Handler 的sendEmptyMessage(int what)和sendMessage(Message msg)有啥区别?
2012-11-02 17:38
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做一个手机助手查看器,碰到里面的Handler用sendEmptyMessage(int what)发消息,其实也可以用sendMessage(Message msg)的,但两者到底有啥区别?GOOGLE一下,没有看到什么好的答案,倒是看到一个大三的家伙有模有样的分析起来了安卓类的源代码,SHIT,此刻的我真是汗颜,不过老子说得好嘛---故师者,无长无优,闻道有先后而已。哦,记错了,是韩愈说的。收到了启发,也开始看起类的源代码起来。
其实两者没区别,请看下面Handler的源代码:
/**
* Sends a Message containing only the what value.
*
* @return Returns true if the message was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean sendEmptyMessage(int what)
{
return sendEmptyMessageDelayed(what, 0);
}
就是调用了sendEmptyMessageDelayed()而已,下面看下这个方法:
/**
* Sends a Message containing only the what value, to be delivered
* after the specified amount of time elapses.
* @see #sendMessageDelayed(android.os.Message, long)
*
* @return Returns true if the message was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean sendEmptyMessageDelayed(int what, long delayMillis) {
Message msg = Message.obtain();
msg.what = what;
return sendMessageDelayed(msg, delayMillis);
}
而sendMessage(Message msg)的实现和上面一样,请看:
/**
* Pushes a message onto the end of the message queue after all pending messages
* before the current time. It will be received in {@link #handleMessage},
* in the thread attached to this handler.
*
* @return Returns true if the message was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean sendMessage(Message msg)
{
return sendMessageDelayed(msg, 0);
}
原来在sendEmptyMessageDelayed中就是构建了一个Message,然后把这个Message的what设置成sendEmptyMessage方法中的What参数即可。
一切恍然大悟!
然后,在主线程中,Looper类的loop()通过 调用: msg.target.dispatchMessage(msg),调用Hanler类的dispatchMessage(Message msg)方法,从而在主线程中处理了这个Message.
如果对Handler机制要深入了解的,请参考上面那位大三“老师”的博客文章:http://www.cnblogs.com/codingmyworld/archive/2011/09/14/2174255.html。
其实两者没区别,请看下面Handler的源代码:
/**
* Sends a Message containing only the what value.
*
* @return Returns true if the message was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean sendEmptyMessage(int what)
{
return sendEmptyMessageDelayed(what, 0);
}
就是调用了sendEmptyMessageDelayed()而已,下面看下这个方法:
/**
* Sends a Message containing only the what value, to be delivered
* after the specified amount of time elapses.
* @see #sendMessageDelayed(android.os.Message, long)
*
* @return Returns true if the message was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean sendEmptyMessageDelayed(int what, long delayMillis) {
Message msg = Message.obtain();
msg.what = what;
return sendMessageDelayed(msg, delayMillis);
}
而sendMessage(Message msg)的实现和上面一样,请看:
/**
* Pushes a message onto the end of the message queue after all pending messages
* before the current time. It will be received in {@link #handleMessage},
* in the thread attached to this handler.
*
* @return Returns true if the message was successfully placed in to the
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean sendMessage(Message msg)
{
return sendMessageDelayed(msg, 0);
}
原来在sendEmptyMessageDelayed中就是构建了一个Message,然后把这个Message的what设置成sendEmptyMessage方法中的What参数即可。
一切恍然大悟!
然后,在主线程中,Looper类的loop()通过 调用: msg.target.dispatchMessage(msg),调用Hanler类的dispatchMessage(Message msg)方法,从而在主线程中处理了这个Message.
如果对Handler机制要深入了解的,请参考上面那位大三“老师”的博客文章:http://www.cnblogs.com/codingmyworld/archive/2011/09/14/2174255.html。
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