WPF Converter casting causes Visual Studio designer exception
c#, visual-studio, visual-studio-2008, wpf
Solution
I think it might happen because at some point, the converter is called with bad arguments. You can debug the call the converter in the designer by following these steps :
- start a new instance of Visual Studio
- attach to the first VS instance (Tools -> Attach to process)
- open the converter source file
- put a breakpoint in the Convert method
- reload the WPF designer in the first VS instance
That way you should be able to examine the arguments passed to the converter
Problem
A converter such as what follows will cause the 2008 visual studio designer to not display the xaml, and error out with a "Specified cast is not valid." exception. ``` public class ItemsVisibilityToGridColumnWidthConverter : IMultiValueConverter { public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture) { //THE TWO OFFENDING LINES... var itemsVisibility = (Visibility)values[0]; var orientation = (Orientation)values[1]; if (orientation == Orientation.Horizontal && itemsVisibility != Visibility.Visible) { return new GridLength(0); } return new GridLength(4, GridUnitType.Star); } public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture) { throw new NotImplementedException(); } } ``` Changing the cast to use a method such as this fixes the issue: ``` static class EnumCaster { internal static Orientation CastAsOrientation(object value) { if (value is Enum) { return (Orientation)value; } return Orientation.Horizontal; } internal static Visibility CastAsVisibility(object value) { if (value is Enum) { return (Visibility)value; } return Visibility.Visible; } } ``` My question is, wtf is wrong with the Visual Studio designer? And, is there a better way to cast these objects to their corresponding Enum in such a way that the designer doesn't throw a fit?