Public Shared Function VirtualKeyFromKey ( _
    key As Key _
) As Integer

Dim key As Key
Dim returnValue As Integer

returnValue = KeyInterop.VirtualKeyFromKey(key)

public static int VirtualKeyFromKey(
    Key key
)

public:
static int VirtualKeyFromKey(
    Key key
)

public static function VirtualKeyFromKey(
    key : Key
) : int

You cannot use methods in XAML.