c# for-loop and Click Event Handler

Question

How do I use one individual event handler per iteration, without hard coding the functions?

for (int i = 0; i < 100; i++)
{
        //other code
        PictureBox listItem = new PictureBox();
        listItem.Click += new EventHandler((sender2, e2) => ListItemClicked(i));
        //other code     
}

private void ListItemClicked(int index)
{
    MessageBox.Show(index.ToString());
}

You already using one handler per iteration, aren't you? Can you please explain more? — Timothy Ghanem, Jul 16 '16 at 11:57
Yes, I do, but the ListItemClicked() function just shows index 100 (the last index), no matter which listItem I click. — Reese, Jul 16 '16 at 11:58

Marco · Accepted Answer · 2016-07-16T12:12:42.193

You need to copy your iterator into a local variable for the delegate to capture it correctly:

for (int i = 0; i < 100; i++)
{
        var idx = i;
        //other code
        PictureBox listItem = new PictureBox();
        listItem.Click += new EventHandler((sender2, e2) => ListItemClicked(idx));
        //other code     
}

In you original piece of code, the delegate says "return me the current value of the variable", which is 100. Not: "the value when it was created". Read up on closures to get an in depth explanation of this. I'd recommend Jon Skeets C# in depth.

In c# 5.0 this was changed for the foreach loop, not the for i; one though.

c# for-loop and Click Event Handler

1 Answers1