Android的Handler在活动被销毁后仍然持续运行一段时间。

huangapple
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英文:

Android Handler keeps running for a while even after the activity has been destroyed

问题

我读到handler.postDelayed方法有助于暂停任务一段时间。因此，我将其写入光线传感器中，以便传感器每隔2秒钟检测一次光线，以节省电池寿命：

  1. public class MainActivity extends Activity {
  3.     @Override
  4.     protected void onCreate(Bundle savedInstanceState) {
  5.         super.onCreate(savedInstanceState);
  6.         setContentView(R.layout.activity_main);
  8.         SensorManager sm = (SensorManager) getSystemService(SENSOR_SERVICE);
  9.         Sensor light = sm.getDefaultSensor(Sensor.TYPE_LIGHT);
  10.         SensorEventListener listener;
  12.         if (light != null) {
  13.             final Handler handler = new Handler();
  14.             final Runnable task = new Runnable() {
  15.                 @Override
  16.                 public void run() {
  17.                     sm.registerListener(listener, light, SensorManager.SENSOR_DELAY_NORMAL);
  18.                 }
  19.             };
  21.             listener = new SensorEventListener() {
  22.                 @Override
  23.                 public void onAccuracyChanged(Sensor sensor, int accuracy) {
  24.                     Toast.makeText(MainActivity.this, "accuracy changed!", Toast.LENGTH_SHORT).show();
  25.                 }
  27.                 @Override
  28.                 public void onSensorChanged(SensorEvent event) {
  29.                     sm.unregisterListener(listener, light);
  31.                     // 在此处处理接收到的传感器光线值，即event.values[0]
  33.                     handler.postDelayed(task, 2000);
  34.                 }
  35.             };
  36.         }
  37.     }
  39.     @Override
  40.     protected void onPause() {
  41.         super.onPause();
  42.         sm.unregisterListener(listener, light);
  43.     }
  45.     @Override
  46.     protected void onResume() {
  47.         super.onResume();
  48.         sm.registerListener(listener, light, SensorManager.SENSOR_DELAY_NORMAL);
  49.     }
  51.     @Override
  52.     protected void onStop() {
  53.         super.onStop();
  54.         sm.unregisterListener(listener, light);
  55.     }
  57.     @Override
  58.     protected void onDestroy() {
  59.         super.onDestroy();
  60.         sm.unregisterListener(listener, light);
  61.     }
  62. }

起初，它似乎正常工作。但我发现每次退出应用程序时，它会持续大约20到30秒钟检测光线，就好像活动仍然打开一样。我做错了什么？我甚至添加了onStop和onDestroy方法，只是为了确保它正确关闭。

英文:

I read that the handler.postDelayed method helps pause a task for any amount of time. So I wrote it into the light sensor so that the sensor only detects light every 2 seconds, in order to save battery life:

  1. public class MainActivity extends Activity {
  4.     @Override
  5.     protected void onCreate(Bundle savedInstanceState) {
  7.     super.onCreate(savedInstanceState);
  8.     setContentView(R.layout.activity_main);
  10.     SensorManager sm = (SensorManager) getSystemService(SENSOR_SERVICE);
  11.     Sensor light = sm.getDefaultSensor(Sensor.TYPE_LIGHT);
  12.     SensorEventListener listener;
  14.     if (light != null) {
  16.         final Handler handler = new Handler();
  17.         final Runnable task = new Runnable() {
  18.             @Override
  19.             public void run() {
  20.                 sm.registerListener(listener, light, SensorManager.SENSOR_DELAY_NORMAL);
  21.             }
  22.         };
  24.         listener = new SensorEventListener() {
  26.             @Override
  27.             public void onAccuracyChanged(Sensor sensor, int accuracy) {
  28.                 Toast.makeText(MainActivity.this, "accuracy changed!", Toast.LENGTH_SHORT).show();
  29.             }
  31.             @Override
  32.             public void onSensorChanged(SensorEvent event) {
  34.                 sm.unregisterListener(listener, light);
  36.                 // Do the stuff here with the received sensor light value, which is event.values[0]
  37.                 
  38.                 handler.postDelayed(task, 2000);
  39.             }
  40.         };
  42.     }
  44.     @Override
  45.     protected void onPause() {
  46.         super.onPause();
  47.         sm.unregisterListener(listener, light);
  48.     }
  50.     @Override
  51.     protected void onResume() {
  52.         super.onResume();
  53.         sm.registerListener(listener, light, SensorManager.SENSOR_DELAY_NORMAL);
  54.     }
  56.     @Override
  57.     protected void onStop() {
  58.         super.onStop();
  59.         sm.unregisterListener(listener, light);
  60.     }
  62.     @Override
  63.     protected void onDestroy() {
  64.         super.onDestroy();
  65.         sm.unregisterListener(listener, light);
  66.     }
  67. }

At first it seemed to work fine. But I found that every time I exit the app it kept detecting the light for like 20 to 30 seconds as if the activity was still open. What am I doing wrong? I even added both the onStop and onDestroy methods just to be sure it was closing correctly.

答案1

得分: 2

在您的活动的 onDestroy() 中，清除您的处理程序，如下所示：

  1. handler.removeCallbacksAndMessages(null);

这样就会立即停止！

英文:

Inside the onDestroy() of your activity clear your handler like

  1. handler.removeCallbacksAndMessages(null);

And it will stop right away!

huangapple
  • 本文由 发表于 2020年7月26日 00:30:16
  • 转载请务必保留本文链接：https://java.coder-hub.com/63090772.html
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