如果一个Activity有多个handler时候，handler1发送的消息是否会被handler2接收，同理handler2发送的消息是否会被handler1接收？
答案是：不会，一句话谁发送的消息，谁处理，为什么，因为每个Message消息都会绑定一个target来指定这个消息由谁来处理。

1 Message消息在被发送时会被绑定Handler

追溯源码发现，无论使用Handler的哪个方法来发送消息，最终都会调用到下面方法来发送，在这里 msg对象会被绑定target，而这里的值为this，正是发送消息的Handler的本身，

private boolean enqueueMessage(MessageQueue queue, Message msg, long uptimeMillis) {
    msg.target = this;
    if (mAsynchronous) {
        msg.setAsynchronous(true);
    }
    return queue.enqueueMessage(msg, uptimeMillis);
}
2 Message消息在被处理的时候

追溯源码

 public static void loop() {
        final Looper me = myLooper();
        if (me == null) {
            throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread.");
        }
        final MessageQueue queue = me.mQueue;

        // 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
            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);

            if (logging != null) {
                logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);
            }

            // Make sure that during the course of dispatching the
            // identity of the thread wasn't corrupted.
            final long newIdent = Binder.clearCallingIdentity();
            if (ident != newIdent) {
                Log.wtf(TAG, "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);
            }

            msg.recycleUnchecked();
        }
    }

msg.target.dispatchMessage(msg); 关键的这一句，msg调用了自身绑定的target的dispatchMessage方法来处理消息，而这里的target正是msg在被发送的时候所绑定的handler.