.learnbroadcast;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;

public class MyReceiver extends BroadcastReceiver {
    public MyReceiver() {
    }

    @Override

public void onReceive(Context context, Intent intent) {
// TODO: This method is called when the BroadcastReceiver is receiving
// an Intent broadcast.
// throw new UnsupportedOperationException("Not yet implemented");
System.out.println("Recv Data:"+intent.getStringExtra("data"));
}

3.调用sendBroadcast函数进行发送消息，该函数需要一个Intent

package com.example.shiyanshi.learnbroadcast;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;

public class MainActivity extends Activity implements View.OnClickListener {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        findViewById(R.id.btnSendMsg).setOnClickListener(this);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.btnSendMsg:

Intent intent =new Intent(this,MyReceiver.class);
intent.putExtra("data","henry");
sendBroadcast(intent);

                break;
        }
    }
}

二、动态注册和注销

1.删去AndroidManifest.xml文件中的receiver时，需要动态注册和注销，才能发送和接收消息

<receiver
android:name=".MyReceiver"

android:enabled="true"

android:exported="true" >

</receiver>

2.MainActivity更改如下：发送消息消息时，Intent要使用隐式Intent（MyReceiver.ACTION为定义的一个常量字符串

public static final String ACTION="com.example.shiyanshi.learnbroadcast.intent.action.MyReceiver";//前半部分时包名，后半部分时intent的格式，MyReceiver是上述中用于

响应sendBroadcast的类），注册时使用registerReceiver函数，注销时使用unregisterReceiver函数

函数原型为：

public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter)

public void unregisterReceiver(BroadcastReceiver receiver)

receiver是我们新建Broadcast时声称的用于响应sendBroadcast的MyReceiver类，filter是过滤器，需想起传递隐式Intent类似的参数。

public class MainActivity extends Activity implements View.OnClickListener {

private MyReceiver receiver=null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        findViewById(R.id.btnSendMsg).setOnClickListener(this);
        findViewById(R.id.btnRegister).setOnClickListener(this);
        findViewById(R.id.btnUnregister).setOnClickListener(this);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.btnSendMsg:
//                Intent intent =new Intent(this,MyReceiver.class);

//动态注册和注销时要使用隐式Intent，而不能使用显示Intent了
Intent intent=new Intent(MyReceiver.ACTION);

                intent.putExtra("data","henry");
                sendBroadcast(intent);
                break;

case R.id.btnRegister:
if (receiver==null){
receiver=new MyReceiver();
registerReceiver(receiver,new IntentFilter(MyReceiver.ACTION));
}
break;
case R.id.btnUnregister:
if(receiver!=null){
unregisterReceiver(receiver);
receiver=null;
}
break;

        }
    }
}

三、Broadcast的优先级

当发送数据时，采用隐式Intent的形式（如上），两个receiver中的action name相同时，二者可以同时接收到数据。

默认情况下最后写的那个receiver所对应的优先级高，此外可以显示的在receiver下的Intent-filter中指明优先级priority，其数值越大，优先级越高，越先响应数据

 <receiver
        android:name=".MyReceiver1"
        android:enabled="true"
        android:exported="true" >
        <intent-filter android:priority="2">
            <action android:name="com.example.shiyanshi.learnbroadcast.intent.action.MyReceiver"/>
        </intent-filter>
    </receiver>
    <receiver android:name=".MyReceiver"
        android:enabled="true"
        android:exported="true">
        <intent-filter android:priority="1">
            <action android:name="com.example.shiyanshi.learnbroadcast.intent.action.MyReceiver"/>
        </intent-filter>
    </receiver>
</application>

此外，当优先级高的那个onReceive执行后，可以在其中调用abortBroadcast来终止数据的传递，优先级别低的onReceive便不会执行了.

注意：若想使用abortBroadcast函数，发送时需使用sendOrderedBroadcast而非sendBroadcast，否则会弹出错误java.lang.RuntimeException: BroadcastReceiver trying to return result during a non-ordered broadcast。

Intent intent=new Intent(MyReceiver.ACTION);
                intent.putExtra("data","henry");
//                sendBroadcast(intent);
                sendOrderedBroadcast(intent,null);

其中sendOrderedBroadcast的第二个参数用来指明权限，可以为空