复制代码代码如下:

publicclass LooperThread extends Thread { 
@Override 
publicvoid run() { 
// 将当前线程初始化为Looper线程 
Looper.prepare();

// ...其他处理，如实例化handler

// 开始循环处理消息队列 
Looper.loop(); 
} 
}

复制代码代码如下:

publicclass Looper { 
// 每个线程中的Looper对象其实是一个ThreadLocal，即线程本地存储(TLS)对象 
privatestaticfinal ThreadLocal sThreadLocal =new ThreadLocal(); 
// Looper内的消息队列 
final MessageQueue mQueue; 
// 当前线程 
Thread mThread; 
// 。。。其他属性

// 每个Looper对象中有它的消息队列，和它所属的线程 
private Looper() { 
mQueue =new MessageQueue(); 
mRun =true; 
mThread = Thread.currentThread(); 
}

// 我们调用该方法会在调用线程的TLS中创建Looper对象 
publicstaticfinalvoid prepare() { 
if (sThreadLocal.get() !=null) { 
// 试图在有Looper的线程中再次创建Looper将抛出异常 
thrownew RuntimeException("Only one Looper may be created per thread"); 
} 
sThreadLocal.set(new Looper()); 
} 
// 其他方法 
}

复制代码代码如下:

publicstaticfinalvoid loop() { 
Looper me = myLooper(); //得到当前线程Looper 
MessageQueue queue = me.mQueue; //得到当前looper的MQ

// 这两行没看懂= = 不过不影响理解 
Binder.clearCallingIdentity(); 
finallong ident = Binder.clearCallingIdentity(); 
// 开始循环 
while (true) { 
Message msg = queue.next(); // 取出message 
if (msg !=null) { 
if (msg.target ==null) { 
// message没有target为结束信号，退出循环 
return; 
} 
// 日志。。。 
if (me.mLogging!=null) me.mLogging.println( 
">>>>> Dispatching to "+ msg.target +"" 
+ msg.callback +": "+ msg.what 
); 
// 非常重要！将真正的处理工作交给message的target，即后面要讲的handler 
msg.target.dispatchMessage(msg); 
// 还是日志。。。 
if (me.mLogging!=null) me.mLogging.println( 
"<<<<< Finished to "+ msg.target +"" 
+ msg.callback);

// 下面没看懂，同样不影响理解 
finallong newIdent = Binder.clearCallingIdentity(); 
if (ident != newIdent) { 
Log.wtf("Looper", "Thread identity changed from 0x" 
+ Long.toHexString(ident) +" to 0x" 
+ Long.toHexString(newIdent) +" while dispatching to " 
+ msg.target.getClass().getName() +"" 
+ msg.callback +" what="+ msg.what); 
} 
// 回收message资源 
msg.recycle(); 
} 
} 
}

复制代码代码如下:

publicstaticfinal Looper myLooper() { // 在任意线程调用Looper.myLooper()返回的都是那个线程的looperreturn (Looper)sThreadLocal.get(); }

复制代码代码如下:

public Thread getThread() { return mThread; }

复制代码代码如下:

publicvoid quit() { 
// 创建一个空的message，它的target为NULL，表示结束循环消息 
Message msg = Message.obtain(); 
// 发出消息 
mQueue.enqueueMessage(msg, 0); 
} 

复制代码代码如下:

publicclass handler {

final MessageQueue mQueue; // 关联的MQ 
final Looper mLooper; // 关联的looper 
final Callback mCallback; 
// 其他属性

public Handler() { 
// 没看懂，直接略过，，， 
if (FIND_POTENTIAL_LEAKS) { 
final Class<?extends Handler> klass = getClass(); 
if ((klass.isAnonymousClass() || klass.isMemberClass() || klass.isLocalClass()) && 
(klass.getModifiers() & Modifier.STATIC) ==0) { 
Log.w(TAG, "The following Handler class should be static or leaks might occur: "+ 
klass.getCanonicalName()); 
} 
} 
// 默认将关联当前线程的looper 
mLooper = Looper.myLooper(); 
// looper不能为空，即该默认的构造方法只能在looper线程中使用 
if (mLooper ==null) { 
thrownew RuntimeException( 
"Can't create handler inside thread that has not called Looper.prepare()"); 
} 
// 重要！！！直接把关联looper的MQ作为自己的MQ，因此它的消息将发送到关联looper的MQ上 
mQueue = mLooper.mQueue; 
mCallback =null; 
}

// 其他方法 
}

复制代码代码如下:

publicclass LooperThread extends Thread { 
private Handler handler1; 
private Handler handler2;

@Override 
publicvoid run() { 
// 将当前线程初始化为Looper线程 
Looper.prepare();

// 实例化两个handler 
handler1 =new Handler(); 
handler2 =new Handler();

// 开始循环处理消息队列 
Looper.loop(); 
} 
}

复制代码代码如下:

// 此方法用于向关联的MQ上发送Runnable对象，它的run方法将在handler关联的looper线程中执行 
publicfinalboolean post(Runnable r) 
{ 
// 注意getPostMessage(r)将runnable封装成message 
return sendMessageDelayed(getPostMessage(r), 0); 
}

privatefinal Message getPostMessage(Runnable r) { 
Message m = Message.obtain(); //得到空的message 
m.callback = r; //将runnable设为message的callback， 
return m; 
}

publicboolean sendMessageAtTime(Message msg, long uptimeMillis) 
{ 
boolean sent =false; 
MessageQueue queue = mQueue; 
if (queue !=null) { 
msg.target =this; // message的target必须设为该handler！ 
sent = queue.enqueueMessage(msg, uptimeMillis); 
} 
else { 
RuntimeException e =new RuntimeException( 
this+" sendMessageAtTime() called with no mQueue"); 
Log.w("Looper", e.getMessage(), e); 
} 
return sent; 
}

复制代码代码如下:

msg.target.dispatchMessage(msg);

复制代码代码如下:

// 处理消息，该方法由looper调用 
publicvoid dispatchMessage(Message msg) { 
if (msg.callback !=null) { 
// 如果message设置了callback，即runnable消息，处理callback！ 
handleCallback(msg); 
} else { 
// 如果handler本身设置了callback，则执行callback 
if (mCallback !=null) { 
/* 这种方法允许让activity等来实现Handler.Callback接口，避免了自己编写handler重写handleMessage方法。见http://alex-yang-xiansoftware-com.iteye.com/blog/850865 */ 
if (mCallback.handleMessage(msg)) { 
return; 
} 
} 
// 如果message没有callback，则调用handler的钩子方法handleMessage 
handleMessage(msg); 
} 
}

// 处理runnable消息 
privatefinalvoid handleCallback(Message message) { 
message.callback.run(); //直接调用run方法！ 
} 
// 由子类实现的钩子方法 
publicvoid handleMessage(Message msg) { 
}

复制代码代码如下:

publicclass TestDriverActivity extends Activity { 
private TextView textview;

@Override 
protectedvoid onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.main); 
textview = (TextView) findViewById(R.id.textview); 
// 创建并启动工作线程 
Thread workerThread =new Thread(new SampleTask(new MyHandler())); 
workerThread.start(); 
}

publicvoid appendText(String msg) { 
textview.setText(textview.getText() +"\n"+ msg); 
}

class MyHandler extends Handler { 
@Override 
publicvoid handleMessage(Message msg) { 
String result = msg.getData().getString("message"); 
// 更新UI 
appendText(result); 
} 
} 
}

复制代码代码如下:

publicclass SampleTask implements Runnable { 
privatestaticfinal String TAG = SampleTask.class.getSimpleName(); 
Handler handler;

public SampleTask(Handler handler) { 
super(); 
this.handler = handler; 
}

@Override 
publicvoid run() { 
try { // 模拟执行某项任务，下载等 
Thread.sleep(5000); 
// 任务完成后通知activity更新UI 
Message msg = prepareMessage("task completed!"); 
// message将被添加到主线程的MQ中 
handler.sendMessage(msg); 
} catch (InterruptedException e) { 
Log.d(TAG, "interrupted!"); 
}

}

private Message prepareMessage(String str) { 
Message result = handler.obtainMessage(); 
Bundle data =new Bundle(); 
data.putString("message", str); 
result.setData(data); 
return result; 
}

}