LinkLabel Click event being overwritten within loop

Question

Here's some sample code which denotes my problem. It adds 5 LinkLabels, each with a Click event handler. The text on the label is 1...5 and should display the same result when clicked, but when I click on each of the labels I get the same message for each: 5.

It's like the last handler is overwriting the handler on each of the other labels. I thought I had avoided that by creating a new EventHandler and new LinkLabel each iteration of the loop.

I added each LinkLabel to a FlowLayoutPanel.

Why am I getting this result, and how can I fix it?

List<Test> objects = new List<Test>();
for (int i = 0; i < 5; i++)
{
    objects.Add(new Test(i + 1));
}

foreach (Test t in objects)
{
    LinkLabel label = new LinkLabel();
    label.AutoSize = true;
    label.Text = t.a + "";

    label.Click += new EventHandler((sender, args) =>
    {
        MessageBox.Show(t.a + "");
    });

    flowLayoutPanel1.Controls.Add(label);
}

J0e3gan · Answer 1 · 2014-10-15T03:28:20.220

In my attempt to reproduce the problem you described with your code, the link labels 1 through 5 displayed 1 through 5 respectively when clicked just like you want.

Here is a standalone example that minimally builds upon the code you posted (just to the extent necessary to make it build and run)...and works as expected:

// FORNOW: Added Main method for PoC.
void Main()
{
    // FORNOW: Added necessary Form and FlowLayoutPanel locals.
    Form form1 = new Form();
    FlowLayoutPanel flowLayoutPanel1 = new FlowLayoutPanel();

    List<Test> objects = new List<Test>();
    for (int i = 0; i < 5; i++)
    {
        objects.Add(new Test(i + 1));
    }

    foreach (Test t in objects)
    {
        LinkLabel label = new LinkLabel();
        label.AutoSize = true;
        label.Text = t.a + "";

        label.Click += new EventHandler((sender, args) =>
        {
            MessageBox.Show(t.a + "");
        });

        flowLayoutPanel1.Controls.Add(label);
    }

    // FORNOW: Added necessary control wiring and display call.
    form1.Controls.Add(flowLayoutPanel1);
    form1.Show();
}

// FORNOW: Added a Test class based on the OP's code.
public class Test
{
    public int a { get; set; }

    public Test(int a)
    {
        this.a = a;
    }
}

You may have a problem in other code you are employing, but the code you shared works fine based on what you said you expect.

Hm, that's weird, I'm still getting the same problem. each of the labels when clicked sends the message "5" — kschieck, Oct 15 '14 at 03:46
Got it, for some reason it was referencing the same object. so when I created a variable like `string a = t.a + " ";` then it would contain the right values; — kschieck, Oct 15 '14 at 03:50
@kschieck, the reason would be in the state of the code before you (changed it and) "got it": you should post an answer that explains the solution once you have isolated it. You should also consider upvoting my answer if it proved useful. :} — J0e3gan, Oct 15 '14 at 04:27

LinkLabel Click event being overwritten within loop

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