Iterating over ControlCollection returns 0 results

Question

I have the following method to return a List of WebControls in my helper class:

public static List<T> GetControls<T>(ControlCollection cCol) where T : WebControl
{
    List<T> results = new List<T>();
    foreach (Control control in cCol)
    {
        if (control is T)
            results.Add((T)control);

        if (control.HasControls())
            GetControls<T>(control.Controls);
    }
    return results;
}

On my aspx page there is one UpdatePanel containing 3 asp:CheckBoxList controls. To populate my List I use the above described method, where CheckBoxPanel is the UpdatePanel containing my controls.

List<CheckBoxList> cbCol = Helper.GetControls<CheckBoxList>(CheckBoxPanel.Controls);

This line returns 0 results, which indicates, that my method GetControls<T>(ControlCollection cCol) is wrong.

Please help my find the flaw in my train of thoughts.

Answer 1

Your results is a local variable. So for every recursive call you add some controls and forget it.

It should be passed as a parameter in all the recursive calls, only then controls will be populated in same list.

Not tested, but the following code should work:

private static List<T> GetControls<T>(ControlCollection cCol, List<T> results) where T : WebControl
{
    foreach (Control control in cCol)
    {
        if (control is T)
            results.Add((T)control);
        if (control.HasControls())
            GetControls<T>(control.Controls, results);
    }

    return results;
}

public static List<T> GetControls<T>(ControlCollection cCol) where T : WebControl
{
    return GetControls(cCol, new List<T>());
}