Android的Handler在活动被销毁后仍然持续运行一段时间。

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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:

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        SensorManager sm = (SensorManager) getSystemService(SENSOR_SERVICE);
        Sensor light = sm.getDefaultSensor(Sensor.TYPE_LIGHT);
        SensorEventListener listener;

        if (light != null) {
            final Handler handler = new Handler();
            final Runnable task = new Runnable() {
                @Override
                public void run() {
                    sm.registerListener(listener, light, SensorManager.SENSOR_DELAY_NORMAL);
                }
            };

            listener = new SensorEventListener() {
                @Override
                public void onAccuracyChanged(Sensor sensor, int accuracy) {
                    Toast.makeText(MainActivity.this, "accuracy changed!", Toast.LENGTH_SHORT).show();
                }

                @Override
                public void onSensorChanged(SensorEvent event) {
                    sm.unregisterListener(listener, light);

                    // 在此处处理接收到的传感器光线值,即event.values[0]

                    handler.postDelayed(task, 2000);
                }
            };
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        sm.unregisterListener(listener, light);
    }

    @Override
    protected void onResume() {
        super.onResume();
        sm.registerListener(listener, light, SensorManager.SENSOR_DELAY_NORMAL);
    }

    @Override
    protected void onStop() {
        super.onStop();
        sm.unregisterListener(listener, light);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        sm.unregisterListener(listener, light);
    }
}

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onStoponDestroy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:

public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
SensorManager sm = (SensorManager) getSystemService(SENSOR_SERVICE);
Sensor light = sm.getDefaultSensor(Sensor.TYPE_LIGHT);
SensorEventListener listener;
if (light != null) {
final Handler handler = new Handler();
final Runnable task = new Runnable() {
@Override
public void run() {
sm.registerListener(listener, light, SensorManager.SENSOR_DELAY_NORMAL);
}
};
listener = new SensorEventListener() {
@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {
Toast.makeText(MainActivity.this, "accuracy changed!", Toast.LENGTH_SHORT).show();
}
@Override
public void onSensorChanged(SensorEvent event) {
sm.unregisterListener(listener, light);
// Do the stuff here with the received sensor light value, which is event.values[0]
handler.postDelayed(task, 2000);
}
};
}
@Override
protected void onPause() {
super.onPause();
sm.unregisterListener(listener, light);
}
@Override
protected void onResume() {
super.onResume();
sm.registerListener(listener, light, SensorManager.SENSOR_DELAY_NORMAL);
}
@Override
protected void onStop() {
super.onStop();
sm.unregisterListener(listener, light);
}
@Override
protected void onDestroy() {
super.onDestroy();
sm.unregisterListener(listener, light);
}
}

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:

handler.removeCallbacksAndMessages(null);

这样就会立即停止!

英文:

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

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://go.coder-hub.com/63090772.html
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