Android 消息处理源代码分析 _消息处理

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【Android 消息处理源代码分析】 android 消息处理源代码分析（1）点击打开链接

继续接着分析剩下的类文件

Looper.java public final class Looper { final MessageQueue mQueue; //消息队列 final Thread mThread; //Looper联系的线程public static void prepare() { prepare(true); }private static void prepare(boolean quitAllowed) {//先会检查是否有Looper。若有则抛出异常。没有的话则创建一个Looper实例保存起来 if (sThreadLocal.get() != null) { throw new RuntimeException(" Only one Looper may be created per thread" ); } sThreadLocal.set(new Looper(quitAllowed)); }public static void prepareMainLooper() { prepare(false); synchronized (Looper.class) { if (sMainLooper != null) { throw new IllegalStateException(" The main Looper has already been prepared." ); } sMainLooper = myLooper(); } } //在这个线程中执行消息队列。调用quit（）停止 public static void loop() { ... final MessageQueue queue = me.mQueue; // Make sure the identity of this thread is that of the local process, // and keep track of what that identity token actually is. Binder.clearCallingIdentity(); final long ident = Binder.clearCallingIdentity(); for (; ; ) { Message msg = queue.next(); // 从消息队列中取出一条消息 if (msg == null) { // No message indicates that the message queue is quitting. return; }// This must be in a local variable, in case a UI event sets the logger Printer logging = me.mLogging; if (logging != null) { logging.println(" > > > > > Dispatching to " + msg.target + " " + msg.callback + " : " + msg.what); }msg.target.dispatchMessage(msg); //交给msg的handler分发消息处理 ... } //取出当前线程的Looper，返回空则表示当前线程没有Looper public static Looper myLooper() { return sThreadLocal.get(); } }

Handler.java public class Handler { //定义Callback接口 public interface Callback { public boolean handleMessage(Message msg); } //子类要实现的消息处理方法 public void handleMessage(Message msg) { }* Handle system messages here. */ public void dispatchMessage(Message msg) {//分发信息 if (msg.callback != null) {//若指定了msg.callback，则由它处理 handleCallback(msg); } else { if (mCallback != null) {//若指定了Handler.mCallback。则由它处理 if (mCallback.handleMessage(msg)) {//调用mCallback接口的实现方法 return; } } handleMessage(msg); 最后才调用Handler自身重载的handleMessage方法 } } 分发消息函数中，消息先会检查自身有没有处理自身的回调Runnable，若有则由它处理。若没有则会检查该handler有无自身的回调处理，若有则调用，若没有则调用自身重载的handleMessage方法//Handler的生成总是和它当前所处线程有关的，假设当前线程中没有一个Looper。则会报错。UI线程中默认有产生Looper的函数 public Handler() { this(null, false); }//使用指定的Looper（能够处理那个Looper线程中的消息）。不用默认的从当前线程中取出Looper public Handler(Looper looper) { this(looper, null, false); } ... }