Android Spinner's onItemSelected executed twice when going back to Fragment

Question

I created a spinner for my Fragment that populates it with data retrieved from an HTTP callout. When the Fragment is first created, I populate the spinner with its selection choices, set its setOnItemSelectedListener and set its initial selection in onCreateView().

    stateSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {

        public void onItemSelected(AdapterView<?> parent, View view, int position, long id)
        {


            if (spinnerPosition != position)
            {
                spinnerPosition = position;
                TextView stateSelected = (TextView) view;
                String stateSelectedStr = stateSelected.getText().toString();


                LinearLayout ballotsDisplay = (LinearLayout) getActivity().findViewById(R.id.ballotsDisplay);
                ballotsDisplay.removeAllViews();

                Map<String, String> calloutParams = new HashMap<String, String>();
                calloutParams.put("state", stateSelectedStr);

                // Create and execute AsyncTask to retrieve ballots
                new RetrieveBallots().execute(calloutParams);
            }
        }

        public void onNothingSelected(AdapterView<?> parent) {
            return;
        }
    });

    // Set default selection for spinner
    int defaultState = adapter.getPosition(userState);

    if (defaultState == -1)
    {
        defaultState = 0;
    }

    stateSpinner.setSelection(defaultState);

When the Fragment is created, everything works well, the spinner position is set to its default and the spinner item is selected once as shown in the log below:

5009-5009/com.project.test D/TEST﹕ onCreateView called
5009-5009/com.project.test D/TEST﹕ stateSpinner.setSelection
5009-5009/com.project.test D/TEST﹕ onActivityCreated called
5009-5009/com.project.test D/TEST﹕ onResume called
5009-5009/com.project.test D/TEST﹕ spinner item selected

The problem occurs when I navigate away from the Fragment to another fragment (I store the fragment onto backstack). When I click back to go back to my original Fragment, the spinner seems to have its item selected twice:

5009-5009/com.project.test D/TEST﹕ onCreateView called
5009-5009/com.project.test D/TEST﹕ stateSpinner.setSelection
5009-5009/com.project.test D/TEST﹕ onActivityCreated called
5009-5009/com.project.test D/TEST﹕ onResume called
5009-5009/com.project.test D/TEST﹕ spinner item selected
5009-5009/com.project.test D/TEST﹕ spinner item selected

So I have 2 questions:

1) Why does the spinner register 2 item selection occurrences when returning to it from the Back button.

2) Is there a fix to prevent 2 item selections from occurring? Right now the fragment is being populated with duplicate data since it retrieves the data twice.

** EDIT ** After changing to stateSpinner.setSelection(defaultState, false) , I would get a null Pointer exception at ballotsDisplay.removeAllViews(); seems like ballotsDisplay is set to null for some reason with that change

stacktrace:

05-15 07:25:48.303 6153-6153/com.poliseewriters.polisee E/AndroidRuntime﹕ FATAL EXCEPTION: main java.lang.NullPointerException at com.polisee.ballotmeasures.BallotMeasuresFragment$1.onItemSelected(BallotMeasuresFragment.java:287) at android.widget.AdapterView.fireOnSelected(AdapterView.java:882) at android.widget.AdapterView.selectionChanged(AdapterView.java:865) at android.widget.AdapterView.checkSelectionChanged(AdapterView.java:1017) at android.widget.Spinner.layout(Spinner.java:363) at android.widget.AbsSpinner.setSelectionInt(AbsSpinner.java:292) at android.widget.AbsSpinner.setSelection(AbsSpinner.java:269) at com.polisee.ballotmeasures.BallotMeasuresFragment.setStateSpinner(BallotMeasuresFragment.java:314) at com.polisee.ballotmeasures.BallotMeasuresFragment.onCreateView(BallotMeasuresFragment.java:201) at android.support.v4.app.Fragment.performCreateView(Fragment.java:1786) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:953) at android.support.v4 .app.FragmentManagerImpl.moveToState(FragmentManager.java:1136) at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:739) at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1499) at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:456) at android.os.Handler.handleCallback(Handler.java:605) at android.os.Handler.dispatchMessage(Handler.java:92) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:4441) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) at dalvik.system.NativeStart.main(Native Method)

** EDIT: Updated code to prevent onItemSelected from executing twice, needed to add null check for ballotsDisplay **

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
    if (savedInstanceState != null) {
        Log.d("TEST", "bundle = " + savedInstanceState.toString());
    }

    Log.d("TEST", "onCreateView called");

    View view = (View) inflater.inflate(R.layout.fragment_ballot_measures, container, false);

    setStateSpinner(view);

    return view;
}


private void setStateSpinner(View view) {

    try {
        states = Utilities.getAllStateNames();
    }
    catch (Exception e) {
        Log.e("Error", "Error retrieving names: " + e.getMessage());
    }

    Spinner stateSpinner = (Spinner) view.findViewById(R.id.stateSpinner);

    final ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(), R.layout.ballotmeasures_state_spinner, states);
    adapter.setDropDownViewResource(R.layout.ballotmeasures_state_spinner_dropdown);

    stateSpinner.setAdapter(adapter);

    stateSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {

        // Callback method to invoke when a state has been selected
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id)
        {
            Log.d("TEST", "spinner item selected");

                TextView stateSelected = (TextView) view;
                String stateSelectedStr = stateSelected.getText().toString();

                // Remove all currently displayed views in the layout
                LinearLayout ballotsDisplay = (LinearLayout) getActivity().findViewById(R.id.ballotsDisplay);
                if (ballotsDisplay != null)
                {
                    ballotsDisplay.removeAllViews();
                }

                Map<String, String> calloutParams = new HashMap<String, String>();
                calloutParams.put("state", stateSelectedStr);

                // AsyncTask to execute data retrieval 
                new RetrieveBallots().execute(calloutParams);
            }

        public void onNothingSelected(AdapterView<?> parent) {
            return;
        }
    });

    // Set default selection for spinner
    int defaultState = adapter.getPosition(userState);

    if (defaultState == -1)
    {
        defaultState = 0;
    }

    Log.d("TEST", "stateSpinner.setSelection");
    stateSpinner.setSelection(defaultState, false);
}

Answer 1

Use stateSpinner.setSelection(defaultState, false); in place of stateSpinner.setSelection(defaultState);

Answer 2

The problem is the onItemSelected() callback gets called twice by Android Framework (maybe by design), the first time the view parameter is null , and the second time it is instantiated.

You cannot prevent 2 item selections from occurring, but you can check if the view variable is null, if not, do the rest things.

Answer 3

Add condition view!=null in ItemSelectedListener like this:

spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
                    @Override
                    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {

                        if(view!=null)
                        {//write your code
                        }
                    }

                    @Override
                    public void onNothingSelected(AdapterView<?> parent) {

                    }
                });