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C # ControlCollection GetAllTextboxes Extension

How can I get only the textboxes in the ControlCollection?

I'm trying to:

public static IEnumerable<TextBox> TextBoxes(this ControlCollection controlCollection)
{
    return (IEnumerable<TextBox>)controlCollection.Cast<Control>().Where(c => c is TextBox);
}

But I got the following error: Unable to pass object of type "WhereEnumerableIterator`1 [System.Web.UI.Control]" for input "System.Collections.Generic.IEnumerable`1 [System.Web.UI.WebControls.TextBox]".

I am using Asp.Net 3.5 with C #

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4 answers


You don't really need a new extension method - there's already one for you, which will get the following:

controlCollection.OfType<TextBox>();

The OfType method returns a subset of the sequence ( IEnumerable<T>

) of the provided sequence. If the type is not convertible, it is ignored. Unlike most LINQ extension methods, it OfType

is available for sequences that are not strongly typed:



This method is one of the few standard query operator methods that can be applied to a collection that is of a non-parameterized type, such as ArrayList. This is because OfType <(Of <(TResult>)>) extends IEnumerable.

Or, if you want to wrap it in an extension method, it's of course pretty simple:

public static IEnumerable<TextBox> TextBoxes(this ControlCollection controls)
{
    return controls.OfType<TextBox>();
}
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You want OfType ():



public static IEnumerable<TextBox> TextBoxes(this ControlCollection controlCollection)
{
    return controlCollection.OfType<TextBox>();
}
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Here is a recursive extension method to get objects Control

that are omitted from the specified type, including those nested in the control hierarchy.

public static class ControlCollectionExtensions
{
    public static IEnumerable<T> OfTypeRecursive<T>(this ControlCollection controls) where T : Control
    {
        foreach (Control c in controls)
        {
            T ct = c as T;

            if (ct != null)
                yield return ct;

            foreach (T cc in OfTypeRecursive<T>(c.Controls))
                yield return cc;
        }
    }
}

(For Windows Forms, replace ASP.NET Control.ControlCollection

with ControlCollection

.)

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foreach (TextBox tBox in controls)
{

}

Example:

public static void HideControls<T>(Form pForm)
{
    foreach (T cont in pForm.Controls)
    {
        cont.Visible = false;
    }
}

HideControls<TextBox>(this);
HideControls<CheckedListBox>(this);
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