This Handler class should be static or leaks might occur Android

首先解释下这句话This Handler class should be static or leaks might occur，大致意思就是说：Handler类应该定义成静态类，否则可能导致内存泄露。

具体如何解决，在国外有人提出，如下：

Issue: Ensures that Handler classes do not hold on to a reference to an outer class

In Android, Handler classes should be static or leaks might occur. Messages enqueued on the application thread's MessageQueue also retain their target Handler. If the Handler is an inner class, its outer class will be retained as well. To avoid leaking the outer class, declare the Handler as a static nested class with a WeakReference to its outer class.

大体翻译如下:

Handler 类应该应该为static类型，否则有可能造成泄露。在程序消息队列中排队的消息保持了对目标Handler类的应用。如果Handler是个内部类，那 么它也会保持它所在的外部类的引用。为了避免泄露这个外部类，应该将Handler声明为static嵌套类，并且使用对外部类的弱应用。

使用范例：

1. static
   class MyHandler extends Handler {
2.                 WeakReference<PopupActivity> mActivity;
3.  
    
4.                 MyHandler(PopupActivity activity) {
5.                         mActivity = new WeakReference<PopupActivity>(activity);
6.                 }
7.  
    
8.                 @Override
9.                 public
   void handleMessage(Message msg) {
10.                         PopupActivity theActivity = mActivity.get();
11.                         switch (msg.what) {
12.                         case 0:
13.                                 theActivity.popPlay.setChecked(true);
14.                                 break;
15.                         }
16.                 }
17.         };
18.  
     
19.         MyHandler ttsHandler = new MyHandler(this);
20.         private Cursor mCursor;
21.  
     
22.         private
    void test() {
23.                 ttsHandler.sendEmptyMessage(0);
24.         }

原文：http://www.cnblogs.com/savagemorgan/archive/2013/01/23/2872371.html

疑问：是否有其它解决方法？

这个提示就是由于Handler的直接引用会导致相关的Activity、Service等无法被GC。如果这么弱应用的话，会出现空指针，有其它解决方法？

抽时间研究下。

==================================================================================================================================

原始代码：

1. public
   class MainActivity extends Activity {
2.  
3.    private
   static
   int urlIndex = 0;
4.    private
   final
   static String TAG = MainActivity.class.getSimpleName();
5.    private
   static
   final String[] url = {
6.          "http://vdn.apps.cntv.cn/api/getLiveUrlCommonRedirectApi.do?channel=pa://cctv_p2p_hdcctv1&type=ipad",
7.          "http://74.82.62.53:1935/liverepeater/13.stream/playlist.m3u8", "http://rtmp.cntv.lxdns.com/live/cctv3/playlist.m3u8", };
8.  
9.    private
   static
   final
   int MSG_PLAY = 100;
10.    private
    static
    final
    int MSG_RUN_ADB = 101;
11.    Handler playHandler = new Handler() {
12.       @Override
13.       public
    void handleMessage(Message msg) {
14.          switch (msg.what) {
15.          case MSG_PLAY:
16.             urlIndex = urlIndex > url.length - 1 ? 0 : urlIndex;
17.             videoView.setVideoPath(url[urlIndex]);
18.             ++urlIndex;
19.             break;
20.          case MSG_RUN_ADB:
21.             killMediaServer();
22.             break;
23.          }
24.       }
25.    };
26.  
27.  
28.  
29.    @Override
30.    protected
    void onCreate(Bundle savedInstanceState) {
31.       super.onCreate(savedInstanceState);
32.       requestWindowFeature(Window.FEATURE_NO_TITLE);
33.       HHVideoView.create();
34.  
35.       setContentView(R.layout.activity_main);
36.       videoView = ((HHVideoView) findViewById(R.id.videoView));
37.       videoView.setOnPreparedListener(mPreparedListener);
38.       videoView.setOnCompletionListener(mCompletionListener);
39.       videoView.setOnErrorListener(mOnErrorListener);
40.  
41.       playHandler.sendEmptyMessage(MSG_PLAY);
42.  
43.    }
44.  
45.    private HHVideoView videoView = null;
46.    private MediaPlayer.OnPreparedListener mPreparedListener = new MediaPlayer.OnPreparedListener() {
47.       public
    void onPrepared(MediaPlayer paramMediaPlayer) {
48.          // playerHandler.sendEmptyMessage(uiAction.MEDIAPLAYER_ONPREPAREED);
49.          videoView.start();
50.       }
51.    };
52.  
53.    private MediaPlayer.OnCompletionListener mCompletionListener = new MediaPlayer.OnCompletionListener() {
54.       public
    void onCompletion(MediaPlayer paramMediaPlayer) {
55.  
56.       }
57.    };
58.    private MediaPlayer.OnErrorListener mOnErrorListener = new MediaPlayer.OnErrorListener() {
59.       public
    boolean onError(MediaPlayer paramMediaPlayer, int paramInt1, int paramInt2) {
60.  
61.          return
    false;
62.       }
63.    };
64.  
65.    @Override
66.    public
    boolean onCreateOptionsMenu(Menu menu) {
67.       // Inflate the menu; this adds items to the action bar if it is present.
68.       return
    true;
69.    }
70.  
71.    public
    boolean onKeyDown(int keyCode, KeyEvent event) {
72.       if (event.getAction() == KeyEvent.ACTION_DOWN) {
73.          switch (keyCode) {
74.  
75.          case KeyEvent.KEYCODE_0:
76.  
77.             playHandler.sendEmptyMessage(MSG_RUN_ADB);
78.             break;
79.  
80.          case KeyEvent.KEYCODE_DPAD_DOWN:
81.          case KeyEvent.KEYCODE_DPAD_UP:
82.  
83.             playHandler.sendEmptyMessage(MSG_PLAY);
84.             break;
85.          }
86.       }
87.       return
    super.onKeyDown(keyCode, event);
88.  
89.    }
90.  
91. }

修改后的代码：

1. //activity code
2. public
   class MainActivity extends Activity {
3.  
4.    private
   static
   int urlIndex = 0;
5.    private
   final
   static String TAG = MainActivity.class.getSimpleName();
6.    private
   static
   final String[] url = {
7.          "http://vdn.apps.cntv.cn/api/getLiveUrlCommonRedirectApi.do?channel=pa://cctv_p2p_hdcctv1&type=ipad",
8.          "http://74.82.62.53:1935/liverepeater/13.stream/playlist.m3u8", "http://rtmp.cntv.lxdns.com/live/cctv3/playlist.m3u8", };
9.  
10.    PlayHandler playHandler ;
11.  
12.  
13.  
14.    @Override
15.    protected
    void onCreate(Bundle savedInstanceState) {
16.       super.onCreate(savedInstanceState);
17.       requestWindowFeature(Window.FEATURE_NO_TITLE);
18.       HHVideoView.create();
19.  
20.       setContentView(R.layout.activity_main);
21.       videoView = ((HHVideoView) findViewById(R.id.videoView));
22.       videoView.setOnPreparedListener(mPreparedListener);
23.       videoView.setOnCompletionListener(mCompletionListener);
24.       videoView.setOnErrorListener(mOnErrorListener);
25.  
26.       playHandler.sendEmptyMessage(PlayHandler.MSG_PLAY);
27.  
28.    }
29.  
30.    private HHVideoView videoView = null;
31.    private MediaPlayer.OnPreparedListener mPreparedListener = new MediaPlayer.OnPreparedListener() {
32.       public
    void onPrepared(MediaPlayer paramMediaPlayer) {
33.          // playerHandler.sendEmptyMessage(uiAction.MEDIAPLAYER_ONPREPAREED);
34.          videoView.start();
35.       }
36.    };
37.  
38.    private MediaPlayer.OnCompletionListener mCompletionListener = new MediaPlayer.OnCompletionListener() {
39.       public
    void onCompletion(MediaPlayer paramMediaPlayer) {
40.  
41.       }
42.    };
43.    private MediaPlayer.OnErrorListener mOnErrorListener = new MediaPlayer.OnErrorListener() {
44.       public
    boolean onError(MediaPlayer paramMediaPlayer, int paramInt1, int paramInt2) {
45.  
46.          return
    false;
47.       }
48.    };
49.  
50.    @Override
51.    public
    boolean onCreateOptionsMenu(Menu menu) {
52.       // Inflate the menu; this adds items to the action bar if it is present.
53.       return
    true;
54.    }
55.  
56.    public
    boolean onKeyDown(int keyCode, KeyEvent event) {
57.       if (event.getAction() == KeyEvent.ACTION_DOWN) {
58.          switch (keyCode) {
59.  
60.          case KeyEvent.KEYCODE_0:
61.  
62.             playHandler.sendEmptyMessage(PlayHandler.MSG_RUN_ADB);
63.             break;
64.  
65.          case KeyEvent.KEYCODE_DPAD_DOWN:
66.          case KeyEvent.KEYCODE_DPAD_UP:
67.  
68.             playHandler.sendEmptyMessage(PlayHandler.MSG_PLAY);
69.             break;
70.          }
71.       }
72.       return
    super.onKeyDown(keyCode, event);
73.  
74.    }
75.    public
    void setVideoPath() {
76.       urlIndex = urlIndex > url.length - 1 ? 0 : urlIndex;
77.       videoView.setVideoPath(url[urlIndex]);
78.       ++urlIndex;
79.    }
80. }

Handler代码：

1. //handler code
2. import java.lang.ref.WeakReference;
3.  
4. import android.os.Handler;
5. import android.os.Message;
6.  
7. /**
8.  * @author jevan
9.  * @version (1.0 at 2013-7-3)
10.  *
11.  */
12. public
    class PlayHandler extends Handler {
13.    public
    static
    final
    int MSG_PLAY = 100;
14.    public
    static
    final
    int MSG_RUN_ADB = 101;
15.    WeakReference<MainActivity> mActivity;
16.  
17.    PlayHandler(MainActivity activity) {
18.       mActivity = new WeakReference<MainActivity>(activity);
19.    }
20.  
21.    @Override
22.    public
    void handleMessage(Message msg) {
23.       MainActivity theActivity = mActivity.get();
24.       if(theActivity == null)
25.          return;
26.       switch (msg.what) {
27.       case MSG_PLAY:
28.          theActivity.setVideoPath();
29.          break;
30.       case MSG_RUN_ADB:
31.  
32.          break;
33.       }
34.    }
35. }

个人还是倾向使用独立的Handler（也就是那个外国人的解决方案），上面反映的Activity会被gc掉，导致参数空指针的问题，其实不能算问题。如果Activity被回收掉，那么Handler应该在使用之前对其状态进行判断。

个人推荐这个解决方法，当然代码会多两行。