Android handle-message的发送与处理案例详解

mHandlerThread = new HandlerThread("PBAP PCE handler", Process.THREAD_PRIORITY_BACKGROUND);
mHandlerThread.start();
//将这个线程设置为消息处理Looper线程
mConnectionHandler = new PbapClientConnectionHandler.Builder().setLooper(mHandlerThread.getLooper()).setContext(mService).setClientSM(PbapClientStateMachine.this).setRemoteDevice(mCurrentDevice).build();

/**

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

     * {@link #quit()} to end the loop.

     */

    public static void loop() {

        final Looper me = myLooper();//返回保存在调用线程TLV中的Looper对象

        if (me == null) {

            throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread.");

        }

        final MessageQueue queue = me.mQueue;//取得Looper对象的消息队列

        // 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(); // might block 取消息队列中的一个待处理消息

            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);//调用该消息的Handle,交给它的dispatchMessage函数处理
        }
    }

/**
  * Handle system messages here.
  */
public void dispatchMessage(Message msg) {
    if (msg.callback != null) {
    //Message的callback不为空，则直接调用Message的callback来处理消息
        handleCallback(msg);
    } else {
        if (mCallback != null) {
            //Handle的全局Callback不为空
            if (mCallback.handleMessage(msg)) {
                return;
            }
        }
        //调用handle子类的handleMessage来处理消息
        handleMessage(msg);
    }
}

mHandler.post(new Runnable() {
    @Override
    public void run() {
        final IBinder b = callbacks.asBinder();
    });
}