This Handler class should be static or leaks might occur

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Android中，在使用到Handler的时候，如果按如下代码编写：

	private Handler handler;
	
	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		handler = new Handler() {

			@Override
			public void handleMessage(Message msg) {
				// TODO Auto-generated method stub
				super.handleMessage(msg);
			}

		};

		handler.sendMessageDelayed(Message.obtain(), 60000);

		// just finish this activity
		finish();
	}

然后运行Android Lint工具会有一个内存泄露警告:

This Handler class should be static or leaks might occur (com.example.ta.MainActivity.1)

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

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.

原因是：

1. 当Android应用启动的时候，会先创建一个应用主线程的Looper对象，Looper实现了一个简单的消息队列，一个一个的处理里面的Message对象。主线程Looper对象在整个应用生命周期中存在。

2. 当在主线程中初始化Handler时，该Handler和Looper的消息队列关联。发送到消息队列的Message会引用发送该消息的Handler对象，这样系统可以调用 Handler#handleMessage(Message) 来分发处理该消息。

3. 在Java中，非静态(匿名)内部类会引用外部类对象。而静态内部类不会引用外部类对象。

4. 如果外部类是Activity，则会引起Activity泄露 。

当Activity finish后，延时消息会继续存在主线程消息队列中1分钟，然后处理消息。而该消息引用了Activity的Handler对象，然后这个Handler又引用了这个Activity。这些引用对象会保持到该消息被处理完，这样就导致该Activity对象无法被回收，从而导致了上面说的 Activity泄露。

要修改该问题，只需要按照Lint提示的那样，把Handler类定义为静态即可，然后通过WeakReference 来保持外部的Activity对象。

	private static class WebViewHandler extends Handler{
		
		public static final int what_pullRefreshCompleted = 1;

		private final WeakReference<WebActivity> mActivity;
		
		public WebViewHandler(WebActivity mActivity) {
			super();
			this.mActivity = new WeakReference<WebActivity>(mActivity);
		}

		@Override
		public void handleMessage(Message msg) {
			if(mActivity.get() == null)
				return;
			switch(msg.what){
				case what_pullRefreshCompleted:
					if (mActivity.get().getmPullRefreshWebView() != null)//因为该Handler为static，所以我们通过调用方法来获取外部类属性
						mActivity.get().getmPullRefreshWebView().refreshComplete();
					break;
			}
			super.handleMessage(msg);
		}
	}

This Handler class should be static or leaks might occur

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原文地址：http://blog.csdn.net/catoop/article/details/47060791