How to clear list boxes in a content page. The content page is inside of a content place holder control

with the id="ContentPalceHolder1"

C#

 ' ---use this code for a content page webform

For Each ctrl In Me.Master.FindControl("ContentPlaceHolder1").Controls
     If ctrl.GetType() Is GetType(TextBox) Then
            CType(ctrl, TextBox).Text = ""
     End If
Next

C#

 //---for a content page:
foreach (Control ctrl in this.Master.FindControl("ContentPlaceHolder1").Controls)
{
if (ctrl is TextBox)

((TextBox)ctrl).Text = "";

}