C＃一次删除多个按钮

Question

I'm using C# in Microsoft Visual Studio 2012. I have a program where I create a set of buttons on the fly, all are assigned the same event handler. (Fancy way for the user to choose an option.) Once this option is chosen I need to destroy all these buttons. I have been using the following code:

 foreach (Control c in this.Controls)
 {
     if (c.GetType() == typeof(Button))
     {
         c.Click -= new EventHandler(TeamChoiceButton_Click);
         this.Controls.Remove(c);
         c.Dispose();
    }
}

The problem is it is deleting every other button. I'm assuming since I'm deleting them inside the foreach, its adjusting the index so its making it skip every other one. What is the proper way to do this? Any help would be appreciated, especially if I'm misunderstanding why its skipping every other button.

Answer 1

Add a value to the Tag property of the buttons in order to mark them for a later deletion.

var btn = new Button();
btn.Tag = new object();
btn.Text = "xy";
...
this.Control.Add(btn);

Then you can remove them with:

var myButtons = this.Controls
    .OfType<Button>()
    .Where(b => b.Tag != null)
    .ToList(); //Because you cannot modify the collection being iterated with for each.
foreach (Button b in myButtons) {
    b.Click -= new EventHandler(TeamChoiceButton_Click);
    this.Controls.Remove(b);
    b.Dispose();
}

LINQ-to-object queries are executed in a lazy way. This means that the query is evaluated as the foreach-loop is going on, if we don't add a .ToList() to the query. Deleting controls from the Controls collection while the Controls collection is enumerated would throw an exception. .ToList() forces a premature evaluation of the query, thus eliminating the problem.

Answer 2

You can iterate over the list backwards and remove the items that way:

for (int i = this.Controls.Count - 1; i >= 0; i--)
{
    Control c = this.Controls[i];
    if (c.GetType() == typeof (Button))
    {
        c.Click -= new EventHandler(TeamChoiceButton_Click);
        this.Controls.RemoveAt(i);
        c.Dispose();
    }
}

Answer 3

you can put all the button you create on the fly into a List<Button> when you create it then use :

foreach (Button b in myButtonList)
{
    this.Controls.Remove(b);
}
myButtonList.Clear();