button.onClick.AddListener in for loop

Question

I need to add button with onclick event but I cant

 for (int i = 0; i < 10; i++)
 {
 var obj = new GameObject();
 obj.AddComponent<Button>();
 obj.GetComponent<Button>().onClick.AddListener(() => somefunc(i));
 }

problem is after Start() ends, i is setting to null and when I click on button it raises ArgumentOutOfRangeException. How can I solve this problem?

Note: All code :

     void Start () {
         player = GlobalVariables.player;
 
         for (int i = 0; i < player.items.Count; i++)
         {
             var obj = new GameObject();
             obj.AddComponent<Image>();
             Image image = obj.GetComponent<Image>();
             image.sprite = Resources.Load <Sprite>(player.items[i].slug.ToString());
 
             var wear = new GameObject();
             wear.AddComponent<RectTransform>();
             wear.AddComponent<Button>();
             wear.AddComponent<Image>();
             wear.GetComponent<Image>().sprite = Resources.Load<Sprite>("UISprite");
             wear.GetComponent<RectTransform>().transform.localScale = new Vector3(0.1f, 0.1f, wear.GetComponent<RectTransform>().transform.localScale.z);
             wear.GetComponent<Button>().onClick.AddListener(() => player.wearItem(player.items[i]));
 
             wear.transform.SetParent(obj.transform);
             obj.transform.SetParent(inventory);
 
         }
     }

Answer 1

Answer by Kaze47 · Aug 10, 2017 at 09:24 AM

I don't know why, but i have the same problem

 obj.GetComponent<Button>().onClick.AddListener(() => somefunc(i));

try

 int x = i;
 obj.GetComponent<Button>().onClick.AddListener(() => somefunc(x));

25 Show 3 · Share

jgallardoEgoGames · Aug 23, 2018 at 08:47 AM 0

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Your "try" works perfect! Looks like it's a sort of buf from Unity who lose the scope of loop variable, it's crazy because x is a copy of i but works.

Hellium jgallardoEgoGames · Aug 23, 2018 at 09:04 AM 2

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It's not a bug of Unity. It's called the closure problem, and it's a known behaviour in almost all the languages providing lambda expressions....

https://stackoverflow.com/questions/271440/captured-variable-in-a-loop-in-c-sharp

junedmmn Hellium · Dec 12, 2018 at 01:58 PM 0

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Thanks for the link.

Answer 2

Answer by junedmmn · Dec 12, 2018 at 01:56 PM

It is due to the closures simply use a copy variable, and it's done.

  for (int i = 0; i < 10; i++)
  {
     int copy = i;
     var obj = new GameObject();
     obj.AddComponent<Button>();
     obj.GetComponent<Button>().onClick.AddListener(() => somefunc(copy));
  }

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button.onClick.AddListener in for loop

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