Handle-Message的发送和处理

1、Handle,MessageQueue,Message类图

Handle: 处理消息，并提供一系列函数帮忙我们创建消息和插入消息到消息队列中

创建handle实例--PbapClientConnectionHandler

//创建一个线程

         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();

 

Looper作用：Looper的prepare函数将Looper和调用prepare的线程绑定在一起，调用线程调用loop函数处理来自该消息队列的消息。

Android 系统的消息队列和消息循环都是针对具体线程的，一个线程可以存在（当然也可以不存在）一个消息队列和一个消息循环（Looper），特定线程的消息只能分发给本线程，不能进行跨线程通讯。但是创建的工作线程默认是没有消息循环和消息队列的，如果想让该线程具有消息队列和消息循环，需要在线程中首先调用Looper.prepare()来创建消息队列，然后调用Looper.loop()进入消息循环

MessageQueue:消息队列，Handle和Looper中使用的是同一个消息队列

 

 

2、发送消息

 

3、处理消息

looper处理消息：

loop 使消息循环起作用，取消息，处理消息

    /**

     * 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 -dispatchMessage

 /**
     * 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);
        }
    }

Message.callback用法：将Runnable当做一个Message

Runnable线程处理使用实例

    mHandler.post(new Runnable() {

                    @Override

                    public void run() {

                        final IBinder b = callbacks.asBinder();

 

                });

        }