How to disable onItemSelectedListener to be invoked when setting selected item by code

Question

Just wondering how you handle the following problem: a result is calculated depending on two spinners' selected items. To handle the UI things, i.e. a user picks a new item in one of the spinners, I install a listener using setOnItemSelectedListener for the spinner in my onCreate() method of the activity.

Now: that works, of course, fine. The listener's work is to trigger a new calculation of the result.

The problem: because I intercept onPause() onResume() to save/restore the last state, I got a method that sets these two spinners' selected item programmatically like in here:

startSpinner.setSelection(pStart);
destSpinner.setSelection(pDest);

These two calls invoke the listeners, too! My calculation method for the result plus the notification of a new result set is invoked twice here!

A stupid direct approach for this would be to have a boolean variable disabling whatever the listener does inside, setting it before setting the selected items and resetting it afterwards. Okay. But is there a better method??

I don't want listeners to be called by code - actions, only by user actions! :-(

How do you do it? Thanks!

Answer 1

A cleaner solution, in my opinion, to differentiate between programmatic and user-initiated changes is the following:

Create your listener for the spinner as both an OnTouchListener and OnItemSelectedListener

public class SpinnerInteractionListener implements AdapterView.OnItemSelectedListener, View.OnTouchListener {

    boolean userSelect = false;

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        userSelect = true;
        return false;
    }

    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {
        if (userSelect) { 
            // Your selection handling code here
            userSelect = false;
        }
    }

}

Add the listener to the spinner registering for both event types

SpinnerInteractionListener listener = new SpinnerInteractionListener();
mSpinnerView.setOnTouchListener(listener);
mSpinnerView.setOnItemSelectedListener(listener);

This way, any unexpected calls to your handler method due to initialization or re-initialization will be ignored.