C#: Can I have a method return IEnumerator<T> and use it in a foreach loop?

Question

Howdy,

I need to set the height of every textbox on my form, some of which are nested within other controls. I thought I could do something like this:

private static IEnumerator<TextBox> FindTextBoxes(Control rootControl)
{
    foreach (Control control in rootControl.Controls)
    {
        if (control.Controls.Count > 0)
        {
            // Recursively search for any TextBoxes within each child control
            foreach (TextBox textBox in FindTextBoxes(control))
            {
                yield return textBox;
            }
        }

        TextBox textBox2 = control as TextBox;
        if (textBox2 != null)
        {
            yield return textBox2;
        }
    }
}

Using it like this:

foreach(TextBox textBox in FindTextBoxes(this))
{
    textBox.Height = height;
}

But of course the compiler spits its dummy, because foreach expects an IEnumerable rather than an IEnumerator.

Is there a way to do this without having to create a separate class with a GetEnumerator() method?

Am I mad?

Anthony

Answer 1

As the compiler is telling you, you need to change your return type to IEnumerable. That is how the yield return syntax works.

Answer 2

                    // Generic function that gets all child controls of a certain type, 
// returned in a List collection
private static List<T> GetChildTextBoxes<T>(Control ctrl) where T : Control {
  List<T> tbs = new List<T>();
  foreach (Control c in ctrl.Controls) {
    // If c is of type T, add it to the collection
    if (c is T) { 
      tbs.Add((T)c);
    }
  }
  return tbs;
}

private static void SetChildTextBoxesHeight(Control ctrl, int height) {
  foreach (TextBox t in GetChildTextBoxes<TextBox>(ctrl)) {
    t.Height = height;
  }
}

                  

Answer 3

I can't believe it was that simple, thanks.

Answer 4

If you return IEnumerator, it will be a different enumerator object each time call that method (acting as though you reset the enumerator on each iteration). If you return IEnumerable then a foreach can enumerate based on the method with the yield statement.

Answer 5

Just to clarify

private static IEnumerator<TextBox> FindTextBoxes(Control rootControl)

Changes to

private static IEnumerable<TextBox> FindTextBoxes(Control rootControl)

That should be all :-)