如何停止一系列的postDelayed处理程序

Question

如何停止一系列的postDelayed处理程序

4

我有一系列的postDelayed处理程序。当用户随时点击停止按钮时，我遇到了在设置停止处理程序的方法方面的困难。

如果有人能提供帮助, 我会非常感激。谢谢。

while (!lessonIsRunning) {
        Handler handler0 = new Handler();
        handler0.postDelayed(new Runnable() {
          @Override
          public void run() {
              plate1.setVisibility(ImageView.VISIBLE);
              plate2.setVisibility(ImageView.VISIBLE);
              plate3.setVisibility(ImageView.VISIBLE);
          }
        }, 6000);

        Handler handler1 = new Handler();
        handler1.postDelayed(new Runnable() {
          @Override
          public void run() {
              apples1.setVisibility(ImageView.VISIBLE);
          }
        }, 9000);

        Handler handler2 = new Handler();
        handler2.postDelayed(new Runnable() {
          @Override
          public void run() {
              plus1.setVisibility(TextView.VISIBLE);
          }
        }, 9250);
}
public void stopLesson(View V){

}

- RBZ

2

为什么你在使用多个处理程序？为什么不使用单个处理程序？ - CommonsWare

2个回答

4

你可以给

handler0.removeCallbacksAndMessages(null);
handler1.removeCallbacksAndMessages(null);
handler2.removeCallbacksAndMessages(null);

尝试一下。文档中说明，当您提交空令牌时，所有回调和消息都将被删除。

- Blackbelt

谢谢您的快速回答！问题是当我在handler0播放时停止它，我会在handler1.removeCallbacksAndMessages(null)上得到nullPointerException。有没有一种检查处理程序状态的方法？或者您能想到的任何布尔条件？ - RBZ

问题与removeCallbacksAndMessages参数无关。可能是handler1为空。 - Blackbelt

1

@RBZ：此外，只能从处理程序的主线程（例如，主应用程序线程）调用这些方法。 - CommonsWare

1

+1，我还没有尝试过这个，但我总是更喜欢传递对象而不是null。 - Inder Kumar Rathore

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- Lena Bru · Accepted Answer

不要以匿名方式编写Runnable任务，而是必须为其定义一个名称，以便以后您将拥有一个链接以删除它：

//there is no need for multiple handlers 
//handler must be declared outside all functions, in order for you to use it everywhere. 

Handler handler = new Handler(); 
Runnable myFirstTask  = new Runnable (){
         @Override
              public void run() {
                  plate1.setVisibility(ImageView.VISIBLE);
                  plate2.setVisibility(ImageView.VISIBLE);
                  plate3.setVisibility(ImageView.VISIBLE);
              } };

    Runnable mySecondTask = new Runnable(){
        @Override
              public void run() {
                  plus1.setVisibility(TextView.VISIBLE);
              }

    };

    Runnable myThirdTask = new Runnable(){
        @Override
              public void run() {
                  apples1.setVisibility(ImageView.VISIBLE);
              } }

    //you can put different tasks on the same handler object

    while (!lessonIsRunning) {   
            handler.postDelayed(myFirstTask,6000);   
            handler.postDelayed(mySecondTask,9250);   
            handler.postDelayed(myThirdTask,9000); 
} 
public void stopLesson(View V){ 
    //notice that you don't need these, because the handlers are not recursive 
    //you don't have lines "handler.postDelayed(sameTask,someTime);" 
    //in your run Method of the runnable
 if(handler!=null){
    handler.removeCallbacks(myFirstTask);
    handler.removeCallbacks(mySecondTask); 
    handler.removeCallbacks(myThirdTask); 
    //if this method is inside onPause or onDestroy add this line as well: 
    handler=null; 

}
 }