Android：在后台服务中打开/关闭屏幕时帮助计数

Question

For a little app that I'm working at I need to count how many times the screen turns off and on and when it does that. I created a BroadcastReceiver that runs a Service after booting that is supposed to count that.

This is my Service class:

public class MyService extends Service {

  private final IBinder mBinder = new MyBinder();
  public static boolean wasScreenOn = true;

  @Override
  public int onStartCommand(Intent intent, int flags, int startId) {
    //the next line is line 29
      if (intent.getAction().equals(Intent.ACTION_SCREEN_OFF)) {
        Log.i("Screen off", String.valueOf(System.currentTimeMillis()));
            wasScreenOn = false;
        } else if (intent.getAction().equals(Intent.ACTION_SCREEN_ON)) {
            Log.i("Screen on", String.valueOf(System.currentTimeMillis()));
            wasScreenOn = true;
        }
      return Service.START_NOT_STICKY;
  }

  @Override
  public IBinder onBind(Intent arg0) {
  //TODO for communication return IBinder implementation
        return mBinder;
  }

  public class MyBinder extends Binder {
        MyService getService() {
          return MyService.this;
        }
      }

}

The problem is that I get this error:

06-26 23:16:38.485: E/AndroidRuntime(1402): FATAL EXCEPTION: main
06-26 23:16:38.485: E/AndroidRuntime(1402): java.lang.RuntimeException: Unable to start service com.MyApp.MyService@40ce0078 with Intent { cmp=com.MyApp/.MyService (has extras) }: java.lang.NullPointerException
06-26 23:16:38.485: E/AndroidRuntime(1402):     at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2673)
06-26 23:16:38.485: E/AndroidRuntime(1402):     at android.app.ActivityThread.access$1900(ActivityThread.java:141)
06-26 23:16:38.485: E/AndroidRuntime(1402):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1331)
06-26 23:16:38.485: E/AndroidRuntime(1402):     at android.os.Handler.dispatchMessage(Handler.java:99)
06-26 23:16:38.485: E/AndroidRuntime(1402):     at android.os.Looper.loop(Looper.java:137)
06-26 23:16:38.485: E/AndroidRuntime(1402):     at android.app.ActivityThread.main(ActivityThread.java:5041)
06-26 23:16:38.485: E/AndroidRuntime(1402):     at java.lang.reflect.Method.invokeNative(Native Method)
06-26 23:16:38.485: E/AndroidRuntime(1402):     at java.lang.reflect.Method.invoke(Method.java:511)
06-26 23:16:38.485: E/AndroidRuntime(1402):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
06-26 23:16:38.485: E/AndroidRuntime(1402):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
06-26 23:16:38.485: E/AndroidRuntime(1402):     at dalvik.system.NativeStart.main(Native Method)
06-26 23:16:38.485: E/AndroidRuntime(1402): Caused by: java.lang.NullPointerException
06-26 23:16:38.485: E/AndroidRuntime(1402):     at com.MyApp.MyService.onStartCommand(MyService.java:29)
06-26 23:16:38.485: E/AndroidRuntime(1402):     at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:2656)

I imagine it is because when the Service starts there is still no Intent for Screen On/Off. But I want this Service to run in the background and wait for it.

How should I do this?

Thanks a lot!

Answer 1

Your problem is NullPointerException in onStartCommand . The intent is null .

From the documentation :

intent The Intent supplied to startService(Intent), as given. This may be null if the service is being restarted after its process has gone away, and it had previously returned anything except START_STICKY_COMPATIBILITY.

You should check for null value before you do anything with the intent .

Answer 2

I made it work after I used the code from this app

Code:

public class HardwareTriggerService extends Service {
private HardwareTriggerReceiver hardwareTriggerReceiver;
@Override
public void onCreate() {
    super.onCreate();
    Log.e(">>>>>>", "HardwareTriggerService CREATED.");
    IntentFilter filter = new IntentFilter();
    filter.addAction(Intent.ACTION_SCREEN_ON);
    filter.addAction(Intent.ACTION_SCREEN_OFF);
    hardwareTriggerReceiver = new HardwareTriggerReceiver();
    registerReceiver(hardwareTriggerReceiver, filter);
}

@Override
public void onDestroy() {
    super.onDestroy();
    Log.e(">>>>>>", "HardwareTriggerService DESTROYED.");
    IntentFilter filter = new IntentFilter();
    filter.addAction(Intent.ACTION_SCREEN_ON);
    filter.addAction(Intent.ACTION_SCREEN_OFF);

    unregisterReceiver(hardwareTriggerReceiver);
}

@Override
public IBinder onBind(Intent intent) {
    return null;
}
}