android – Handler.dispatchMessage(msg)和Handler.sendMessage(msg)之间的区别

当我使用Handler.dispatchMessage(msg)时,handleMessage(Message msg)将在新线程上运行,但是当我使用Handler.sendMessage(msg)时,handleMessage(Message msg)将在主线程上运行,谁可以告诉我和他们之间的区别.

谢谢！

演示：

public class MainActivity extends Activity
{
private String TAG = "MainActivity";
private Handler mHandler = new Handler()
{
    @Override
    public void handleMessage(Message msg)
    {
        Log.i(TAG,"Handler:" + Thread.currentThread().getId() + "&arg1=" + msg.arg1);
        super.handleMessage(msg);
    }

};

@Override
public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    Log.i(TAG,"Main:" + Thread.currentThread().getId());
    testMethod();
}

private void testMethod()
{
    Thread thread = new Thread()
    {
        @Override
        public void run()
        {
            Log.i(TAG,"Thread:" + Thread.currentThread().getId());
            Message msg = mHandler.obtainMessage();
            msg.arg1 = 1;
            mHandler.dispatchMessage(msg);
            Message msg2 = mHandler.obtainMessage();
            msg2.arg1 = 2;
            mHandler.sendMessage(msg2);
        }

    };
    thread.start();
}

}

输出：

04-19 11:32:10.452: INFO/MainActivity(774): Main:1
04-19 11:32:10.488: INFO/MainActivity(774): Thread:8
04-19 11:32:10.492: INFO/MainActivity(774): Handler:8&arg1=1
04-19 11:32:10.635: INFO/MainActivity(774): Handler:1&arg1=2

解决方法

mHandler.dispatchMessage(msg)就像直接调用handleMessage(Message msg),我不知道什么时候会有用. Handlers的重点是能够向其他线程发送消息.这就是你用sendMessage做的事情.

编辑：你可以看到它只是为你调用handleMessage().

/**
 * Handle system messages here.
 */
public void dispatchMessage(Message msg) {
    if (msg.callback != null) {
        // callback = the Runnable you can post "instead of" Messages.
        msg.callback.run();
    } else {
        if (mCallback != null) {
            if (mCallback.handleMessage(msg)) {
                return;
            }
        }
        handleMessage(msg);
    }
}