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Collection of Buttons - individual callbacks

Discussion in 'UI Toolkit' started by LuKrO2011, May 16, 2022.

  1. LuKrO2011

    LuKrO2011

    Joined:
    Mar 6, 2020
    Posts:
    3
    Hello everyone,

    I am facing a problem, where I have multiple Button references stored in an array and I would like to have an individual callback depending on the index of the button. My idea to do this was the following:

    Code (CSharp):
    1. for (int i = 0; i < buttons.Length; i++)
    2. {
    3.     buttons[i].clicked += () => OnButtonClicked(i);
    4. }
    However, when any of the buttons get clicked then, the method is called with parameter i = buttons.Length.
    Is there any solution for this?

    Thank you!
    Lukas
     
    LuKrO2011, May 16, 2022
    #1

  2. martinpa_unity

    martinpa_unity

    Unity Technologies

    Joined:
    Oct 18, 2017
    Posts:
    370
    Hi!
    This happens because you are using a lambda function that will capture the 
    i
    variable.

    To fix this, you will need to assign it to a local variable before using it in your lambda:

    Code (CSharp):
    1. for (int i = 0; i < buttons.Length; i++)
    2. {
    3.     var index = i;
    4.     buttons[index].clicked += () => OnButtonClicked(index);
    5. }
    Hope this helps!
     
    martinpa_unity, May 16, 2022
    #2

  3. LuKrO2011

    LuKrO2011

    Joined:
    Mar 6, 2020
    Posts:
    3
    Hi!

    Thank you so much :)
    Again something learned about lambdas.
     
    LuKrO2011, Jun 1, 2022
    #3

  4. LuKrO2011

    LuKrO2011

    Joined:
    Mar 6, 2020
    Posts:
    3
    Hi,

    what about, if I would like to remove this specific clicked event again? Or what if I would like to remove all clicked events? How can I do this?
     
    LuKrO2011, Jun 1, 2022
    #4

  5. martinpa_unity

    martinpa_unity

    Unity Technologies

    Joined:
    Oct 18, 2017
    Posts:
    370
    If you want to remove the callback on the button, you can add the callbacks as method group:
    Code (CSharp):
    1. void OnClick()
    2. {
    3.    // code goes here
    4. }
    5.  
    6. // To add
    7. button.clicked += OnClick;
    8.  
    9. // To Remove
    10. button.clicked -= OnClick;
    Now, this would lose the index argument.

    If you want to remove all clicked event on a button, you can do 
    button.clickable = null;
    .
     
    martinpa_unity, Jun 1, 2022
    #5