Retrieve String Out of Addvalueeventlistener Firebase

Retrieve String out of addValueEventListener Firebase

The data is loaded from Firebase asynchronously. By the time you run title = a, the onDataChange method hasn't been called yet. Set some breakpoints in a debugger to verify this, it's key to understanding how asynchronous loading works.

The solution is to reframe your problem from "first get the object, then do blabla with the title" to "start getting the object; once the object is available, do blabla with the title".

In code this translates to:

final DatabaseReference mPostReference = FirebaseDatabase.getInstance().getReference().child("user-daily").child(getUid()).child("2017-Year");
mPostReference.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        final ArrayList<String> labels = new ArrayList<String>();
        for (DataSnapshot data : dataSnapshot.getChildren()){
            final DailyItem dailyItem = data.getValue(DailyItem.class);
            labels.add(dailyItem.mese);

        }
        title.setText(labels.get(position));

        // Do blabla with the title
        String title = title.getText().toString();
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        Toast.makeText(view.getContext(),"database error",
                Toast.LENGTH_SHORT).show();
    }
});

Many developers new to Firebase (and other modern web APIs, as they all work this way) struggle with this problem. So I recommend you also check out their questions and answers:

• Cannot access firebaseObjectObservable outside of set
• Android Firebase get value of child without DataChange
• Value of a global variable is reset after it is initialised in ValueEventListener
• can't get values out of ondatachange method
• ArrayList not updating inside onChildAdded function
• Setting Singleton property value in Firebase Listener
• and most others in this list of search results

How to get the string values from a query inside a for loop being used for an addValueEventListener

Data from Firebase is only available inside the onDataChange method, or in code called from there. There is no workaround for this.

If you require an additional database call to load additional data, you should:

• either hold off adding the item to the list at first, and then only add it in the inner onDataChange
• or add the incomplete item to the list at first, and then update it in the inner onDataChange

So the simplest fix is to do the first, which looks something like this:

query.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        for (DataSnapshot dataSnapshot1 : dataSnapshot.getChildren()) {
            rank = "" + dataSnapshot1.child("rank").getValue();
            profilePicture = "" + dataSnapshot1.child("image").getValue();
            username = "" + dataSnapshot1.child("username").getValue();

            chatsItemArrayList.add(new ChatsItem(getProfilePicture(), title, date, speaks, description, getUsernameText(), getRankText(), upvotes, views, picture));

        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        throw databaseError.toException();
    }
});

You'll typically want to also refresh the adapter in that inner onDataChange method by calling something like adapter.notifyDataSetChanged().

Also see:

• getContactsFromFirebase() method return an empty list
• Wait Firebase async retrieve data in Android
• Only load layout when firebase calls are complete
• and many more from this list

not be able to retrieve firebase data using addValueEventListener

I think its nested too much but to answer your question, you need to remove this from your code:

  dealList.clear();

and add it outside of the addValueEventListener()

like this:

protected void onStart() {
super.onStart();
   dealList.clear();
rootRef.addValueEventListener(new ValueEventListener() {

Edit:

  @Override
 protected void onStart() {
super.onStart();
  dealList.clear();
rootRef.child(expertId).child("Cooker Deals").addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {

        for(DataSnapshot dealSnapshot : dataSnapshot.getChildren()){
         for(DataSnapshot datas : dealSnapshot.getChildren(){
             NewDeal_Database info = datas.getValue(NewDeal_Database.class);
            dealList.add(info);

        }

        DealList adapter = new DealList( New_Deal_List.this,dealList);
        lvDealList.setAdapter(adapter);
        adapter.notifydatasetchanged();
    }

Data being lost after addValueEventListener Firebase Android

The line

Log.d("after","valu" + newDay.toString());

is calling before firebase gets result from database.
All you need to do is create a method

public void printResult(){
  Log.d("after","valu" + newDay.toString());
}

Now call this method as

newDay = new ArrayList<Integer>();
        mUserDatabase.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {

newDay.addAll((ArrayList<Integer>)dataSnapshot.getValue());
                Log.d("newday", "onDataChange:"+newDay.toString());
                printResult();
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

Reason

Firebase has it's own async mechanism like volley library onDataChange function will be call when firebase gets some result from internet and execute the below code as normally in your case below code is your Log.d("after","value"+newDay.toString()); line.

Hope this will help you.

how to retrieve data from fire base and assign to a string

    DatabaseReference mDatabase = FirebaseDatabase.getInstance().getReference();

    mDatabase.child("menu").addValueEventListener(new ValueEventListener() {
     @Override
     public void onDataChange(DataSnapshot dataSnapshot) {

         //This will loop through all items. Add variables to arrays or lists as required
         for (DatasnapShot snap : dataSnapshot.getChildren())
         {
             foodname = dataSnapshot.child("name").getValue().toString();
             String prize = dataSnapshot.child("prize").getValue().toString();
         }

     }

     @Override
     public void onCancelled(DatabaseError databaseError) {
     }
 });

You can fetch each child individually like such. Or you can make use of a Model or a Hashmap to fetch all of the data and then fetch the data you would like based on the Key

Retrieving data in firebase database without calling addValueEventListener

Firebase api is asynchronous meaning that when you use AddValueEventListener to retrieve data from the database, the program will not stop and continue executing. Therefore in this log:

Log.i("Original_Quantity", ""+originalQuantity);

You will get null since it is executed before the data is fully retrieved. There are two ways to access the data either inside the onDataChange or you can do the following:

How to return DataSnapshot value as a result of a method?

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