Foreach skips

Charles Morissette

I'm doing a foreach loop, it's looking through the controls in splitContainer1.Panel2 in one of my forms.

The purpose is to bring back all the controls from panel2, and then check if they are a groupbox. If they are, it then deletes it. My problem is it seems to only delete some of them, and leave others there.

I've added a list to check if it detects all the groupboxes, if I make the code to delete a note rather then code it will detect every groupbox. The moment I try to delete them again, it detects a different amount.

These groupboxes are dynamically created in run time, and need to be removed during the program's use.

                List BoxxCheck = new List();
                List ActualBoxes = new List();
                Parts = 0;
                foreach (Control Boxx in this.splitContainer1.Panel2.Controls)
                {
                    if (Boxx is GroupBox)
                    {
                        BoxxCheck.Add(Boxx.Name.ToString());
                        //splitContainer1.Panel2.Controls.Remove(Boxx);
                    }
                }
                lblTest.Text = string.Join(",", BoxxCheck);

Is my current code.

3 Replies

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Vulpes15y ago
Accepted answer
Just in case you (or anyone else reading this) hadn't realized why it wasn't working with foreach, the problem was that every time you removed a control from the collection the indices of all the others moved down one and so the iteration was skipping the next control.

If you're removing multiple elements from a collection, it's therefore best to always iterate backwards through the collection using an ordinary for loop so that it doesn't mess up the indexing of the elements still to be examined.
Charles Morissette15y ago
Removes them all. Thanks. I was trying to build a for to do this, but was ending up with problem. Much appreciated.
Vulpes15y ago
Try this instead:

List BoxxCheck = new List();
List ActualBoxes = new List();
Parts = 0;

for (int i = this.splitContainer1.Panel2.Controls.Count - 1; i >= 0; i--)
{
Control Boxx = this.splitContainer1.Panel2.Controls[i];
if (Boxx is GroupBox)
{
BoxxCheck.Add(Boxx.Name.ToString());
splitContainer1.Panel2.Controls.RemoveAt(i);
}
}

lblTest.Text = string.Join(",", BoxxCheck);