Question

I have 2 methods I tried to iterate through all my textboxes in an asp.net page. The first is working, but the second one is not returning anything. Could someone please explain to me why the second one is not working?

This works ok:

List<string> list = new List<string>();

    foreach (Control c in Page.Controls)
    {
        foreach (Control childc in c.Controls)
        {
            if (childc is TextBox)
            {
                list.Add(((TextBox)childc).Text);
            }
        }
    }

and the “not working” code:

List<string> list = new List<string>();

    foreach (Control control in Controls)
    {
        TextBox textBox = control as TextBox;
        if (textBox != null)
        {
            list.Add(textBox.Text);
        }
    }

Answer 1

Your first example is doing one level of recursion, so you’re getting TextBoxes that are more than one control deep in the control tree. The second example only gets top-level TextBoxes (which you likely have few or none).

The key here is that the Controls collection is not every control on the page – rather, it is only the immediate child controls of the current control (and a Page is a type of Control). Those controls may in turn have child controls of their own. To learn more about this, read about the ASP.NET Control Tree here and about NamingContainers here. To truly get every TextBox anywhere on the page, you need a recursive method, like this:

public static IEnumerable<T> FindControls<T>(this Control control, bool recurse) where T : Control
{
    List<T> found = new List<T>();
    Action<Control> search = null;
    search = ctrl =>
        {
            foreach (Control child in ctrl.Controls)
            {
                if (typeof(T).IsAssignableFrom(child.GetType()))
                {
                    found.Add((T)child);
                }
                if (recurse)
                {
                    search(child);
                }
            }
        };
    search(control);
    return found;
}

Which is used as an extension method, like so:

var allTextBoxes = this.Page.FindControls<TextBox>(true);