Trouble referencing a Resource Dictionary that contains a Merged Dictionary

Question

I have a library, CommonLibraryWpfThemes, with several Resource Dictionary XAML files in it. My Themes/Generic.xml file contains a ResourceDictionary.MergedDictionaries declaration that merges all the other files together.

Generic.xaml

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <ResourceDictionary.MergedDictionaries>
        <ResourceDictionary
            Source="/CommonLibraryWpfThemes;component/ResourceDictionaries/BrushDictionary.xaml" />
        <ResourceDictionary
            Source="/CommonLibraryWpfThemes;component/ResourceDictionaries/TextBlockDictionary.xaml" />
        <ResourceDictionary
            Source="/CommonLibraryWpfThemes;component/ResourceDictionaries/LabelDictionary.xaml" />
        <ResourceDictionary
            Source="/CommonLibraryWpfThemes;component/ResourceDictionaries/ButtonDictionary.xaml" />
        <ResourceDictionary
            Source="/CommonLibraryWpfThemes;component/ResourceDictionaries/WindowDictionary.xaml" />
    </ResourceDictionary.MergedDictionaries>
</ResourceDictionary>

In my application project, I have a reference to CommonLibraryWpfThemes, and I explicitly reference Generic.xml in my App.xaml file.

App.xaml -- FAILS

<Application
    x:Class="MyApp.App"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <Application.Resources>
        <ResourceDictionary
            Source="/CommonLibraryWpfThemes;component/Themes/Generic.xaml" />
    </Application.Resources>
</Application>

This doesn't work. I get the following error when I run my app:

System.Windows.Markup.XamlParseException occurred
  Message="Cannot find resource named '{_fadedOrangeBrush}'. Resource names are case sensitive.  Error at object 'System.Windows.Setter' in markup file 'CommonLibraryWpfThemes;component/ResourceDictionaries/WindowDictionary.xaml' Line 18 Position 13."
  Source="PresentationFramework"
  LineNumber=18
  LinePosition=13

If I place the contents of Generic.xaml into App.xaml directly, everything works fine:

App.xaml -- SUCCEEDS

<Application
    x:Class="MyApp.App"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary
                    Source="/CommonLibraryWpfThemes;component/ResourceDictionaries/BrushDictionary.xaml" />
                <ResourceDictionary
                    Source="/CommonLibraryWpfThemes;component/ResourceDictionaries/TextBlockDictionary.xaml" />
                <ResourceDictionary
                    Source="/CommonLibraryWpfThemes;component/ResourceDictionaries/LabelDictionary.xaml" />
                <ResourceDictionary
                    Source="/CommonLibraryWpfThemes;component/ResourceDictionaries/ButtonDictionary.xaml" />
                <ResourceDictionary
                    Source="/CommonLibraryWpfThemes;component/ResourceDictionaries/WindowDictionary.xaml" />
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>
</Application>

---

Maybe I'm going about this in the wrong way. My goal is to make it easy to reference all my theme resources from multiple applications without having to list out all the individual files. Is there a recommended way to do this? (Note: I'm not trying to switch between multiple themes--I just have one theme.)

As a bonus, it would be nice if someone could tell me how to reference resources in an external library without breaking the designer in Visual Studio.

Thanks.

EDIT:

I tried wrapping the ResourceDictionary in a ResourceDictionary.MergedDictionary element, but that also didn't work (I get the same error):

<Application
    x:Class="MyApp.App"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <Application.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary
                    Source="/CommonLibraryWpfThemes;component/Themes/Generic.xaml" />
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Application.Resources>
</Application>

Solution 1

Answered a similar question here earlier, see Adding a Merged Dictionary to a Merged Dictionary question.

This is an optimization bug, see Microsoft Connect / DefaultStyleKey style not found in inner MergedDictionaries:

On the creation of every object in XAML, if a default style is present (i.e. style w/ a key of Type) that style should be applied. As you can imagine there are several performance optimizations to make that (implied) lookup a light weight as possible. One of them is that we don’t look inside Resource Dictionaries unless they are flagged as “containing default Styles”. There is a bug: if all your default styles are nested in merged dictionaries three levels deep (or deeper) the top dictionary does not get flagged so the search skips it. The work around is to put a default Style to something, anything, in the root Dictionary.

So adding a dummy style to the root dictionary fixes this. Example

<Application x:Class="MyApp.App"  
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">  
    <Application.Resources> 
        <ResourceDictionary> 
            <ResourceDictionary.MergedDictionaries> 
                <ResourceDictionary 
                    Source="/CommonLibraryWpfThemes;component/Themes/Generic.xaml" /> 
                </ResourceDictionary.MergedDictionaries> 
            <!-- Dummy Style, anything you won't use goes --> 
            <Style TargetType="{x:Type Rectangle}" /> 
        </ResourceDictionary> 
    </Application.Resources> 
</Application>   

Solution 2

Check your constructor in App.xaml.cs calls InitializeComponent() - this is what merges the resource dictionaries...

Solution 3

You should not have to reference generic.xaml at all, it has built-in support. This however means that it provides default styling, which you do not set explicitly. Explicitly set styles/templates need to be attainable from explicitly referenced res dictionaries.

(EDIT for clarity)

One exception to this is the App.xaml, where defined resources become accessible by the whole app, without requiring to reference any specific resource dictionary. The resource itself, would have to be accessible by name.

The reason why this fails

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

is, I think, because you didn't wrap it in a MergedDictionary wrapper, adding it to merged dictionaries. Adding directly to resources works only for resources you declare locally, e.g. the styles, etc. themselves.

However, as I said before, you shouldn't have to merge generic.xaml anywhere, maybe you should just refactor brushes and other resources used outside styles, and merge only those resources in app.xaml.

Also note that styles do not have to be in generic.xaml to have "default style" behaviour - if a style with key equal to the type of the element is accessible to it (globally, or in local resources), then it will use the style as a default style. The generic.xaml is just a convenience.

Check this answer.

For other custom brushes, etc, you need to reference those resources explicitly.

You should also check the contents of the WindowDictionary.xaml, this error has a certain smell about it.

Comments

[Jens]

I'll start a small bounty here. Combining a few RessourceDictionaries into a Theme (and just loading this in App.xaml) seems a common enough scenario...

[Kenan E. K.]

When you merge dictionaries with app.xaml, you make the resources "global", accessible by the whole app (as the name states). Resources in app.xaml do not need to be referenced via dictionary name, only via specific resource key, I may have been unclear on that, I will clarify the answer. I usually create grouped merged dictionaries for different parts of the app and reference that dictionary in xaml as required.

[devuxer]

Thanks for clarifying your answer, but either I'm misinterpreting what you mean by "wrap it in a MergedDictionary wrapper" or that doesn't work either. I put an edit at the bottom of my question with a code sample.

[devuxer]

Doesn't work if I paste the code into a different file (MergedDictionary.xaml) either :(

[NathanAW]

This was very helpful for me. I was trying to figure out why my Pages (hosted in a Frame) weren't getting the resources defined in my App.xaml. It turns out that the constructor wasn't calling InitializeComponent. Thanks Chris!!!!

[Adrian Hand]

The bug only seems to be present in older versions of .NET 4: 4.0.30319.1008 specifically. I've seen this on XP and some un-updated Windows 7 installation.

[trapicki]

Voted down for: Link without link text; no explanation whatsoever; external content - no control over the content.

[Firo]

Link to microsoft connect is dead