【移动开发】Handler的sendMessageAtTime()和sendEmptyMessageDelay()区别-优快云博客

本文链接：https://blog.youkuaiyun.com/manoel/article/details/40017261

本文详细探讨了移动应用开发中Handler对象的两个关键方法：sendMessageAtTime()和sendEmptyMessageDelay()。通过源码分析，揭示了它们在消息调度上的区别，帮助开发者更好地理解和运用这两个方法来实现精确的消息控制和线程间通信。

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函数原型

public boolean sendMessageAtTime (Message msg, long uptimeMillis)

Message //待发送消息
uptimeMillis //sendMessageAtTime,即在确定的时间发送这个消息，这个时间通过这个参数指定这个时间由uptimeMillis传递

这两句是等效的，都是延时1秒将消息加入列队
msgHandle.sendMessageAtTime(msg, SystemClock.uptimeMillis()+1000);
msgHandle.sendMessageDelayed(msg, 1000)

sendMessageAtTime的uptimeMillis是相对系统开机时间的绝对时间，SystemClock.uptimeMillis()是当前开机时间。

源码

    /**
     * Enqueue a message into the message queue after all pending messages
     * before (current time + delayMillis). You will receive it in
     * {@link #handleMessage}, in the thread attached to this handler.
     *  
     * @return Returns true if the message was successfully placed in to the 
     *         message queue.  Returns false on failure, usually because the
     *         looper processing the message queue is exiting.  Note that a
     *         result of true does not mean the message will be processed -- if
     *         the looper is quit before the delivery time of the message
     *         occurs then the message will be dropped.
     */
    public final boolean sendMessageDelayed(Message msg, long delayMillis)
    {
        if (delayMillis < 0) {
            delayMillis = 0;
        }
        return sendMessageAtTime(msg, SystemClock.uptimeMillis() + delayMillis);
    }

    /**
     * Enqueue a message into the message queue after all pending messages
     * before the absolute time (in milliseconds) <var>uptimeMillis</var>.
     * <b>The time-base is {@link android.os.SystemClock#uptimeMillis}.</b>
     * You will receive it in {@link #handleMessage}, in the thread attached
     * to this handler.
     * 
     * @param uptimeMillis The absolute time at which the message should be
     *         delivered, using the
     *         {@link android.os.SystemClock#uptimeMillis} time-base.
     *         
     * @return Returns true if the message was successfully placed in to the 
     *         message queue.  Returns false on failure, usually because the
     *         looper processing the message queue is exiting.  Note that a
     *         result of true does not mean the message will be processed -- if
     *         the looper is quit before the delivery time of the message
     *         occurs then the message will be dropped.
     */
    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;
    }