Button onClick wrong parameter in Unity C# [duplicate]

Question

I have a ScrollView with a Grid Layout Group component on the Content object :

My item list is inside the Content object and each item own a Button component.

I'm trying to add the onClick programmatically to handle a lot of objects and index with a parameter like this :

        int i = 0;
        foreach(Button btn in scrollViewContent.GetComponentsInChildren<Button>()) {
            btn.onClick.AddListener(() => Load(i));
            i++;
        }

However onClick I always get the last index + 1 on all item click. Here are my logs :

Until Log 44, this is the foreach print loop and the Log "index : 45" is the result on click.

So two question :

• Why all item click return the same index ?

• How can I get index 45 whereas the i var stopped at 44 ?

as you didnt share the code with the debug log in, its hard to know but if there are 0-44 items, after the 44th item i will be 45.. — BugFinder
– BugFinder, Commented Nov 21, 2023 at 20:06

hijinxbassist · Accepted Answer · 2023-11-21 21:38:17Z

1

The issue is that the callbacks all use the same variable. This may seem odd since an int is a value type and must be copied. However, the variable is captured in the local scope, resulting in the same variable being used across all callbacks.

To solve the issue, create a new local variable inside of the foreach loop.

var i = 0;

foreach (var button in buttons)
{
    var index = i++;

    button.onClick.AddListener(() => Load(index)); 
}

answered Nov 21, 2023 at 21:38

hijinxbassist

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