I have a custom panel control that I'm trying to dynamically add controls within. When I run the application the static and dynamically added controls show up perfectly, but the dynamic controls do not appear within the visual studio designer. Only the controls placed declaratively in the XAML appear. I'm currently adding the dynamic control in the CreateUIElementCollection override, but I've also tried this in the constructor without success.

Public Class CustomPanel1
Inherits Panel

Public Sub New()

End Sub

Protected Overrides Function MeasureOverride(ByVal availableSize As System.Windows.Size) As System.Windows.Size
    Dim returnValue As New Size(0, 0)

    For Each child As UIElement In Children
        child.Measure(availableSize)
        returnValue.Width = Math.Max(returnValue.Width, child.DesiredSize.Width)
        returnValue.Height = Math.Max(returnValue.Height, child.DesiredSize.Height)
    Next

    returnValue.Width = If(Double.IsPositiveInfinity(availableSize.Width), returnValue.Width, availableSize.Width)
    returnValue.Height = If(Double.IsPositiveInfinity(availableSize.Height), returnValue.Height, availableSize.Height)

    Return returnValue
End Function

Protected Overrides Function ArrangeOverride(ByVal finalSize As System.Windows.Size) As System.Windows.Size
    Dim currentHeight As Integer
    For Each child As UIElement In Children
        child.Arrange(New Rect(0, currentHeight, child.DesiredSize.Width, child.DesiredSize.Height))
        currentHeight += child.DesiredSize.Height
    Next

    Return finalSize
End Function

Protected Overrides Function CreateUIElementCollection(ByVal logicalParent As System.Windows.FrameworkElement) As System.Windows.Controls.UIElementCollection
    Dim returnValue As UIElementCollection = MyBase.CreateUIElementCollection(logicalParent)

    returnValue.Add(New TextBlock With {.Text = "Hello, World!"})

    Return returnValue
End Function

Protected Overrides Sub OnPropertyChanged(ByVal e As System.Windows.DependencyPropertyChangedEventArgs)
    MyBase.OnPropertyChanged(e)
End Sub
End Class

And my usage of this custom panel

<Window x:Class="MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:CustomPanel"
Title="MainWindow" Height="364" Width="434">

<local:CustomPanel1>
    <CheckBox />
    <RadioButton />
</local:CustomPanel1>

</Window>