Resources not resolving from ResourceDictionaries

Question

I'm having problems resolving Resources from my ResourceDictionaries.

I decided to refactor my rather large ResourceDictionary into individual dictionary files, organized into subfolders.

I have a ResourceLibrary.xaml under Resources:

<ResourceDictionary x:Class="MyProject.Resources.ResourceLibrary"
                xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
   <ResourceDictionary.MergedDictionaries>
     <!-- Colours -->
     <ResourceDictionary Source="Colors/ConnectedCellColor.xaml" />
     <!-- Brushes -->
     <ResourceDictionary Source="Brushes/ConnectorCellBrush.xaml" />
     <!-- Control Templates -->
     <ResourceDictionary Source="ControlTemplates/ConnectorCellTemplate.xaml" />
     <!-- Base Styles -->
     <ResourceDictionary Source="BaseStyles/ConnectorBaseStyle.xaml" />
   </ResourceDictionary.MergedDictionaries>
</ResourceDictionary>

The class is there for a reason, in the code behind, I can add [Export(typeof (ResourceDictionary))] so MEF can find it.

I have a View: (simplified)

<UserControl x:Class="MyProject.ConnectorCellView"
         Style="{StaticResource ConnectorBaseStyle}"
</UserControl>

ConnectorBaseStyle:

<ResourceDictionary>
   <Style x:Key="ConnectorBaseStyle" TargetType="UserControl">
      <Setter Property="Template" Value="{StaticResource ConnectorCellTemplate}" />
   </Style>
</ResourceDictionary>

The template has StaticResources to try and get a Brush and a colour.

All of these StaticResources will not resolve any more.

I thought it might have been an order issue, but since these resources are contained in a plugin to my main program, I use MEF and ImportMany to get all the exported ResourceDictionaries, and in my Caliburn.Micro bootstrapper:

  public void OnImportsSatisfied()
  {
     foreach (ResourceDictionary resourceDictionary in ResourceDictionaries)
     {
        Application.Resources.MergedDictionaries.Add(resourceDictionary);
     }
  }

(Neat trick I found somewhere)

I can actually run my program, and when that view is created it throws an exception when trying to set the style:

System.InvalidCastException
Unable to cast object of type 'MS.Internal.NamedObject' to type System.Windows.FrameworkTemplate'.

The only information I've found relating to this has to do with the order resources are defined, but from the order I have them in ResourceLibrary, it should work.

When the exception is thrown, I can examine Application.Current.Resources.MergedDictionaries, and see the resources.

I've tried various ways of specifying the Source in ResourceLibrary

<ResourceDictionary Source="/MyProject;component/Resources/BaseStyles/ConnectorBaseStyle.xaml" />

etc, no effect on finding them. These resources are only used by the plugin code.

The only thing that seemed to work was changing all the StaticResources to DynamicResources

which doesn't make sense to me, if it is an order issue, why would Static work when they're all in the same file?

Some of my styles used BasedOn, and they don't work with DynamicResource.

Can you help me understand why this is happening, and how to make it work?

John Bowen · Accepted Answer · 2013-02-04 17:18:23Z

1

It is an ordering problem but not with the ordering of your merging - it's with the order of loading. Here's basically what happens when the ResourceLibrary dictionary loads:

ConnectedCellColor instantiates
ConnectedCellColor loads into ResourceLibrary
ConnectorCellBrush instantiates
ConnectorCellBrush loads into ResourceLibrary
ConnectorCellTemplate instantiates
ConnectorCellTemplate loads into ResourceLibrary
ConnectorBaseStyle instantiates
ConnectorBaseStyle loads into ResourceLibrary

The problem here is that where before with your single file you had a single instantiation step, you now have that broken up into multiple steps, each of which happen independently. When ConnectorBaseStyle is instantiated ConnectorCellTemplate has been loaded but ResourceLibrary's contents aren't known to ConnectorBaseStyle at this point. With DynamicResource this isn't a problem because those references can just resolve at step 8, but StaticResource requires immediate resolution at step 7.

The simplest fix is to use Dynamic wherever you can. For places that require Static (like BasedOn) you need to guarantee that the resource will be available during instantiation, either by also merging, for example, ConnectorCellTemplate into ConnectorBaseStyle, or by merging everything that's needed into App.xaml which is available to everything. This can make things complicated and hard to manage as you get more files and do merging into multiple places but at least the resource system is smart enough to recognize duplicates so in the case above you would still only get a single instance of ConnectorCellTemplate even though it is being merged at two places.

answered Feb 4, 2013 at 17:18

John Bowen

24.5k4 gold badges61 silver badges56 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Kage Over a year ago

Not sure I understand this fully. As far as I knew, ResourceLibrary was loaded once my app had initialized, as I could see the resources in the debugger. Once the view is created, it seems to me if the BaseStyle is in the App's Resources, it should resolve...

Collectives™ on Stack Overflow

Resources not resolving from ResourceDictionaries

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related