sendBroadcast跟sendStickyBroadcast的区别

sendBroadcast和sendStickyBroadcast的区别

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。
Java代码

1. package com.android.testbroadcast;
   
2. 
   
3. import android.app.Activity;
   
4. import android.content.BroadcastReceiver;
   
5. import android.content.Context;
   
6. import android.content.Intent;
   
7. import android.content.IntentFilter;
   
8. import android.net.wifi.WifiManager;
   
9. import android.os.Bundle;
   
10. import android.view.View;
    
11. import android.view.View.OnClickListener;
    
12. import android.widget.Button;
    
13. 
    
14. public class ReceiverActivity extends Activity {
    
15. ? ? ? ???private IntentFilter mIntentFilter;
    
16. ? ? ? ??
    
17. ? ? /** Called when the activity is first created. */
    
18. ? ? @Override
    
19. ? ? public void onCreate(Bundle savedInstanceState) {
    
20. ? ?? ???super.onCreate(savedInstanceState);
    
21. ? ?? ???setContentView(R.layout.main);
    
22. ? ?? ???mIntentFilter = new IntentFilter();
    
23. ? ?? ???mIntentFilter.addAction("com.android.my.action");
    
24. ? ?? ???mIntentFilter.addAction("com.android.my.action.sticky");
    
25. 
    
26. ? ? ? ? ? ? ? ? ? ? ? ??
    
27. ? ? }
    
28. ? ? private BroadcastReceiver mReceiver = new BroadcastReceiver() {
    
29. 
    
30. ? ?? ???@Override
    
31. ? ?? ???public void onReceive(Context context, Intent intent) {
    
32. ? ?? ?? ?? ?final String action = intent.getAction();
    
33. ? ?? ?? ?? ?System.out.println("action"+action);
    
34. ? ?? ?? ?? ?
    
35. ? ?? ???}
    
36. ? ? };
    
37. ? ??
    
38. ? ? @Override
    
39. ? ? protected void onResume() {
    
40. ? ? ? ? ? ? // TODO Auto-generated method stub
    
41. ? ? ? ? ? ? super.onResume();
    
42. ? ? ? ? ? ? registerReceiver(mReceiver, mIntentFilter);
    
43. ? ? }
    
44. ? ??
    
45. ? ? @Override
    
46. ? ? protected void onPause() {
    
47. ? ? ? ? ? ? // TODO Auto-generated method stub
    
48. ? ? ? ? ? ? super.onPause();
    
49. ? ? ? ? ? ? unregisterReceiver(mReceiver);
    
50. ? ? }
    
51. ? ??
    
52. ? ??
    
53. }

复制代码在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。