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);
}
}
