FirebaseDatabase.getInstance（）崩溃的应用程序

Question

I am trying to build a tracker app using Google Maps API and Firebase. I am trying to use the getValue() method in onStart() to take values from Firebase and use them as latitude and longitude to display location. My code:

MapsActivity.java

private FirebaseDatabase firebaseDatabase=FirebaseDatabase.getInstance();
private DatabaseReference mRootReference =firebaseDatabase.getReference();
private DatabaseReference mChildReference=mRootReference.child("Raunak Trikha");
private DatabaseReference mChildReference1=mChildReference.child("id");
private DatabaseReference mChildReference2=mChildReference1.child("lat");
private DatabaseReference mChildReference3=mChildReference1.child("long");

@Override
protected void onStart(){
    super.onStart();
    mChildReference2.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            rlat=dataSnapshot.getValue(double.class);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

}`

Whenever I try to run this app in my AVD it crashes.

Answer 1

You have to call

FirebaseApp.initializeApp(getApplicationContext());

line, when your app started?

At onCreate() method of first activity or application class.

Answer 2

To simplify your code, please use the following lines:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference latRef = rootRef.child("Raunak Trikha").child("id").child("lat");
DatabaseReference longRef = rootRef.child("Raunak Trikha").child("id").child("long");
latRef.addListenerForSingleValueEvent(/* ... */);
longRef.addListenerForSingleValueEvent(/* ... */);

All this lines are needed in onCreate() method.