Android学习笔记-广播机制

广播机制

广播接收器（Broadcast Receiver）

• 标准广播：是一种完全异步执行的广播，广播一旦发送，所以广播接收器都会立刻同时接收到这条广播
  
  • 完全异步
  • 效率高
  • 没有先后顺序，无法截断
• 有序广播：是一种同步执行的广播，广播发出后，同一时间只有一个广播接收器能够接收到这条广播信息，然后执行，然后继续传播
  
  • 同步执行
  • 效率不高
  • 有先后顺序，可以截断正在传递的广播

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接收系统广播

动态注册监听网络变化

• 定义一个内部类NetworkChangeReceiver,这个类继承自BroadcastReceiver的，并重写onReceive()方法

class NatworkChangeReceiver extends BroadcastReceiver{

        @Override
        public void onReceive(Context context, Intent intent) {
            Toast.makeText(context, "network changes", Toast.LENGTH_SHORT).show();
        }
    }

• 在onCreate()方法，首先先创建一个IntentFilter的实例,添加action，再创建NatworkChangeReceiver实例，最后调用registerReceiver()方法进行注册

    private IntentFilter intentFilter;
    private NatworkChangeReceiver natworkChangeReceiver;

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

• 记得，动态注册的广播接收器一定都要取消注册才行，这里我们是在onDestroy()方法调用unregisterReceiver()方法

静态注册实现开机启动

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

• 需要在AndroidManifest.xml将广播接收器的类名注册进去。

<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>

.....

<receiver android:name=".BootCompleteReceiver">
  <intent-filter>
    <action android:name="android.intent.action.BOOT_COMPLETED"/>
  </intent-filter>
</receiver>

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发送标准广播

• 接收自定义的广播

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

• 在AndroidManifest.xml中对这个广播接收器进行注册

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

• 利用按键监听去触发发送自定义广播

 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);
            }
        });

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发送有序广播

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); 标准广播
                sendOrderedBroadcast(intent,null);//有序广播
            }
        });

• 添加优先值

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

• 截断广播

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

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使用本地广播

• 获取LocalBroadcastManager实例

localBroadcastManager = LocalBroadcastManager.getInstance(this);//获取实例
......

 class LocalReceiver extends BroadcastReceiver{

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

• 注册本地广播监听器

        intentFilter = new IntentFilter();
        intentFilter.addAction("com.example,broadcasttest.LOCAL_BROADCAST");

        localReceiver = new LocalReceiver();
        localBroadcastManager.registerReceiver(localReceiver,intentFilter);

        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);//发送本地广播
            }
        });

• 取消注册

      localBroadcastManager.unregisterReceiver(localReceiver);

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