Question

I’ve an application that has a widget already and have a service which updates that widget in every 5 seconds.

Here is my AppWidgetProvider:

public class MyWidget extends AppWidgetProvider {

    PendingIntent service = null;
    AlarmManager alarmManager;

    @Override
    public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {

        alarmManager = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
        final Intent i = new Intent(context, MyService.class);

        if(service == null) {
            service = PendingIntent.getService(context, 0, i, PendingIntent.FLAG_CANCEL_CURRENT);
        }

        alarmManager.setRepeating(AlarmManager.RTC, SystemClock.elapsedRealtime(), 1000*5, service);
    }

    @Override
    public void onDisabled(Context context) {
        Log.d("LogTag", "onDisabled");
        alarmManager.cancel(service);
        service.cancel();
    }
}

And my Service:

public class MyService extends Service {

    int b = 5;

    @Override
    public void onCreate() { super.onCreate(); }

    public int onStartCommand(Intent intent, int flags, int startId) {
        this.buildUpdate();
        return 0;
    }   

    private void buildUpdate() {
        Log.d("AAA", "Update is coming");

        RemoteViews rmViews = new RemoteViews(getPackageName(), R.layout.widget_layout);

        rmViews.setTextViewText(R.id.hello, "Iterator: " + Integer.toString(b));

        ComponentName thisWidget = new ComponentName(this, MyWidget.class);

        AppWidgetManager manager = AppWidgetManager.getInstance(this);

        manager.updateAppWidget(thisWidget, rmViews);

        b++;
    }

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

}

Service and other things are fine. But still I’ve couple questions about all these stuff:

1. What’s for SystemClock.elapsedRealtime() which is a parameter in setRepeating method? Does it point when to start?

2. When I try to delete widget, I got some errors (on below) and unfortunately AlarmManager still works not cancel. What am I missing?

3. I need to do some network operations before widget has been initialized (or called). Widget should has some data from server. Should I use AsyncTask or what?

When I try to delete widget, getting:

03-04 23:39:51.428: E/AndroidRuntime(5646): Uncaught handler: thread main exiting due to uncaught exception
03-04 23:39:51.438: E/AndroidRuntime(5646): java.lang.RuntimeException: Unable to start receiver com.example.widget.MyWidget: java.lang.NullPointerException
03-04 23:39:51.438: E/AndroidRuntime(5646):     at android.app.ActivityThread.handleReceiver(ActivityThread.java:2646)
03-04 23:39:51.438: E/AndroidRuntime(5646):     at android.app.ActivityThread.access$3100(ActivityThread.java:119)
03-04 23:39:51.438: E/AndroidRuntime(5646):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1913)
03-04 23:39:51.438: E/AndroidRuntime(5646):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-04 23:39:51.438: E/AndroidRuntime(5646):     at android.os.Looper.loop(Looper.java:123)
03-04 23:39:51.438: E/AndroidRuntime(5646):     at android.app.ActivityThread.main(ActivityThread.java:4363)
03-04 23:39:51.438: E/AndroidRuntime(5646):     at java.lang.reflect.Method.invokeNative(Native Method)
03-04 23:39:51.438: E/AndroidRuntime(5646):     at java.lang.reflect.Method.invoke(Method.java:521)
03-04 23:39:51.438: E/AndroidRuntime(5646):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
03-04 23:39:51.438: E/AndroidRuntime(5646):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
03-04 23:39:51.438: E/AndroidRuntime(5646):     at dalvik.system.NativeStart.main(Native Method)
03-04 23:39:51.438: E/AndroidRuntime(5646): Caused by: java.lang.NullPointerException
03-04 23:39:51.438: E/AndroidRuntime(5646):     at com.example.widget.MyWidget(MyWidget.java:33)
03-04 23:39:51.438: E/AndroidRuntime(5646):     at android.appwidget.AppWidgetProvider.onReceive(AppWidgetProvider.java:76)
03-04 23:39:51.438: E/AndroidRuntime(5646):     at android.app.ActivityThread.handleReceiver(ActivityThread.java:2637)
03-04 23:39:51.438: E/AndroidRuntime(5646):     ... 10 more

Answer 1

1. SystemClock.elapsedRealTime() as you have it is currently in the triggerAtTime parameter, meaning that any number you put there is the time that you want the alarm to go off. elapsedRealtime() is counted in milliseconds since the system was booted, including deep sleep. This clock should be used when measuring time intervals that may span periods of system sleep.

2. In you onDisabled method, you need to recreate the entire PendingIntent. My guess is it is null there because it doesn’t actually exist when you call onDisabled, but only exists in the onUpdate. So recreate the service variable PendingIntent exactly the same way as you do before and then call cancel on it as you already are.

3. AsyncTasks are good for things like that. An AsyncTask spawns a managed thread in the background and does work while the UI thread keeps going, then can update the UI thread when done. So if you have lots of heavy networking to do, an AsyncTask will handle that beautifully. The docs on AsyncTask are very useful. Find them here. There are many options for this depending on what you are doing, so you’d have to explain your issue on this third point in a little more detail to get a more tailored answer.