1、直接再ui线程中初始化,这种情况handlermessage会在 ui线程中执行
2、传入Looper 参数,这种情况会在ht线程中执行 handlermessage。
HandlerThread ht = new HandlerThread("handler");ht.start();Handler handler = new Handler(ht.getLooper());
步骤分析:
1、HandlerThread 继承Thread
public void run() { mTid = Process.myTid(); Looper.prepare(); synchronized (this) { mLooper = Looper.myLooper(); notifyAll(); } Process.setThreadPriority(mPriority); onLooperPrepared(); Looper.loop(); mTid = -1; }
2、在run 分别初始化 ,绑定Looper 到当前线程,并且执行looper 循环处理MessageQuene 中的message
//初始化Looper a) Looper.prepare();b) if (sThreadLocal.get() != null) { throw new RuntimeException("Only one Looper may be created per thread"); } sThreadLocal.set(new Looper());c) private Looper() { mQueue = new MessageQueue(); mRun = true; mThread = Thread.currentThread(); }//绑定 Looper 到当前线程 a) sThreadLocal.set(new Looper()); b) public void set(T value) { Thread currentThread = Thread.currentThread();//取出当前线程中的ThreadLocal.Values变量 Values values = values(currentThread); if (values == null) { values = initializeValues(currentThread); }//将Looper变量保存到ThreadLocal.Values 变量中 values.put(this, value); }c) Values values(Thread current) { return current.localValues; }//循环处理MessageLooper.looper()
所以线程ht.getLooper() 可以用 ThreadLocal 从 当前线程中获取 Looper
3 、Handler 中的MessageQuene 为 Looper中 MessageQuene 的引用 ,sendmessage将Message保存到 MessageQuene,然后 再loop中取用。
public boolean sendMessageAtTime(Message msg, long uptimeMillis) { boolean sent = false; MessageQueue queue = mQueue; if (queue != null) { msg.target = this; sent = queue.enqueueMessage(msg, uptimeMillis); } else { RuntimeException e = new RuntimeException( this + " sendMessageAtTime() called with no mQueue"); Log.w("Looper", e.getMessage(), e); } return sent; }
Handler 另外用法 在service(或者非UI线程)中调用Toast等UI操作
looper = Looper.getMainLooper();handler = new Handler(looper);handler.post(new Runnable(){ public void run() { Toast.makeText().show(); }}); 同样可以使用Activity.runOnUiThread(Runnable r);