add button listener via for loop

Question

I'm trying to add functionality to my buttons via for loop, because I don't want to assign them in inspector.

Here is what I'm trying to do:

 for (int i = 0; i < players.Length; i++)
         {
           playersSpellers[i].spellOne_txt = spellOne_txts[i].GetComponent<Text>();
           spellOnePlus_btns[i].GetComponent<Button>().onClick.AddListener(() => playersSpellers[i].AddRemoveSpell(0, adjustSpellCount));
         }

And here is what I had to do in order to have it working in Unity

 for (int i = 0; i < players.Length; i++)
     {
       playersSpellers[i].spellOne_txt = spellOne_txts[i].GetComponent<Text>();
     }
 
     spellOnePlus_btns[0].GetComponent<Button>().onClick.AddListener(() => playersSpellers[0].AddRemoveSpell(0, adjustSpellCount));
     spellOnePlus_btns[1].GetComponent<Button>().onClick.AddListener(() => playersSpellers[1].AddRemoveSpell(0, adjustSpellCount));
     spellOnePlus_btns[2].GetComponent<Button>().onClick.AddListener(() => playersSpellers[2].AddRemoveSpell(0, adjustSpellCount));
     spellOnePlus_btns[3].GetComponent<Button>().onClick.AddListener(() => playersSpellers[3].AddRemoveSpell(0, adjustSpellCount));
     spellOnePlus_btns[4].GetComponent<Button>().onClick.AddListener(() => playersSpellers[4].AddRemoveSpell(0, adjustSpellCount));
     spellOnePlus_btns[5].GetComponent<Button>().onClick.AddListener(() => playersSpellers[5].AddRemoveSpell(0, adjustSpellCount));

I learned that it has to do something with issues with "loop closures" that are present in .NET v3.5 and that this was fixed in .NET v4.0 (and so my adding listeners using for loop would work as shown above)

I presume we won't be seeing Unity jump to .NET 4.0 anytime soon, or am I wrong? Is there a nicer solution at the moment (a workaround) to this?

Answer 1

Best Answer

Answer by fafase · Dec 11, 2016 at 03:48 PM

 for (int i = 0; i < players.Length; i++)
  {
            var ps= playersSpellers[i];
            Text t = spellOne_txts[i].GetComponent<Text>();
            ps.spellOne_txt = t;
            var clickEvent = spellOnePlus_btns[i].GetComponent<Button>().onClick;
            clickEvent.AddListener(() => ps.AddRemoveSpell(0, adjustSpellCount));
 }

By using a local variables, you should be able to bypass the issue. At least, I do it like this and it works for me.

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arhillis · Jul 07, 2017 at 08:04 PM 0

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Thank you @fafase for providing such a simple and concise answer to a problem that I have been struggling with for months.

Answer 2

Answer by PaxForce · Dec 12, 2016 at 07:19 AM

I decided to accept fafase's answer, because the idea is good, even though fafase put into local variables members of spellOne_txts, that is not neccessary at all.

I formatted my code a bit more nicely :) so this is what I used:

 for (int i = 0; i < players.Length; i++)
     {
       playersSpellers[i].spellOne_txt = spellOne_txts[i].GetComponent<Text>();
 
       var tempPlayerSpeller = playersSpellers[i];
 
       var tempSpellOnePlusButton = spellOnePlus_btns[i].GetComponent<Button>();
       tempSpellOnePlusButton.onClick.AddListener(() => tempPlayerSpeller.AddRemoveSpell(0, adjustSpellCount));
     }

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fafase · Dec 14, 2016 at 05:34 AM 0

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Yes I just got taken away with making things local...over excitement...

add button listener via for loop

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