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

Question

Hi there!

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

Add the OnItemSelectedListener for each spinner after you have set any previous value in onResume.

Answer 2

Okay, I got it working the way I want to now.

The thing to understand here (and I did not when I was writing that question...) is that everything in Android runs in one thread - the UI thread.

Meaning: even though you set Spinner's values here and there: they are only updated (visually) and their listeners are only called after all methods you're currently in (like onCreate, onResume or whatever) are finished.

This allows the following:

• keep the selected positions in field variables. (like currentPos1, currentPos2)
• the listeners onItemSelectedListener() call a method like refreshMyResult() or whatever.
• when setting positions programmatically, set the spinners and call your own refresh method manually right after that.

The refreshMyResult() method looks like this:

int newPos1 = mySpinner1.getSelectedItemPosition();
int newPos2 = mySpinner2.getSelectedItemPosition();
// only do something if update is not done yet
if (newPos1 != currentPos1 || newPos2 != currentPos2) {
    currentPos1 = newPos1;
    currentPos2 = newPos2;

    // do whatever has to be done to update things!

}

Because the listeners will be called later - and by then, the remembered position in currentPos is already updated - nothing will happen and no unnecessary update of anything else will take place. When a user selects a new value in one of the spinners, well - the update will be performed accordingly!

That's it! :-)

Ahh - one more thing: the answer to my question is: No. The listeners cannot be disabled (easily) and will be called whenever a value is changed.