Satish Lodhi Satish Lodhi - 1 month ago 3
Android Question

Android how to remove value from firebase database?

this is my first project in firebase. I am trying to remove value from firebase but when ever i am trying to remove value from firebase, my application crashes. I am not getting how do i solve this error

Service.class

public class NotiListener extends Service {

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

//When the service is started
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
//Opening sharedpreferences
SharedPreferences sharedPreferences = getSharedPreferences(Constant.SHARED_PREF, MODE_PRIVATE);

//Getting the firebase id from sharedpreferences
String id = sharedPreferences.getString(Constant.UNIQUE_ID, null);

//Creating a firebase object
Firebase firebase = new Firebase(Constant.FIREBASE_APP + id);

//Adding a valueevent listener to firebase
//this will help us to track the value changes on firebase
firebase.addValueEventListener(new ValueEventListener() {

//This method is called whenever we change the value in firebase
@Override
public void onDataChange(DataSnapshot snapshot) {
if(snapshot.child("msg") != null){
String msg = snapshot.child("msg").getValue().toString();


if (msg.equals("none"))
return;


showNotification(msg);
} else{
Log.e("Value-->","Null");
}

}

@Override
public void onCancelled(FirebaseError firebaseError) {
Log.e("The read failed: ", firebaseError.getMessage());
}
});

return START_STICKY;
}

@Override
public void onDestroy() {
Toast.makeText(this, "MyService Stopped", Toast.LENGTH_LONG).show();
}

private void showNotification(String msg){
//Creating a notification
NotificationCompat.Builder builder = new NotificationCompat.Builder(this);
builder.setSmallIcon(R.mipmap.ic_launcher);
Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("https://www.facebook.com"));
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent, 0);
builder.setContentIntent(pendingIntent);
builder.setLargeIcon(BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher));
builder.setContentTitle("Firebase Push Notification");
builder.setContentText(msg);
NotificationManager notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
notificationManager.notify(1, builder.build());
}
}


Code for removing value is :

Firebase firebase=new Firebase(Constant.FIREBASE_APP+id);
firebase.orderByChild(id).equalTo(id).addListenerForSingleValueEvent(
new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
dataSnapshot.getRef().removeValue();

}

@Override
public void onCancelled(FirebaseError firebaseError) {

}
});


Log:

10-21 17:46:17.384 30986-30986/com.example.pitech09.bizfriend E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.pitech09.bizfriend, PID: 30986
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
at com.example.pitech09.bizfriend.NotiListener$1.onDataChange(NotiListener.java:52)
at com.firebase.client.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:56)
at com.firebase.client.core.view.DataEvent.fire(DataEvent.java:45)
at com.firebase.client.core.view.EventRaiser$1.run(EventRaiser.java:38)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5343)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:905)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:700)

Answer

dataSnapshot.getRef().setValue(null); isn't the correct way of deleting your Firebase Object. You're not allowed to save a null value to your database. To remove it, you use:

dataSnapshot.getRef().removeValue();

You should also check if the value isn't null, since you will delete that object.

if(snapshot.child("msg").getValue() != null){
   String msg = snapshot.child("msg").getValue().toString();
   return;
}