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Yield not working with onClick.AddListener.

Discussion in 'UGUI & TextMesh Pro' started by Diablo404, Aug 28, 2014.

  1. Diablo404

    Diablo404

    Joined:
    Mar 15, 2013
    Posts:
    136
    Here is a strange behaviour that I found:

    Code (JavaScript):
    1. function Start()
    2. {
    3.     button.GetComponent(UI.Button).onClick.AddListener( BtnFunction );
    4. }
    5.  
    6. function BtnFunction()
    7. {
    8.     print("test 1");
    9.     yield WaitForSeconds(1);
    10.     print("test 2");
    11. }

    Neither "test 1" nor "test 2" will appear on the console, the code seems not to be executed. But, as a workaround, this would work:

    Code (JavaScript):
    1. function Start()
    2. {
    3.     button.GetComponent(UI.Button).onClick.AddListener( Temp );
    4. }
    5.  
    6. function Temp()
    7. {
    8.     BtnFunction();
    9. }
    10.  
    11. function BtnFunction()
    12. {
    13.     print("test 1");
    14.     yield WaitForSeconds(1);
    15.     print("test 2");
    16. }

    Due to the fact that I don't have a good knowledge of how closure or event or callback should work, I don't know if it is totally normal or not. But if it is, it would be good to maybe at least throw a Warning to tell that yield are not working inside this function? Because if it is the right behaviour, I'm afraid this question/answer will pop a lot in the future.
     
    Diablo404, Aug 28, 2014
    #1

  2. superpig

    superpig

    Drink more water! Unity Technologies

    Joined:
    Jan 16, 2011
    Posts:
    4,614
    My guess is that it's because BtnFunction is a coroutine, but under the hood none of the button code is calling StartCoroutine to start it so it doesn't run properly. When you call Temp instead, Temp's call to BtnFunction generates a StartCoroutine call (as per The Magic Of UnityScript) which is why it works.

    Unfortunately I think it's going to be impossible for addListener to detect when the thing you're adding is a coroutine.
     
    superpig, Aug 28, 2014
    #2

  3. Senshi

    Senshi

    Joined:
    Oct 3, 2010
    Posts:
    557
    I don't know if UnityScript supports the delegate{} construct, but if it does you might be able to wrap it like that.

    Code (csharp):
    1. button.GetComponent(UI.Button).onClick.AddListener( delegate{ StartCoroutine( BtnFunction() ); } );
     
    Senshi, Aug 28, 2014
    #3

  4. illustir

    illustir

    Joined:
    Dec 12, 2014
    Posts:
    24
    But what if you need to yield within a delegate? Unity won't let me.
     
    illustir, Sep 22, 2015
    #4

  5. ThieLz

    ThieLz

    Joined:
    Jan 4, 2013
    Posts:
    2
    Still no solution for this problem? I have the same condition, I use delegate and need to yield waitForSeconds, but yield never return.
     
    ThieLz, Nov 4, 2015
    #5

  6. superpig

    superpig

    Drink more water! Unity Technologies

    Joined:
    Jan 16, 2011
    Posts:
    4,614
    The solution is the same as if you need to yield inside of Update: You put your yielding code in a separate function, and in your delegate you only call StartCoroutine.
     
    superpig, Nov 4, 2015
    #6