The current top-hit on WPF ResourceDictionary on Google has a minor error in the usage of WPF’s ResourceDictionary class. Hopefully I can save someone the ten minutes of hate I had while searching for the cause of the strange error the Studio threw at me.

Wrong:

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="TextStyle.xaml" />
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
    <!-- other styles can appear in the resource dictionary too -->
    <Style TargetType="{x:Type Button}"
           x:Key="ButtonStyle">
        <Setter Property="Background"
                Value="#feca00" />
    </Style>
</Application.Resources>

Right:

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="TextStyle.xaml" />
        </ResourceDictionary.MergedDictionaries>
        <!-- other styles can appear in the resource dictionary too -->
        <Style TargetType="{x:Type Button}"
               x:Key="ButtonStyle">
            <Setter Property="Background"
                    Value="#feca00" />
        </Style>
    </ResourceDictionary>
</Application.Resources>

Note the difference in where the additional <Style>s go.

WPF binding is great, but directly binding the View to the Model has its limitations. As soon as the Model’s and the View’s structure diverge (which happens quite fast, I was surprised myself) the direct binding approach falls apart. The first example where I hit this was a tree of items which should be displayed and selected in a (decorated) list. Data binding just doesn’t cut it. The solution lies in creating a so called ViewModel.

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