Android多线程及异步处理问题详细探讨

public Handler() {
mLooper = Looper.myLooper();
//当前线程的Looper，在Activity创建时，UI线程已经创建了Looper对象
//在Handler中机制中Looper是最为核心的，它一直处于循环读MessageQueue，有
//要处理的Message就将Message发送给当前的Handler实例来处理

if (mLooper == null) {
throw new RuntimeException(
“Can't create handler inside thread that has not called Looper.prepare()”);
}
//从以上可以看出，一个Handler实例必须关联一个Looper对象，否则出错

mQueue = mLooper.mQueue;
//Handler的MessageQueue，它是FIFO的吗？不是！我感觉应该是按时间先后排列
//的！Message与MessageQueue到底是啥关系？感兴趣可以研究一下源码！

mCallback = null;
}

private static final class Worker implements Runnable
{
private static final Object mLock = new Object() ;
private Looper mLooper ;

public Worker(String name)
{
final Thread thread = new Thread(null,this,name) ;
thread.setPriority(Thread.MIN_PRIORITY) ;
thread.start() ;

synchronized(mLock)
{
while(mLooper == null)
{
try
{
mLock.wait() ;
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
}
}

@Override
public void run() {
synchronized(mLock)
{
//该方法只能执行一次,一个Thread只能关联一个Looper
Looper.prepare() ;
mLooper = Looper.myLooper() ;
mLock.notifyAll() ;
}
Looper.loop() ;
}

public Looper getLooper()
{
return mLooper ;
}

public void quit()
{
mLooper.quit() ;
}
}

private final class MyHandler extends Handler
{
private long id ;

public MyHandler(Looper looper)
{
super(looper) ;
}

@Override
public void handleMessage(Message msg) {
switch(msg.what)
{
case 100 :
mTv.setText(“” + id) ;
break ;
}
}
}

public final Message obtainMessage(int what)
{
return Message.obtain(this, what);
}

public static Message obtain(Handler h, int what) {
Message m = obtain();
m.target = h;//可以看出message关联了当前的Handler
m.what = what;
return m;
}