Error when binding using markup extensions: Unknown property encountered while parsing a Markup Extension
It's a bug that can occur with nested MarkupExtensions. Try putting your custom Markup into a separate DLL/Project or use property element syntax.
WPF doesn't handle nested markup extensions too well. To overcome this, you can use your markup extension as an element. It's a bit clumsy and harder to read, but it works:
<RadioButton GroupName="F1" Content="Filter Number One"> <RadioButton.IsChecked> <Binding Path="Filter"> <Binding.Converter> <local:TrueWhenEqual To={x:Static local:ViewModelClass.Filter1} /> </Binding.Converter> </Binding> </RadioButton.IsChecked></RadioButton>
Another way would be to declare your converter and use it as a static resource:
<Window.Resources> <local:TrueWhenEqual To={x:Static local:ViewModelClass.Filter1} x:Key="myConverter" /></Window.Resources><RadioButton GroupName="F1" Content="Filter Number One" IsChecked="{Binding Filter, Converter={StaticResource myConverter}}" />
I encountered the same bug on a machine with .NET 4.6 installed. As soon as I updated to the .NET 4.7 (Developer Pack) this error gone without any code changes.