I was creating this XAML to hold the design of all the controls in a library as a theme (generic.xaml). After a while it just got too big and so I had to use merged dictionaries to split the file into smaller parts.

First problem is that you can't just use the name of the file as the source of a ResourceDictionary, you need to specify the assembly name kind of like this:
<ResourceDictionary Source="/Library.Namespace;component/Themes/OneOfMyControls.xaml" />
Notice the keyword component, which is NOT part of the folder or namespace structure.

The second problem is when you want to use merged dictionaries and then reuse a style key, for example, that you would expect to just place directly in generic.xaml or in the first merged dictionary. You will soon get a "Resource not found" error. Googling, one notices a lot of people having the same problem, but only in the generic.xaml/themes scenario. The solution is to add the common style file as a merged dictionary in each of the dictionaries merged in generic.xaml. That means that if you have 5 controls that use the same style and you have a xaml file for each control and one for the style, you need to add a MergedDictionaries entry in each of the 5 control files and merge the style xaml there.


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