How to Convert this generic method from C# to VB.Net

Question

I have the following code block in C#

private void Synchronize<T>(TextSelection selection, DependencyProperty property, Action<T> methodToCall)
{ 
    object value = selection. GetPropertyValue(property) ;
    if ( value != DependencyProperty. UnsetValue) methodToCall((T) value) ;
} 

That I have converted to VB.

Private Sub Synchronize(Of T)(ByVal selection As TextSelection, ByVal [property] As DependencyProperty, ByVal methodToCall As Action(Of T))
    Dim value As Object = selection.GetPropertyValue([property])
    If value IsNot DependencyProperty.UnsetValue Then
        methodToCall(DirectCast(value, T))
    End If
End Sub

The calling method look like:

Synchronize(Of Double)(selection, TextBlock.FontSizeProperty, AddressOf SetFontSize)
Synchronize(Of FontWeight)(selection, TextBlock.FontSizeProperty, AddressOf SetFontWeight)
Synchronize(Of FontStyle)(selection, TextBlock.FontStyleProperty, AddressOf SetFontStyle)
Synchronize(Of FontFamily)(selection, TextBlock.FontFamilyProperty, AddressOf SetFontFamily)
Synchronize(Of TextDecorationCollection)(selection, TextBlock.TextDecorationsProperty, AddressOf SetTextDecoration)

My problem is with the DirectCast call; if my delegate argument can be a simple type (integer, double, etc) or an object. DirectCast doesn't like the simple data types an InvalidCastException is thrown when I try to cast to a double. Does anyone have a suggested solution to this problem? I've also tried TryCast, but it doesn't like my (of T) and says it must be class contstrained.

Thanks all!

Ryan

Answer 1

Looking at the errors you're seeing, it sounds like you may need to add a constraint on your T handle limit it to a class in order for the TryCast to be used.

I'm not really familiar with VB's TryCast method (or DirectCast, for that matter), but something like this might help [note that (Of T) -> (Of T as Class) ]:

Private Sub Synchronize(Of T as Class)(ByVal selection As TextSelection, ByVal [property] As DependencyProperty, ByVal methodToCall As Action(Of T)) 
    Dim value As Object = selection.GetPropertyValue([property]) 
    If value IsNot DependencyProperty.UnsetValue Then 
        methodToCall(TryCast(value, T)) 
    End If 
End Sub 

Answer 2

Use CType instead of TryCast/DirectCast. It should work like the casting in C# :

methodToCall(CType(value, T))

Answer 3

Try CType() instead of DirectCast().

Answer 4

You can put multiple constraints on t

I believe the syntax is something like:

Private Sub Synchronize(Of T as {Class, Integer, Double})