Find only the controls i want on a form

[F Scheltens]

Hi,

i'm trying to write some code to locate and clear the textboxes on a WPF form. However i'm trying to do so from outside the class, so i can reuse the code later. The problem is that at this time it's not working very well. For example: if I only add controls to the list with no children, i get the textblock inside the button instead of the button. I only want the controls as i place them on the form, so i can reset them if needed.
Now i have two questions:
1- Should i just filter on the type of the control to pick what goes on the list, or is there a better way of doing it?
2- I ended up with a list<of DependencyObject>. Each element of this list contained a control. Can i address the properties of the control in the list directly, or do i first need to convert the item back to a control?

Option Strict On
Public Class Utilities
    Public Shared Sub ResetAllControls(ByVal form As Control)
        Dim listofControls As List(Of DependencyObject) = GetAllControls(form)
        For i As Integer = 0 To listofControls.Count - 1
            Dim v As DependencyObject = listofControls(i)
            If (TypeOf (v) Is TextBox) Then
                Dim tb As TextBox = CType(v, TextBox)
                tb.Text = ""
            End If
        Next
    End Sub

    Private Shared Function GetAllControls(ByVal parentcontrol As DependencyObject) As List(Of DependencyObject)
        Dim listofControls As New List(Of DependencyObject)
        Try
            If (parentcontrol Is Nothing) Then
                Throw New ArgumentNullException(parentcontrol.ToString, "Argument of GetAllControls was NULL")
            End If
            Dim i, count As Integer

            count = VisualTreeHelper.GetChildrenCount(parentcontrol)
            For i = 0 To count - 1
                Dim child As DependencyObject = VisualTreeHelper.GetChild(parentcontrol, i)

                'if (TypeOf(child) is TextBox) then 'Should i just go with this???
                If (CBool(VisualTreeHelper.GetChildrenCount(child))) Then
                    listofControls.AddRange(GetAllControls(child))
                Else
                    listofControls.Add(child)
                End If
            Next
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
        Return listofControls
    End Function
End Class