Handler系列-sendMessage和post的区别

sendMessage和post基本一样，区别在于post的Runnable会被赋值给Message的callback，在最后调用dispatchMessage的时候，callback会被触发执行。

1.sendMessage

• 调用sendMessageDelayed发送消息

public class Handler {public final boolean sendMessage(Message msg){return sendMessageDelayed(msg, 0);}
}

2.post

• 通过Message的obtain创建Message
• 将Runnable赋值给Message的callback
• 调用sendMessageDelayed发送消息

public class Handler {public final boolean post(Runnable r){return  sendMessageDelayed(getPostMessage(r), 0);}
}

public class Handler {private static Message getPostMessage(Runnable r) {Message m = Message.obtain(); //从缓存获取Messagem.callback = r; //Runnable 赋值给Message的callbackreturn m;}
}

3.消息执行

public class Handler {public void dispatchMessage(Message msg) {if (msg.callback != null) {//post会走这里，因为它callback不为nullhandleCallback(msg);} else {if (mCallback != null) {if (mCallback.handleMessage(msg)) {return;}}handleMessage(msg);//sendMessage会走这里，调用Handler的handleMessage}}private static void handleCallback(Message message) {message.callback.run();//post的Runnable执行}
}