.net core WPF System.Windows.ResourceDictionary warning miss details

[endink]

• .NET Core Version: 3.1
• Windows version: Windows 10

Problem description:

When we debug or Run the WPF application it works fine but in output window so many lines are coming with warning

System.Windows.ResourceDictionary Warning: 9 : Resource not found;

It does not provide any details to tell me which resource missed.
And this warning causes the UI to become slower and slower at debugging time

the output window:

the same message in diagnostic tool window"

How can i get the full output information?

[ActSabke]

After migrating our .net 461 wpf application we get the same error.
Is there any way to detect which resource dictionary throws this error?

[fabiant3]

@endink - can you please attach a minimal repro?

[TysonMN]

I can provide a reproduction that is rather minimal.

ZIP of reproduction

This reproduction depends on Material Design in XAML, which is how I recently encountered this problem. I am sure that a smaller / simpler reproduction is possible without this dependency, but I have yet to figure out how.

Reproduction steps

1. Download ZIP
2. Unzip
3. Open the solution file
4. Run the application (which targets .NET Core 3.1)
5. Click anywhere (see GIF below)

Actual Behavior when targeting .NET Core 3.1

To the "Output" window is added two copies of

System.Windows.ResourceDictionary Warning: 9 : Resource not found

Better Behavior when targeting .NET Framework 4.7.2

To the "Output" window is added these two lines:

System.Windows.ResourceDictionary Warning: 9 : Resource not found; ResourceKey='PrimaryHueMidBrush'
System.Windows.ResourceDictionary Warning: 9 : Resource not found; ResourceKey='MaterialDesignCheckBoxOff'

Desired Behavior for all targets

Clearly the behavior when targeting .NET Framework 4.7.2 is better than when targeting .NET Core 3.1. However, I was hoping that both cases would provide more information.

Consider the missing resource PrimaryHueMidBrush. I happen to know (after too much debugging) that the resource with that key has type Brush and is for the property Foreground of the Slider control in MainWindow.xaml on line 7.

MainWindow.xaml:

<Window x:Class="WpfApp2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:md="http://materialdesigninxaml.net/winfx/xaml/themes"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <md:DialogHost>
    <md:DrawerHost IsLeftDrawerOpen="{Binding IsChecked}">
      <Slider />
    </md:DrawerHost>
  </md:DialogHost>
</Window>

As such, the most direct way to avoid the PrimaryHueMidBrush missing resource is to directly specify a foreground color for the Slider. For example replace <Slider /> with <Slider Foreground="Blue" />. Then there will be one less message about a missing resource (and specifically no missing resource message for PrimaryHueMidBrush when targeting .NET Framework 4.7.2).

Can the missing resource message be improved so that in the above code, the message about the missing resource PrimaryHueMidBrush would also include the following information?

• Brush
• Forground
• Slider
• MainWindow.xaml
• Line 7

Unexpected delay

In my reproduction, why do the lines about missing resources only appear after clicking? I expected that they would appear during application load. Maybe the foreground color of the Slider is a different color when the DialogHost is open. However, why are there no lines about missing resources when starting the application with the DialogHost closed?

Additional information

For the specific case of this reproduction, the "correct" fix to avoid missing those two resources is to comment in the commented out line in App.xaml. Then PrimaryHueMidBrush is set because of the function call on this line and MaterialDesignCheckBoxOff is set because of the function call on this line.

<Application x:Class="WpfApp2.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:materialDesign="http://materialdesigninxaml.net/winfx/xaml/themes"
             StartupUri="MainWindow.xaml">
  <Application.Resources>
    <ResourceDictionary>
      <ResourceDictionary.MergedDictionaries>
        <!--<materialDesign:BundledTheme BaseTheme="Light" PrimaryColor="DeepPurple" SecondaryColor="Lime" />-->
        <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.Defaults.xaml" />
      </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
  </Application.Resources>
</Application>