Android学习笔记之广播机制（1）

     <p>广播接收者（BroadcastReceiver）用于异步接收广播Intent，广播Intent的发送是通过调用Context.sendBroadcast()、Context.sendOrderedBroadcast()或者Context.sendStickyBroadcast()来实现的。通常一个广播Intent可以被订阅了此Intent的多个广播接收者所接收。</p>    <p>广播机制：</p>    <p><img title="Android学习笔记之广播机制（1） " border="0" alt="Android学习笔记之广播机制（1） " src="https://simg.open-open.com/show/4b33d6c3ef8169ca8d3a117a168b7e65.jpg" width="500" height="283" /></p>    <p>要实现一个广播接收者方法如下：</p>    <p><br /> 界面：</p>    <pre class="brush:java; toolbar: true; auto-links: false;">package mars.testbc;  import android.app.Activity; import android.content.Intent; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button;  public class TestActivity extends Activity {     /** Called when the activity is first created. */  private Button sendButton;     @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.testreceiver);         sendButton = (Button)findViewById(R.id.sendButton);         sendButton.setOnClickListener(new BroadcastListener());     }     class BroadcastListener implements OnClickListener{    public void onClick(View v) {    Intent intent = new Intent();    intent.setAction(Intent.ACTION_EDIT);    TestActivity.this.sendBroadcast(intent);   }           } }</pre>    <p><br /> 第一步：要想实现一个广播机制，就必须实现一个类，这个类继承于BroadcastReceiver并重写onReceive()方法。</p>    <pre class="brush:java; toolbar: true; auto-links: false;">package mars.testbc;  import android.content.BroadcastReceiver; import android.content.Context; import android.content.Intent;  public class TestReceiver extends BroadcastReceiver{   public TestReceiver(){   System.out.println("TestReceiver");  }  @Override  public void onReceive(Context context, Intent intent) {   System.out.println("onReceive");  } }</pre>    <p>事件响应的实现应在onReceive方法中实现。</p>    <p>第二步：订阅感兴趣的广播Intent，订阅方法有两种：<br /> 第一种：使用代码进行订阅<br /> IntentFilter filter = new IntentFilter("android.provider.Telephony.SMS_RECEIVED");<br /> IncomingSMSReceiver receiver = new IncomingSMSReceiver();<br /> registerReceiver(receiver, filter);<br /> 第二种：在AndroidManifest.xml文件中的<application>节点里进行注册:<br /> <intent-filter>是一个过滤器。</p>    <p>在发送广播过程中，如果某个BroadCastReceiver的Action和这里的Action相符合，则启动，接受广播。</p>    <pre class="brush:java; toolbar: true; auto-links: false;"><receiver android:name=".TestReceiver">    <intent-filter>     <action android:name="android.intent.action.PICK" />    </intent-filter>   </receiver></pre>    <p><br /> 生命周期：</p>    <p>每次广播到来时,会重新创建BroadcastReceiver对象,并且调用onReceive()方法,执行完以后,该对象即被销毁.</p>    <p>当onReceive()方法在10秒内没有执行完毕，Android会认为该程序无响应.所以在</p>    <p>BroadcastReceiver里不能做一些比较耗时的操作,否侧会弹出ANR(Application No </p>    <p>Response)的对话框.。</p>    <p> </p>