Passing data through XAML into VB - wpf

Question

ORIGINAL (Solved by Clemens):
I have code (below) where I am trying to pass a parameter through XAML into VB. This gives it an error code " 'tabText' property was already registered by 'customTabPanel' " and I am not sure what I should do here as this is my first attempt takling this problem
NEW:
This still doesn't pass the text through properly and I have no idea why. Any help will be appreciated.
VB:
Public Class customTabPanel
Inherits Grid
Dim workSpaceAssociation As Grid
Public ReadOnly TextProperty As DependencyProperty = DependencyProperty.Register("tabText", GetType(String), GetType(customTabPanel), New PropertyMetadata(String.Empty))
Public Property tabText() As String
Get
Return DirectCast(GetValue(TextProperty), String)
End Get
Set(value As String)
SetValue(TextProperty, value)
End Set
End Property
Sub New()
Me.Height = 20
Me.Background = New SolidColorBrush(Color.FromRgb(27, 27, 28))
Dim textBlock As New TextBlock
textBlock.Foreground = New SolidColorBrush(Colors.White)
textBlock.Text = tabText
textBlock.Width = 100
textBlock.Padding = New Thickness(10, 0, 25, 0)
Dim closeWorkspace As New TextBlock
closeWorkspace.HorizontalAlignment = Windows.HorizontalAlignment.Right
closeWorkspace.Text = ""
closeWorkspace.Foreground = New SolidColorBrush(Colors.White)
closeWorkspace.Height = 15
closeWorkspace.Width = 15
closeWorkspace.FontFamily = New FontFamily("Segoe UI Symbol")
'add'
Me.Children.Add(textBlock)
Me.Children.Add(closeWorkspace)
Me.Width = textBlock.Width
Me.Margin = New Thickness(5, 0, 0, 0)
Me.HorizontalAlignment = Windows.HorizontalAlignment.Left
End Sub
Sub SetText(ByVal t As String)
tabText = t
End Sub
Function GetText() As String
Return tabText
End Function
End Class
XAML:
<ThisIsAwsome:customTabPanel tabText="Start Screen" />

Answer 1

The dependency property field has to be declared as Shared:
Public Shared ReadOnly TextProperty As DependencyProperty = ...
In order to get notified about updated property values, you would also have to register a PropertyChangedCallback with the property's metadata:
Public Shared ReadOnly TextProperty As DependencyProperty =
DependencyProperty.Register(
"tabText", GetType(String), GetType(customTabPanel),
New PropertyMetadata(
String.Empty, New PropertyChangedCallback(AddressOf TabTextChanged)))
In the TabTextChanged callback you would set your TextBlock's Text property (no idea though if it's valid VB):
Private Shared Sub TabTextChanged(
ByVal d As DependencyObject, ByVal e As DependencyPropertyChangedEventArgs)
Dim panel As customTabPanel = CType(d, customTabPanel)
panel.textBlock.Text = CType(e.NewValue, String)
End Sub
You'll find a detailed explanation in the Custom Dependency Properties article on MSDN.