Android_四大组件之BroadcastReceiver

一、概述

BroadcastReceiver是广播接收器，接收来自 系统或应用发出的广播信息 并进行相应的逻辑处理。

自定义BroadcastReceiver只需继承android.content.BroadcastReceiver，并重写onReceive()方法就可以了。

public class StaticBroadcastReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        //TODO
    }
}

二、基本用法

1.BroadcastReceiver注册：

BroadcastReceiver有两种注册方法，静态注册和动态注册，下面分别说明。

（1）静态注册

在AndroidManifest.xml中通过<receiver>标签 注册的广播，即是静态注册。 静态注册后的广播，在系统启动后，就一直常驻系统内存中，接收符合的广播信息，不管应用是否处于运行状态。

所以它的优点是常驻系统，时刻运行，不受应用及其他组件生命周期的影响；缺点是常驻内存 耗电。比较适合实时监听的场景。

/*
android:exported与其他组件的属性意义相同，如果这里为false,则不接受其他组件的广播，只接收本地应用的广播
*/

<receiver android:name=".StaticBroadcastReceiver"
            android:enabled="true"
            android:exported="true">
    <intent-filter>
        <action android:name="com.flx.testBroadcastReceiver.TEST_BROADCAST_RECEIVER"></action>
    </intent-filter>
</receiver>

注册静态广播的广播接收类。

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

public class StaticBroadcastReceiver extends BroadcastReceiver {
    final private static String TAG = "StaticBroadcastReceiver";
    @Override
    public void onReceive(Context context, Intent intent) {
        Log.d(TAG, "onReceive: "+intent.getStringExtra("testkey"));
    }
}

发送广播：

Button sendBroadcastBtn = findViewById(R.id.send_broadcast_btn);
sendBroadcastBtn.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Log.d("StaticBroadcastReceiver", "click");
        Intent broadcastIntent = new Intent();
        broadcastIntent.setAction("com.flx.testBroadcastReceiver.TEST_BROADCAST_RECEIVER");
        broadcastIntent.putExtra("testkey", "testval");
        sendBroadcast(broadcastIntent);
    }
});

但是 通过log 发现接收器StaticBroadcastReceiver 并没有接收到广播，这是怎么回事呢？看log，报错如下：

2019-07-31 03:17:50.978 883-922/system_process W/BroadcastQueue: Background execution not allowed: receiving Intent 
{ act=com.flx.testBroadcastReceiver.TEST_BROADCAST_RECEIVER flg=0x10 (has extras) } to com.flx.testBroadcastReceiver/.StaticBroadcastReceiver

因为是在P上调试的，O以后系统对隐式广播(没有指明接收广播的组件的)做了限制，所以无法接收。 网上有一些关于如何绕过这一限制 可以让静态注册接收到隐式广播的，但没发现特别好的，若非必要 也不需要这样做。自定义的广播一般知道目标接收器的组件等信息的，而且动态注册(后面讲的)不受这一限制。

官网上说明：
Android 8.0
Beginning with Android 8.0 (API level 26), the system imposes additional restrictions on manifest-declared receivers.

If your app targets Android 8.0 or higher, you cannot use the manifest to declare a receiver for most implicit broadcasts 
(broadcasts that don't target your app specifically). You can still use a context-registered receiver when the user is actively using your app.

这里就不发送隐式广播就可以接收了。

        Button sendBroadcastBtn = findViewById(R.id.send_broadcast_btn);
        sendBroadcastBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d("StaticBroadcastReceiver", "click");
                Intent broadcastIntent = new Intent();
                broadcastIntent.setAction("com.flx.testBroadcastReceiver.TEST_BROADCAST_RECEIVER");
                broadcastIntent.putExtra("testkey", "testval");
            broadcastIntent.setPackage("com.flx.testBroadcastReceiver");
                sendBroadcast(broadcastIntent);
            }
        });

2019-07-31 03:46:24.810 21336-21336/com.flx.testBroadcastReceiver D/StaticBroadcastReceiver: click
2019-07-31 03:46:24.857 21336-21336/com.flx.testBroadcastReceiver D/StaticBroadcastReceiver: onReceive: testval

(2)动态注册

动态注册，需要在代码中通过registerReceiver(BroadcastReceiver receiver, IntentFilter filter)进行注册 的。只有当广播接收者通过registerReceiver()注册后，才能接收广播进行处理。

动态注册不受隐式广播的限制。

动态注册的广播通过unregisterReceiver(BroadcastReceiver receiver)去销毁，否则会报错。

动态注册非常驻系统，受组件生命周期影响，适用于在特定时刻监听广播的场景。

动态广播接收器

public class DanymicBroadcastReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Log.d("flx_broadcast", "DanymicBroadcastReceiver onReceive: " + intent.getStringExtra("testkey"));
    }
}

动态注册和销毁

import android.app.Activity;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity {
    final private String TEST_ACTION = "com.flx.testBroadcastReceiver.TEST_BROADCAST_RECEIVER";
    private DanymicBroadcastReceiver mDanymicBroadcastReceiver =  new DanymicBroadcastReceiver();

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

        Button sendBroadcastBtn = findViewById(R.id.send_broadcast_btn);
        sendBroadcastBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d("flx_broadcast", "click");
                Intent broadcastIntent = new Intent();
                broadcastIntent.setAction(TEST_ACTION);
                broadcastIntent.putExtra("testkey", "testval");
//                broadcastIntent.setPackage("com.flx.testBroadcastReceiver");
                sendBroadcast(broadcastIntent);
            }
        });

        IntentFilter intentFilter = new IntentFilter(TEST_ACTION);
        registerReceiver(mDanymicBroadcastReceiver, intentFilter);
    }

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

 2.其他注意点

广播也有ANR的限定时间，10s。10s内onReceive()如果仍没处理完，就会报ANR。所以对于耗时的操作，可以通过intent，启动其他组件或服务进行处理。

三、有序广播

上面基本用法里讲到的是普通广播。某些特定场景，需要用到有序广播，有序广播 可以根据设定好的优先级，依次处理。可以传参数，可以中断后续广播接收器的处理等操作。

注意点：

1.优先级的设置：静态注册的通过<intent-filter android:priority="">设置，动态注册通过intentFilter1.setPriority(100)。  优先级的值范围是-1000~1000。

setPriority
Added in API level 1
fun setPriority(priority: Int): Unit
Modify priority of this filter. This only affects receiver filters. The priority of activity filters are set in XML and cannot be changed programmatically. 
The default priority is 0. Positive values will be before the default, lower values will be after it. Applications should use a value that 
is larger than SYSTEM_LOW_PRIORITY and smaller than SYSTEM_HIGH_PRIORITY .
SYSTEM_LOW_PRIORITY Value: -1000
SYSTEM_HIGH_PRIORITY Value: 1000

2.有序广播 可以向低优先级的广播接收器传递数据，也可以终止传播。下面的例子有相关操作。

主要代码如下：

import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity {
    final private String TEST_ACTION = "com.flx.testBroadcastReceiver.TEST_BROADCAST_RECEIVER";
    private MyBroadcast1 mMyBroadcast1  =  new MyBroadcast1();
    private MyBroadcast2 mMyBroadcast2  =  new MyBroadcast2();
    private MyBroadcast3 mMyBroadcast3  =  new MyBroadcast3();

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

        Button sendBroadcastBtn = findViewById(R.id.send_broadcast_btn);
        sendBroadcastBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.d("flx_broadcast", "click");
                Intent broadcastIntent = new Intent();
                broadcastIntent.setAction(TEST_ACTION);
                broadcastIntent.putExtra("testkey", "testval");
//                broadcastIntent.setPackage("com.flx.testBroadcastReceiver");
//                sendBroadcast(broadcastIntent);
                sendOrderedBroadcast(broadcastIntent, null);
            }
        });

        IntentFilter intentFilter1 = new IntentFilter(TEST_ACTION);
        intentFilter1.setPriority();
        registerReceiver(mMyBroadcast1, intentFilter1);

        IntentFilter intentFilter2 = new IntentFilter(TEST_ACTION);
        intentFilter2.setPriority();
        registerReceiver(mMyBroadcast2, intentFilter2);

        IntentFilter intentFilter3 = new IntentFilter(TEST_ACTION);
        intentFilter3.setPriority();
        registerReceiver(mMyBroadcast3, intentFilter3);
    }

    @Override
    protected void onDestroy() {
        unregisterReceiver(mMyBroadcast1);
        unregisterReceiver(mMyBroadcast2);
        unregisterReceiver(mMyBroadcast3);
        super.onDestroy();
    }

    public class MyBroadcast1 extends BroadcastReceiver{
        @Override
        public void onReceive(Context context, Intent intent) {
            Log.d("flx_broadcast", "MyBroadcast1 onReceive:" );
        }
    }

    public class MyBroadcast2 extends BroadcastReceiver{
        @Override
        public void onReceive(Context context, Intent intent) {
            Log.d("flx_broadcast", "MyBroadcast2 onReceive:"+getResultData());
            abortBroadcast();
        }
    }

    public class MyBroadcast3 extends BroadcastReceiver{
        @Override
        public void onReceive(Context context, Intent intent) {
            setResultData("MyBroadcast3 set string is aaaa");
            Log.d("flx_broadcast", "MyBroadcast3 onReceive:" );
        }
    }
}

这里点击后打印出的log如下：

2019-07-31 05:17:27.459 26243-26243/com.flx.testBroadcastReceiver D/flx_broadcast: click
2019-07-31 05:17:27.486 26243-26243/com.flx.testBroadcastReceiver D/flx_broadcast: MyBroadcast3 onReceive:
2019-07-31 05:17:27.495 26243-26243/com.flx.testBroadcastReceiver D/flx_broadcast: MyBroadcast2 onReceive:MyBroadcast3 set string is aaaa

MyBroadcast3设置的优先级最高300，其次是MyBroadcast2 200,MyBroadcast1 100。由于MyBroadcast3中通过setResultData()设置了数据传到了MyBroadcast2，MyBroadcast2中abortBroadcast()停止了传播。所以log如上。

把setResultData()和abortBroadcast()注释掉后，就完全按照优先级先后执行了。log如下。

2019-07-31 05:23:15.840 26634-26634/com.flx.testBroadcastReceiver D/flx_broadcast: click
2019-07-31 05:23:15.872 26634-26634/com.flx.testBroadcastReceiver D/flx_broadcast: MyBroadcast3 onReceive:
2019-07-31 05:23:15.889 26634-26634/com.flx.testBroadcastReceiver D/flx_broadcast: MyBroadcast2 onReceive:null
2019-07-31 05:23:15.897 26634-26634/com.flx.testBroadcastReceiver D/flx_broadcast: MyBroadcast1 onReceive: