Android Firebase Database How To Retrieve All Data From Child Node

I've got an app where it retrieves a bunch of data from firebase but I cant seem to make it work. database = FirebaseDatabase.getInstance(); myRef = database.getReference().chi

Solution 1:

You're creating a reference with this:

database = FirebaseDatabase.getInstance();myRef = database.getReference().child("Sold").child("Item");

And then you add a ChildEventListener. That means that the DataSnapshot in your onChildAdded will be called with a snapshot of the DUMMY 1 node first, and then with a snapshot of the DUMMY 2 node.

You're calling dataSnapshot.getValue(String.class) in onChildAdded. But since DUMMY 1 and DUMMY 2 have multiple properties, they don't have a single string value. So that call returns null, which is probably what's causing you problems.

If you want to add the DUMMY 1, DUMMY 2 key itself to the adapter, you can call dataSnapshot.getKey(). Otherwise you can get the value of the specific child properties with dataSnapshot.child("Description").getValue(String.class).

So:

myRef.addChildEventListener(newChildEventListener() {
    @OverridepublicvoidonChildAdded(@NonNull DataSnapshot dataSnapshot, @NullableString s) {
        String key = dataSnapshot.getKey();
        String description = dataSnapshot.child("Description").getValue(String.class);
        Long quantity = dataSnapshot.child("Quantity").getValue(Long.class);
        myArrayList.add(key+": "+description+" ("+quantity+")");
        myArrayAdapter.notifyDataSetChanged();
    }

---

If you'd like to read the entire value into a class representing the item (a so-called POJO), the simplest class is:

publicclassItem{
  public String Description;
  publicLong Quantity;
}

Note that the name (including the case) of the fields must exactly match the names of the properties in your database. You can use the above class like this:

myRef.addChildEventListener(newChildEventListener() {
    @OverridepublicvoidonChildAdded(@NonNull DataSnapshot dataSnapshot, @NullableString s) {
        String key = dataSnapshot.getKey();
        Item item = dataSnapshot.getValue(Item.class);
        myArrayList.add(key+": "+item.description+" ("+item.quantity+")");
        myArrayAdapter.notifyDataSetChanged();
    }

Solution 2:

The problem is that you cannot convert the dataSnapshot you are receiving into a String.

So it would be bettor to do like this:

 myRef.addChildEventListener(newChildEventListener() {
                @OverridepublicvoidonChildAdded(@NonNull DataSnapshot dataSnapshot, @NullableString s) {
                    for (DataSnapshot dummys : dataSnapshot.getChildren()) {
                        String description = dummys.child("Description").getValue(String.class);
                        int Quantity = dummys.child("Quantity").getValue(Integer.class);
                        //Use your variables here
                    }                        
                }

Or if you want to create a object of Dummy:

publicclassDummy {

StringDescription;
IntegerQuantity;

publicDummy(String description, Integer quantity) {
    Description = description;
    Quantity = quantity;
}

publicStringgetDescription() {
    returnDescription;
}

publicvoidsetDescription(String description) {
    Description = description;
}

publicIntegergetQuantity() {
    returnQuantity;
}

publicvoidsetQuantity(Integer quantity) {
    Quantity = quantity;
}

}

myRef.addChildEventListener(newChildEventListener() {
                @OverridepublicvoidonChildAdded(@NonNull DataSnapshot dataSnapshot, @NullableString s) {

                    List<Dummy> dummyList = newArrayList<>();
                    for (DataSnapshot dummys : dataSnapshot.getChildren()) {
                        dummyList.add(dummys.getValue(Dummy.class));
                    }
                }