理解Android消息处理系统 -- Handler & Message & Looper & ThreadLocal

 

2014-2-8号补充：

今天又看Handler的原理，又有更深的理解，发现每次看都会有更进一步的理解。

有几个类有必要看看：

Handler, Looper, HandlerThread, ThreadLocal<T>, Message, MessageQueue, Parcelable，差不多了，涉及到的东西太多了。。。
http://mobile.51cto.com/abased-375243.htm http://www.2cto.com/kf/201312/262268.html http://blog.csdn.net/gemmem/article/details/7298760 http://blog.csdn.net/stonecao/article/details/6417364 http://zhidao.baidu.com/link?url=ywXTIYeaWRbDzSSu_iuJ3xs0f6v6GqlVhNhsfsuyXsjJ8xfVdJoLTwkY8-HLvygs3njNKWeQeQZSpcgqcPvyKq
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Handler这个类我想几乎所有写过android代码的人应该都用过，你分析过它么？知道它的工作原理么？

看下Looper这个类的解释：

android.os.Looper

Class used to run a message loop for a thread. Threads by default do not have a message loop associated with them; to create one, call

prepare

in the thread that is to run the
loop, and then

loop

to have it process messages until the loop is stopped.

Most interaction with a message loop is through the

Handler

class.

This is a typical example of the implementation of a Looper thread, using the separation of

prepare

and

loop

to create an initial Handler to communicate with the Looper.

class LooperThread extends Thread {
public Handler mHandler;

public void run() {
Looper.prepare();

mHandler = new Handler() {
public void handleMessage(Message msg) {
// process incoming messages here
}
};

Looper.loop();
}
}

 

Looper  ThreadLocal<T>  MessageQueue  Message Handler 这5个类应该是必须掌握的，看了看Looper的源码，表示压力好大，涉及到好多东西：

首先看下prepare()这个方法，解释如下：

Initialize the current thread as a looper. This gives you a chance to create handlers that then reference this looper, before actually starting the loop. Be sure to call

loop()

after calling this method, and end it by calling

quit()

.

每次生成looper之前，必须调用，并通过threadloacal设置到当前线程中去。

public static final void prepare()

 

这个是UI线程的looper，通过static 变量mMainLooper来存储

public static final void prepareMainLooper() 

 

Run the message queue in this thread. Be sure to call

quit()

to end the loop.

运行消息队列：

public static final void loop()