WPF: Style based on another one in a separate assembly

Question

Assembly A - ResourceDictionary contains StyleA style.
Assembly B - ResourceDictionary.MergedDictionaries to merge resources from Assembly A into B.

I would like to create a style in Assembly B "based on" StyleA. Is it possible?

I am trying to create this style:

<Style x:Key="StyleB" BasedOn="{StaticResource StyleA}">
   <Setter Property="Button.Foreground" Value="Khaki"/>
</Style>

But I get a XamlParseException exception at run-time, if I use StyleB:

Cannot convert the value in attribute 'Style' to object of type 'System.Windows.Style'. Can only base on a Style with target type that is base type 'IFrameworkInputElement'. Error at object 'System.Windows.Controls.Button' in markup file 'SamSeekApp;component/mainwindow.xaml'

score 42 · Accepted Answer · answered Apr 01 '09 at 00:08

42

Try adding TargetType="{x:Type Button}" to your 'StyleB'.

answered Apr 01 '09 at 00:08

Richard Davis

496
5
2

Thanks Richard. It works! But why doesn't it work without specifying the type? – Gus Cavalcanti Apr 01 '09 at 21:53
Sorry, I'm not sure why it is needed here. – Richard Davis Apr 03 '09 at 18:51
6

Because WPF needs to know what type your style is targeting, so it can check the properties, etc you override. Even if the parent (BasedOn) style declares the target type, you still need to redeclare the target type in the child style – Xcalibur Mar 14 '11 at 16:15
this is awesome :-) – Simon_Weaver Jan 22 '17 at 05:47
note this also work when defining a style 'in place' for a control, which you may need to do to set DataTriggers on it – Simon_Weaver Jan 22 '17 at 05:52

WPF: Style based on another one in a separate assembly

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