博客

我们平时最经常使用的是sendBroadcast,就是把一个Intent广播出去。今天我在看wifi的时候，还发现了sendStickyBroadcast。官方文档是这样写的：

public abstract void sendStickyBroadcast (Intent intent)

Since: API Level 1

Perform a sendBroadcast(Intent) that is “sticky,” meaning the Intent you are sending stays around after the broadcast is complete, so that others can quickly retrieve that data through the return value of registerReceiver(BroadcastReceiver, IntentFilter). In all other ways, this behaves the same as sendBroadcast(Intent).


You must hold the BROADCAST_STICKY permission in order to use this API. If you do not hold that permission, SecurityException will be thrown.

Parameters

intent The Intent to broadcast; all receivers matching this Intent will receive the broadcast, and

the Intent will be held to be re-broadcast to future receivers.

光从字面的意思是很难理解的。只有你写例子才会明白的。

       
        package
       
       com.android.testbroadcast;

       
        import
       
       android.app.Activity;
       
        import
       
       android.content.Context;
       
        import
       
       android.content.Intent;
       
        import
       
       android.os.Bundle;
       
        import
       
       android.view.View;
       
        import
       
       android.view.View.OnClickListener;
       
        import
       
       android.widget.Button;

       
        public
       
       
        class
       
       MainActivity
       
        extends
       
       Activity {
       Button btnSendi;
       Button btnSends;
       Button btnStart;
       Context mContext;
       
        /** Called when the activity is first created. */
       
        @Override
       
        public
       
       
        void
       
       onCreate(Bundle savedInstanceState) {
       
        super
       
       .onCreate(savedInstanceState);
       setContentView(R.layout.main);
       btnSendi=(Button) findViewById(R.id.sendi);
       btnSends=(Button) findViewById(R.id.sends);
       btnStart=(Button) findViewById(R.id.start);
       mContext=getApplicationContext();
       btnSendi.setOnClickListener(
       
        new
       
       OnClickListener(){

       
        @Override
       
        public
       
       
        void
       
       onClick(View v) {
       
        // TODO Auto-generated method stub
       Intent intent =
       
        new
       
       Intent();
       intent.setAction(
       
        “com.android.my.action”
       
       );
       intent.setFlags(
       
        1
       
       );
       mContext.sendBroadcast(intent);
       }

       });

       btnStart.setOnClickListener(
       
        new
       
       OnClickListener(){

       
        @Override
       
        public
       
       
        void
       
       onClick(View v) {
       
        // TODO Auto-generated method stub
       Intent intent =
       
        new
       
       Intent(MainActivity.
       
        this
       
       ,ReceiverActivity.
       
        class
       
       );

       startActivity(intent);
       }

       });

       btnSends.setOnClickListener(
       
        new
       
       OnClickListener(){

       
        @Override
       
        public
       
       
        void
       
       onClick(View v) {
       
        // TODO Auto-generated method stub
       Intent intent =
       
        new
       
       Intent();
       intent.setAction(
       
        “com.android.my.action.sticky”
       
       );
       intent.setFlags(
       
        2
       
       );
       mContext.sendStickyBroadcast(intent);
       }

       });
       }
       }

       
        package
       
       com.android.testbroadcast;

       
        import
       
       android.app.Activity;
       
        import
       
       android.content.BroadcastReceiver;
       
        import
       
       android.content.Context;
       
        import
       
       android.content.Intent;
       
        import
       
       android.content.IntentFilter;
       
        import
       
       android.net.wifi.WifiManager;
       
        import
       
       android.os.Bundle;
       
        import
       
       android.view.View;
       
        import
       
       android.view.View.OnClickListener;
       
        import
       
       android.widget.Button;

       
        public
       
       
        class
       
       ReceiverActivity
       
        extends
       
       Activity {
       
        private
       
       IntentFilter mIntentFilter;

       
        /** Called when the activity is first created. */
       
        @Override
       
        public
       
       
        void
       
       onCreate(Bundle savedInstanceState) {
       
        super
       
       .onCreate(savedInstanceState);
       setContentView(R.layout.main);
       mIntentFilter =
       
        new
       
       IntentFilter();
       mIntentFilter.addAction(
       
        “com.android.my.action”
       
       );
       mIntentFilter.addAction(
       
        “com.android.my.action.sticky”
       
       );


       }
       
        private
       
       BroadcastReceiver mReceiver =
       
        new
       
       BroadcastReceiver() {

       
        @Override
       
        public
       
       
        void
       
       onReceive(Context context, Intent intent) {
       
        final
       
       String action = intent.getAction();
       System.out.println(
       
        “action”
       
       +action);

       }
       };

       
        @Override
       
        protected
       
       
        void
       
       onResume() {
       
        // TODO Auto-generated method stub
       
        super
       
       .onResume();
       registerReceiver(mReceiver, mIntentFilter);
       }

       
        @Override
       
        protected
       
       
        void
       
       onPause() {
       
        // TODO Auto-generated method stub
       
        super
       
       .onPause();
       unregisterReceiver(mReceiver);
       }


       }

在MainActivity里面会有sendBroadcast和sendStickyBroacat.在ReceverActivity里面通 过BroadcastReceiver来接收这两个消息，在ReceiverActivity里是通过代码来注册Recevier而不是在 Manifest里面注册的。所以通过sendBroadcast中发出的intent在ReceverActivity不处于onResume状态是无 法接受到的，即使后面再次使其处于该状态也无法接受到。而sendStickyBroadcast发出的Intent当ReceverActivity重 新处于onResume状态之后就能重新接受到其Intent.这就是the Intent will be held to be re-broadcast to future receivers这句话的表现。就是说sendStickyBroadcast发出的最后一个Intent会被保留，下次当Recevier处于活跃的 时候，又会接受到它。