Extending the style of a custom control in xaml

Question

I am developing a WPF application, and have created a custom control, we will call it 'CControl'. In the xaml document where I am designing the layout of my application. I import the style with:

xmlns:my="clr-namespace:My.Controls"

and am able to use the control just fine. The problem is I want to extend the style on CControl. In the Resource Dictionary, I am able to set:

        <Style TargetType="{x:Type my:CControl}">
            <Setter Property="Margin" Value="5 0 5 3" />
        </Style>

This applies the style to the Control, but doesn't import the style defined by CControl, so I use:

        <Style TargetType="{x:Type my:CControl}" BasedOn="{StaticResource {x:Type my:CControl}}">
            <Setter Property="Margin" Value="5 0 5 3" />
        </Style>

The problem is when my framework tries to load the xaml I get the following exception:

System.Windows.Markup.XamlParseException occurred
  Message='Provide value on 'System.Windows.StaticResourceExtension' threw an exception.' Line number '18' and line position '54'.
Source=PresentationFramework
LineNumber=18
LinePosition=54
StackTrace:
   at System.Windows.Markup.XamlReader.RewrapException(Exception e, IXamlLineInfo lineInfo, Uri baseUri)
   at System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, IXamlObjectWriterFactory writerFactory, Boolean skipJournaledProperties, Object rootObject, XamlObjectWriterSettings settings, Uri baseUri)
   at System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, Boolean skipJournaledProperties, Uri baseUri)
   at System.Windows.Markup.XamlReader.Load(XamlReader xamlReader, ParserContext parserContext)
   at System.Windows.Markup.XamlReader.Load(XamlReader reader)
   at FATPOT.Whiteboard.Report.Show() in C:\...\Report.cs
InnerException: 
   Message=Cannot find resource named 'My.Controls.CControl'. Resource names are case sensitive.
   Source=PresentationFramework
   StackTrace:
        at System.Windows.StaticResourceExtension.ProvideValueInternal(IServiceProvider serviceProvider, Boolean allowDeferredReference)
        at System.Windows.StaticResourceExtension.ProvideValue(IServiceProvider serviceProvider)
        at MS.Internal.Xaml.Runtime.ClrObjectRuntime.CallProvideValue(MarkupExtension me, IServiceProvider serviceProvider)
   InnerException: 

I have tried different ways of using BasedOn and havent gotten anything to work. Any help would be extremely useful.

Thanks

Josh

Answer 1

After trying for a day to get extend the custom control's style, I was finally able to get it to work. You can use a control by defining the namespace, but if you want to extend the control's style, you need to include the ResourceDictionary for the control. I ended up adding:

        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="pack://application:,,,/My.Project;component/Resources/CControl.xaml" />
        </ResourceDictionary.MergedDictionaries>

to my ResourceDictionary in my WPF Applications Canvas / Xaml.