Firebase Android count children/ badge

Question

I try to develop a simple shopping application. There will be a few product categories and I use different activity with ListView for every category. When User choose product category (say items1 ="drinks")- new screen opens and he can add "soda", "cola"... I want to add count badge on every category to show number of products per category. So, for example for "items" I need to display 5, for "items1" - 2 and for "items10/11" - display 1:

my ActivityItems1 code:

 private Firebase mRef; private String mUserId; private String itemsUrl; private TextView badge; itemsUrl = Constants.FIREBASE_URL + "/users/" + mUserId + "/items1"; // Set up LisView final ListView listView = (ListView) findViewById(R.id.listView); final ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, android.R.id.text1); listView.setAdapter(adapter); // Find badge badge =(TextView)findViewById(R.id.badgeView); // Use Firebase to populate the list. new Firebase(itemsUrl) .addChildEventListener(new ChildEventListener() { @Override public void onChildAdded(DataSnapshot dataSnapshot, String s) { adapter.add((String) dataSnapshot.child("title").getValue()); Log.e(dataSnapshot.getKey(), dataSnapshot.getChildrenCount() + ""); badge.setText(dataSnapshot.getChildrenCount() + ""); }

After running the code I received Key and number of his children: E-KJGG2driQ6HJI8R7eve: 1 E-KJGG3Ua6rmlQYn4IHF: 1

it's always 1 child for every Key because Key=Product ID and child of the Key - it's title. But I need to count Keys/ Product IDs (products in category "drinks") and not his children...

You could use a child added and child changed value instead of a value event type, this way you could simply use the dataSnapshot.getChildrenCount() — Ymmanuel
– Ymmanuel, Commented Jun 2, 2016 at 19:33
@YmmanuelFlores getChildrenCoun() only makes sense for a value event. Otherwise you simply get a count of the number of properties, which is unlikely to be what OP wants. — Frank van Puffelen
– Frank van Puffelen, Commented Jun 2, 2016 at 19:56
badgeView=null indicates that you haven't initialized badgeView and thus it will throw a NullPointerException when you call badgeView.setText(). You're likely missing a badgeView = findViewById() in your onCreate() method. — Frank van Puffelen
– Frank van Puffelen, Commented Jun 2, 2016 at 19:59
@FrankvanPuffelen ... Nope...if you set the reference at the parent of items...items1....items10...etc and use the child_added..in each event he would receive a snapshot for each event..(the key of the first event would be 'items') there he can use the getChildrenCount() that would count the children..(-kj....) and that is what OP wants — Ymmanuel
– Ymmanuel, Commented Jun 2, 2016 at 20:02
@YmmanuelFlores child_added fires at the child level, it will not fire for the parent. Try it. — Frank van Puffelen
– Frank van Puffelen, Commented Jun 2, 2016 at 20:11

Ymmanuel · Accepted Answer · 2016-06-02 20:39:37Z

With this Database you have two options:

1)Use Child Added

FirebaseDatabase database = FirebaseDatabase.getInstance(); DatabaseReference myRef = database.getReference(); //You must remember to remove the listener when you finish using it, also to keep track of changes you can use the ChildChange myRef.addChildEventListener(new ChildEventListener() {     @Override     public void onChildAdded(DataSnapshot dataSnapshot, String s) {         Log.e(dataSnapshot.getKey(),dataSnapshot.getChildrenCount() + "");     }     @Override     public void onChildChanged(DataSnapshot dataSnapshot, String s) {     }     @Override     public void onChildRemoved(DataSnapshot dataSnapshot) {     }     @Override     public void onChildMoved(DataSnapshot dataSnapshot, String s) {     }     @Override     public void onCancelled(DatabaseError databaseError) {     } });

2)Use the Value listener

FirebaseDatabase database = FirebaseDatabase.getInstance(); DatabaseReference myRef = database.getReference(); //You can use the single or the value.. depending if you want to keep track thismyRef.addListenerForSingleValueEvent(new ValueEventListener() {     @Override     public void onDataChange(DataSnapshot dataSnapshot) {         for (DataSnapshot snap: dataSnapshot.getChildren()) {             Log.e(snap.getKey(),snap.getChildrenCount() + "");         }     }     @Override     public void onCancelled(DatabaseError databaseError) {     } });

Here is the output for both cases

If you need to keep constant tracking is best to use the Child events...because otherwise each time anything changes you will receive the entire json over the network, instead of only the portion of information that was changed

If you need a snapshot only once, you better use the singleValue since this way you will receive all the information at the same time

This answer was made using the new Firebase 3....if you are still using the legacy version and you cannot migrate...the solution will still work the only thing that changes is the way you get your database reference as established here firebase.google.com/support/guides/…
I tried the 2nd approach and my code looks now like this: new Firebase(itemsUrl).addListenerForSingleValueEvent(new ValueEventListener() { @Override public void onDataChange(DataSnapshot dataSnapshot) { ... badge.setText((int) snap.getChildrenCount() + ""); and still can't see the count on badge...I feel like I do some stupid syntax mistake - but can't figure it out...
Ymmanuel, It seems like I didn't explain clear enough my situation. I have different activities for different items: one for "items", second for "items1"... ("item"&"item1"= product categories: dairy, drinks...) And when I tried to implement ChildAdded approach - I received Key and number of his children -it's always 1 child for every Key in this case because Key=Product ID and child of the Key - it's title). But I need to count Product IDs (products in category) and not his children.
In SQL it should be: Select count (Key/ProductID) from items; select count (Keys) from items1 etc. So for "items" in first activity I receive 5, for “items1” – 2. I’ll very appreciate for any help!

Rıdvan · Accepted Answer · 2016-06-02 19:38:03Z

I'm not sure about that but It can couse of parsing. Try to

badgeView.setText(nums+"");

maybe It could help.

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