Android- > Service -java.lang.NullPointerException

Question

I used a service for syncing process in my android app. Now i want to add a progress bar to show that syncing process is going on. But when start the service app stops showing following error. But i don't know why it's happen,

Error,

10-23 05:27:56.390: E/AndroidRuntime(25458): FATAL EXCEPTION: Timer-0
10-23 05:27:56.390: E/AndroidRuntime(25458): Process: com.abc, PID: 25458
10-23 05:27:56.390: E/AndroidRuntime(25458): java.lang.NullPointerException
10-23 05:27:56.390: E/AndroidRuntime(25458):    at com.abc.service.SynchingService$1.run(SynchingService.java:51)
10-23 05:27:56.390: E/AndroidRuntime(25458):    at java.util.Timer$TimerImpl.run(Timer.java:284)

this is my code for service,

public class SynchingService extends Service {

private Timer t;
private static MainActivity mainActivity;
ProgressDialog dialog;

@Override
public IBinder onBind(Intent intent) {

    return null;
}

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    this.timer();
    return Service.START_STICKY;
}

private void timer() {
    t = new Timer();
    t.scheduleAtFixedRate(new TimerTask() {

        @Override
        public void run() {

            mainActivity.runOnUiThread(new Runnable() {
                public void run() {
                    dialog = ProgressDialog.show(mainActivity, getString(R.string.dialog_saving), getString(R.string.dialog_please_wait));
                }
            });
            callSync();

        }
    }, 1000, 1000 * 60 * 60);

}

/**
 * This method is used to call every table to start syncing
 * 
 * @param Nothing
 * @return No return value
 */
private void callSync() {

    DataManager datamanager = DataManager.getInstance(getApplicationContext());

    Log.d("service", "running");
    // sync contact data
    ContactSync contactSync = new ContactSync();
    contactSync.contactGroupSync();
    contactSync.contactSync();

    Log.d("service2", "running2");
    // sync horse data
    HorseSync horseSync = new HorseSync();
    horseSync.horseSyncWithServer();

    Log.d("service3", "running3");
    // sync blog data
    BlogSync blogSync = new BlogSync();
    blogSync.blogSyncWithServer();

    Log.d("service4", "running4");

    // delete news categories from local DB.
    datamanager.deleteNewsCategories(MainActivity.mainActivity);
    // delete news from local DB.
    datamanager.deleteNews(MainActivity.mainActivity);
    // delete advertisement categories from local db.
    datamanager.deleteAddCategories(MainActivity.mainActivity);
    // delete advertisements from local db.
    datamanager.deleteAdds(MainActivity.mainActivity);

    dialog.dismiss();

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

}

please help me to fix this issue.

first: DO NOT STORE UI(Activity) REFERENCES INSIDE SERVICE, second: you should use Messenger class to communication between service and activity ... — Selvin, Oct 23 '14 at 10:03

Rustam · Answer 1 · 2014-10-23T10:03:10.760

0

because in your case mainActivity is null. you didn't initialized it.

edited Oct 23 '14 at 10:03

answered Oct 23 '14 at 09:45

Rustam

6,485
1
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mainActivity.runOnUiThread will also cause a crash, and you cannot replace the activity reference by getApplicationContext() since runOnUiThread is not a method of Context... – 2Dee Oct 23 '14 at 09:54
it would be ok if they will create a `public satatic Acitivty mainActivity` in `MainActivity` and initialize there. and here they can access. – Rustam Oct 23 '14 at 10:00

score 0 · Answer 2 · edited May 23 '17 at 10:26

0

You forgot to initialize your mainActivity variable, so this line will cause a crash :

mainActivity.runOnUiThread

It's generally not a good idea to show a Dialog from a Service, read this question and its accepted answer for details. You can look at this from a UX point of view : if you use the Service to sync data whether your app is open or not, that means you want to show a Dialog (thus blocking UI) that your app is syncing when the user might be performing a totally different task on his device, not related to your app, and I think we can agree that's bad. Or you use the Service to sync data only when your app is open, in which case you could just use an AsyncTask.

edited May 23 '17 at 10:26

Community

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1

answered Oct 23 '14 at 09:47

2Dee

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how can i initialize it?? – user3800832 Oct 23 '14 at 09:54
I edited my answer, please see the link about showing Dialogs in a Service. The bottom line is don't use a Dialog, use a Notification instead. – 2Dee Oct 23 '14 at 09:59
so how can i add service to sync data when my app is open /? – user3800832 Oct 23 '14 at 10:44
Use AsyncTask instead, and don't forget to check if the activity is still open once the talk finished executing before doing to update the UI. – 2Dee Oct 23 '14 at 11:58

score 0 · Answer 3 · answered Oct 23 '14 at 09:54

0

I think you should add new class to your project for getting context

So you can do it like :

Add new class and extend it from Application

public class MyApplication extends Application{

    private static Context context;

    public void onCreate(){
        super.onCreate();
        MyApplication.context = getApplicationContext();
    }

    public static Context getAppContext() {
        return MyApplication.context;
    }
}

and Declare it at manifest:

<application android:name="com.xyz.MyApplication">
</application>

Finally you can use that class when will you need context :)

answered Oct 23 '14 at 09:54

gokhan

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This will not fix the issue of the crash caused by mainActivity.runOnUiThread, you cannot call runOnUiThread on Context. – 2Dee Oct 23 '14 at 09:56
Ok, Yes @2Dee you right,Another Solution is using Messenger for communication with ui thread,Because service is viewless – gokhan Oct 23 '14 at 10:02
[link](http://stackoverflow.com/questions/4300291/example-communication-between-activity-and-service-using-messaging) will provide good example – gokhan Oct 23 '14 at 10:06

Android- > Service -java.lang.NullPointerException

3 Answers3