ValueEventListener not Working as expected

Question

I am trying to display the data stored in Firebase, in AutoCompleteTextView's Dropdown. For this purpose, I am using the ValueEventListener. According to the documentation of ValueEventListener,

You can use the onDataChange() method to read a static snapshot of the contents at a given path, as they existed at the time of the event. This method is triggered once when the listener is attached and again every time the data, including children, changes.

Unfortunately, in my case onDataChange() is triggered only when data the is changed(that is, when new data is added). This means the AutoCompleteTextView doesn't display the dropdown without any change to the data in Firebase. What I want, is for the onDataChange() to trigger for the first time when the Listener is called and every time the data changes. I would like to know where I am going wrong. The following code appears inside onCreateView of Fragment

daTags.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            //Basically, this says "For each DataSnapshot *Data* in dataSnapshot, do what's inside the method.
            for (DataSnapshot tagNameSnapshot : dataSnapshot.getChildren()) {
                //Get the suggestion by childing the key of the string you want to get.
                String ValueTagName = tagNameSnapshot.child(getResources().getString(R.string.Child_AppData_Tags_TagName)).getValue(String.class);
                //Add ValueTagName (Value pulled from Firebase for the above Key) to TagList
                //Is better to use a List, because you don't know the size of the iterator returned by dataSnapshot.getChildren() to initialize the array
                tagList.add(ValueTagName);

                //Initialize AutoCompleteTextView and define Adapter
                ArrayAdapter<String> adapterAutoComplete = new ArrayAdapter<>(getActivity(), android.R.layout.simple_list_item_1, tagList);
                actv_tagName.setAdapter(adapterAutoComplete);

                //Get TagsCount using dataSnapshot and display TagsCount in TextView
                TagsCount = dataSnapshot.getChildrenCount() + "";
                tv_tagsCount.setText(TagsCount);
            }
        });

Thanks

The onDataChange() method does indeed run once for the initial data and then again with any changes as described. I'd guess the problem is to do with the AutoCompleteTextView and Adapter though I don't have time to test it out. Try putting a Log message or something in onDataChange to confirm whether the onDataChange is running or not. — Lewis McGeary
onDataChange(){} isn't providing the initial data. However, after changing the existing data(adding a new data) in the remote database, the onDataChange(){} is working as expected (as mentioned in the question above). I would like to know what is causing the onDataChange(){} to not return the initial data. — user3314337
How have you verified onDataChange is not being triggered the first time? — Lewis McGeary
I didn't use the Log for verification. For the AutoCompleteTextView, I have the threshold set to 2 letters. For initial data, the AutoCompleteTextView doesn't display a dropdown. Also, the TagCount displays 0 for the initial data. But after adding a new data to the remote database, the AutoCompleteTextView displays a drop-down if it finds a match. Likewise, the TagCount returns the number of Tags stored in the remote database. — user3314337

user3314337 user3314337 · Accepted Answer · 2017-05-19T02:33:55

I think I understood the problem. To make it work, I will have to move the following lines of code outside the For loop

ArrayAdapter<String> adapterAutoComplete = new ArrayAdapter<>(getActivity(), android.R.layout.simple_list_item_1, tagList);
actv_tagName.setAdapter(adapterAutoComplete);

When inside the For loop, the adapter gets updated for every loop. Placing the above code outside For loop, overcomes the issue.

ValueEventListener not Working as expected

1 Answers