What is so special about Generic.xaml?

wpf xaml themes
devuxer picture devuxer · Aug 4, 2009 · Viewed 52.6k times · Source

I've been trying to figure out how to organize my ResourceDictionary files for reuse and sharing with other members of my team.

I keep coming across "Generic.xaml", but if I look on MSDN for Generic.xaml or just do a Google search, I only seem to get blog posts and forum questions that happen to mention it--I can't seem to hit upon anything really authoritative and clear.

What is the difference between Generic.xaml and MyRandomlyNamedResourceDictionary.xaml? It seems like either way, I have to reference ResourceDictionaries stored in libraries with the Source attribute. E.g.,:

<Application.Resources>
    <ResourceDictionary
        Source="/CommonLibraryWpfThemes;component/Themes/Generic.xaml"
</Application.Resources>

So what advantage does Generic.xaml provide exactly? Does it have any purpose if I'm not trying to give my application multiple "looks" (i.e., if I have only one theme)?

Answer

Phil Devaney picture Phil Devaney · Aug 5, 2009

Every Control in WPF has a default Style that provides, among other things, the Control's default ControlTemplate. WPF looks for the default style in a special resource dictionary in the Themes folder in the same assembly as the control. The key for the default style is provided by the Control.DefaultStyleKey dependency property, the default value of which is overridden in each sub-class of Control.

The name of the resource dictionary depends on the current Windows theme e.g. on Vista using the Aero theme, the dictionary is called Aero.NormalColor.xaml, on XP using the default theme it is Luna.NormalColor.xaml. If the style is not found in the theme dictionary, it looks in Generic.xaml i.e for controls whose look doesn't depend on the theme.

This only applies to any custom controls you have defined i.e. classes derived from Control, directly or indirectly. You can change the default style for a standard control by deriving from it and calling DefaultStyleKeyProperty.OverrideMetadata in the static constructor, but you then have to supply the full style including ControlTemplate.

Note that you can tell WPF to look in an external assembly for your default style by using the ThemeInfo attribute. The external assembly must be named <YourAssembly>.<ThemeName>.dll e.g. PresententationFramework.Aero.dll.

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