How can I dynamically clear all controls in a user control?

Question

Is it possible to dynamically (and generically) clear the state of all of a user control's child controls? (e.g., all of its TextBoxes, DropDrownLists, RadioButtons, DataGrids, Repeaters, etc -- basically anything that has ViewState)

I'm trying to avoid doing something like this:

foreach (Control c in myUserControl.Controls)
{
    if (c is TextBox)
    {
        TextBox tb = (TextBox)c;
        tb.Text = "";
    }
    else if (c is DropDownList)
    {
        DropDownList ddl = (DropDownList)c;
        ddl.SelectedIndex = -1;
    }
    else if (c is DataGrid)
    {
        DataGrid dg = (DataGrid)c;
        dg.Controls.Clear();
    }

    // etc.

}

I'm looking for something like this:

foreach (Control c in myUserControl.Controls)
    c.Clear();

...but obviously that doesn't exist. Is there any easy way to accomplish this dynamically/generically?

Answer 1

You can do

foreach (Control c in myUserControl.Controls) {
    myUserControl.Controls.Remove(c);
}

Because Controls is just a list, you can call Remove() on it, passing it what you want to remove.

EDIT: Oh I'm sorry, I didn't read it correctly. I don't know of a way to do this, maybe someone here who is good with Reflection could make it where you could do like

foreach (Control c in myUserControl.Controls) {
    c = new c.Type.GetConstructor().Invoke();
}

or something, to turn it into a freshly made component.

Answer 2

I haven't tested it, but clearing viewstate for the usercontrol may work. You could expose a custom method on the user control as well:

usercontrol:

public void Clear()
{
    this.ViewState.Clear();
}

page:

myUserControlInstance.Clear();

Now again I haven't tested. It's possible this will only clear the StateBag for the UserControl container, and not its nested/child controls.. if the above doesn't work you could try using recursion to walk down the control tree to clear viewstate for all children:

usercontrol:

public void Clear()
{
    ClearViewState(this.Controls);
}

private void ClearViewState(ControlCollection cc)
{
    foreach(Control c in cc)
    {
        if(c.HasControls())
        {
            //clear the child controls first
            ClearViewState(c.Controls);
        }        

        //then clear the control itself
        c.ViewState.Clear();
    }
}

page:

myUserControlInstance.Clear();

Just an idea. I haven't tested it but I think in theory it could work. One implication would be to call Clear at the correct point in the page/controls lifecycle, otherwise it may not work.

Hope this helps!

Answer 3

Why not do as you suggest:

foreach (Control c in myUserControl.Controls)
    c.Clear();

And then implement Clear:

public static class UserController
{
    public static void Clear( this Control c )
    {
        c.Controls.Clear();
    }

    public static void Clear( this TextBox c )
    {
        c.Text = String.Empty;
    }
}

That should do it.

Answer 4

myUserControl.Controls.ToList().ForEach(c => myUserControl.Controls.Remove(c));

However, be careful, because you modify the iterating list. This could lead to some strange behaviour.

Answer 5

Setting EnableViewState="false" on the individual controls might save you the work, if it doesn't cause other problems for you in this instance.

Answer 6

I was going to suggest a solution similar to Task's except (as sixlettervariables points out) we need to implement it as 1 extension method and essentailly switch on the precise type of the control passed in (i.e. copy your logic that you posted in your question).

public static class ControlExtensions
{
    public static void Clear( this Control c )
    {
        if(c == null) {
            throw new ArgumentNullException("c");
        }
        if (c is TextBox)
        {
            TextBox tb = (TextBox)c;
            tb.Text = "";
        }
        else if (c is DropDownList)
        {
            DropDownList ddl = (DropDownList)c;
            ddl.SelectedIndex = -1;
        }
        else if (c is DataGrid)
        {
            DataGrid dg = (DataGrid)c;
            dg.Controls.Clear();
        }
        // etc....
    }
}

It is not particularly elegent looking method but your code in your page/control is now the more succinct

foreach (Control c in myUserControl.Controls) {
    c.Clear();
}

and you can of course now call control.Clear() anywhere else in you code.

Answer 7

What about the Control.ClearChildViewState method?

MSDN states

Deletes the view-state information for all the server control's child controls.

I have never used this though. So I am unsure if it will help you. Sounds good though, I think :)