//Writing data and using call-back functions documentReference.set(user).addOnCompleteListener(new OnCompleteListener<Void>() { @Override public void onComplete(@NonNull Task<Void> task) { if (task.isSuccessful()) { //Tas was successful Toast.makeText(MainActivity.this, "User Added", Toast.LENGTH_SHORT).show(); }else{ //Something went wrong Log.e(TAG, "onComplete: Error: " + task.getException().getLocalizedMessage() ); } } });