Question

I have a foreach loop inside of an button-click event handler that I’m using to get rid of controls that all sit on the same point on the Y axis. I have a control that adds a row, and then I need users to have the option to remove a row they didn’t mean to add.

When I use the foreach loop by itself, it consistently misses two items–the same two every time. I’ve confirmed that the Y values are in fact identical. If I keep running the function, it removes all the controls on the row after three runs. However, if I nest the foreach loop, using all the same values, it works. See the code below.

This seems like a pretty sloppy way to do it, but it’s also the only solution that has worked for me. I saw a couple other posts that said to declare a second variable within the loop (i.e., Control z = c; if(z.Location....)). That didn’t make any difference in the behavior here. Can anyone explain why the foreach loop by itself isn’t working? How do I fix it without the repetitive nesting?

Working:

    internal void MinButt_Click(object sender, EventArgs e)
    {
        Scratch.tScratch.panel2.Controls.RemoveByKey("Record" + arrDynamY[0].ToString());
        foreach (Control c in Scratch.tScratch.panel2.Controls)
        {
            if (c.Location.Y == arrDynamY[1])
            {
                c.Dispose();
            }

            foreach (Control ctrl in Scratch.tScratch.panel2.Controls)
            {
                if (ctrl.Location.Y == arrDynamY[1])
                {
                    ctrl.Dispose();
                }
            }
        }
    }

Misses the same two controls every time:

    internal void MinButt_Click(object sender, EventArgs e)
    {
        Scratch.tScratch.panel2.Controls.RemoveByKey("Record" + arrDynamY[0].ToString());
        foreach (Control c in Scratch.tScratch.panel2.Controls)
        {
            if (c.Location.Y == arrDynamY[1])
            {
                c.Dispose();
            }
        }
    }

Answer 1

You should firstly obtain controls for removing and remove them afterwards like this:

var controlsToRemove = from Control c in Scratch.tScratch.panel2.Controls
                       where c.Location.Y == arrDynamY[1]
                       select c;

foreach (var c in controlsToRemove.ToArray())
{
    Scratch.tScratch.panel2.Controls.Remove(c);
    c.Dispose();
}