Toast from JobIntentService - android-handler

Question

I am a beginner.
I want Toast from jobintentservice (onHandleWork) but crash my app.
logcat error is : " can't toast on a thread that has not called looper.prepare()"
i want learn work with handler in jobintentservice
please help me.
public class NotificationService extends JobIntentService {
public static final String TAG = NotificationService.class.getSimpleName();
Handler handler;
public static void enqueuWork(Context context,Intent intent){
enqueueWork(context,NotificationService.class,20,intent);
}
public void onCreate() {
super.onCreate();
Toast.makeText(this, "Start background Service", Toast.LENGTH_SHORT).show();
}
#Override
public int onStartCommand(#Nullable Intent intent, int flags, int startId) {
handler = new Handler();
return super.onStartCommand(intent, flags, startId);
}
#Override
protected void onHandleWork(#NonNull Intent intent) {
handler.post(new Runnable() {
#Override
public void run()
Toast.makeText(NotificationService.this, "onhandlework", Toast.LENGTH_SHORT).show();
}
});

Answer 1

you probebly figured it out by now, but for future readers, the error "can't toast on a thread that has not called looper.prepare()" simply means you must call ui related from ui thread.
activity.runOnUiThread(new Runnable() {
#Override
public void run() {
showToast(activity);
}});
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