记录：Handler、HandlerThread

最新推荐文章于 2025-03-07 10:29:13 发布

Lin653

最新推荐文章于 2025-03-07 10:29:13 发布

阅读量577

点赞数

分类专栏：线程文章标签：多线程 Handler HandlerThread

本文链接：https://blog.youkuaiyun.com/u010987039/article/details/85765148

版权

线程专栏收录该内容

1 篇文章

订阅专栏

Handler

关系

一个Thread对应多个Handler，一个Thread对应一个Looper和MessageQueue
Handler与Thread共享Looper和MessageQueue
Message只是消息的载体，将会被发送到与线程绑定的唯一的MessageQueue中，并且被与线程绑定的唯一的Looper分发，被与其自身绑定的Handler消费。

调用流程

当我们调用handler.sendMessage(msg)方法发送一个Message时，实际上这个Message是发送到与当前线程绑定的一个MessageQueue中
然后与当前线程绑定的Looper将会不断的从MessageQueue中取出新的Message
调用msg.target.dispathMessage(msg)方法将消息分发到与Message绑定的handler.handleMessage()方法中。

HandlerThread

在线程(Thread)中，默认是没有Looper，需要手动添加。
官方提供HandlerThread类，方便创建一个拥有Looger实例的线程，结合Handler在子线程中执行耗时或延时等任务。

Handy class for starting a new thread that has a looper. 
The looper can then be used to create handler classes. 
Note that start() must still be called.

特点

HandlerThread本质上是一个线程类，它继承了Thread
拥有自己的消息队列，它不会干扰或阻塞UI线程
拥有自己的内部Looper对象，可以进行looper循环
通过获取HandlerThread的looper对象传递给Handler对象，可以在handleMessage方法中执行异步任务
创建HandlerThread后必须先调用HandlerThread.start()方法，Thread会先调用run方法，创建Looper对象。

使用

class MainActivity : AppCompatActivity() {

    private lateinit var handlerThread: HandlerThread
    private lateinit var handler: Handler

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        handlerThread = HandlerThread(javaClass.simpleName)
        handlerThread.start()
        handler = Handler(handlerThread.looper) {
            //处理消息
            true
        }
    }

    override fun onDestroy() {
        super.onDestroy()
        handler.removeCallbacksAndMessages(null)
        handlerThread.quit()
    }
}

退出循环

HandlerThread提供两个方法退出循环。

quit

将不在接受新的事件加入消息队列
清空MessageQueue中所有消息，无论是否是延迟消息

quitSafely

将不在接受新的事件加入消息队列
清空MessageQueue中所有的延时消息
API 18 引入
区别：清空消息之前会派发所有的非延迟消息

 /**
     * Quits the looper.
     * <p>
     * Causes the {@link #loop} method to terminate without processing any
     * more messages in the message queue.
     * </p><p>
     * Any attempt to post messages to the queue after the looper is asked to quit will fail.
     * For example, the {@link Handler#sendMessage(Message)} method will return false.
     * </p><p class="note">
     * Using this method may be unsafe because some messages may not be delivered
     * before the looper terminates.  Consider using {@link #quitSafely} instead to ensure
     * that all pending work is completed in an orderly manner.
     * </p>
     *
     * @see #quitSafely
     */
    public void quit() {
        mQueue.quit(false);
    }

    /**
     * Quits the looper safely.
     * <p>
     * Causes the {@link #loop} method to terminate as soon as all remaining messages
     * in the message queue that are already due to be delivered have been handled.
     * However pending delayed messages with due times in the future will not be
     * delivered before the loop terminates.
     * </p><p>
     * Any attempt to post messages to the queue after the looper is asked to quit will fail.
     * For example, the {@link Handler#sendMessage(Message)} method will return false.
     * </p>
     */
    public void quitSafely() {
        mQueue.quit(true);
    }