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

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慢半拍i
慢半拍i 2021-02-02 08:05

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

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  •  灰色年华
    2021-02-02 08:32

    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.

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