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UWP: application wide TextBlock foreground crashes app when set from static resource

I went through a lot of similar questions on SO, in regards to setting the foreground of a TextBlock through a static resource, but for whatever reason my UWP application keeps crashing on me.
I am starting to believe this is a limitation of UWP? Also, no stacktrace is generated from this.
I am using Microsoft Visual Studio Community 2022 v.17.2.6
ThemeColors.xaml
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<SolidColorBrush x:Key="MyOffWhiteBrush" Color="#eeeeee" />
</ResourceDictionary>
TextBlockStyle.xaml
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Style TargetType="TextBlock">
<Setter Property="Foreground" Value="{StaticResource MyOffWhiteBrush}" />
</Style>
</ResourceDictionary>
App.xaml
<Application
x:Class="TestTextBlock.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:TestTextBlock">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="ThemeColors.xaml" />
<ResourceDictionary Source="TextBlockStyle.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
</Application>
MainPage.xaml
<Page
x:Class="TestTextBlock.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:TestTextBlock"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d">
<Grid>
<TextBlock Text="helloworld" />
</Grid>
</Page>
UPDATE #1:
If I change TextBlockStyle.xaml to this it works.
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<SolidColorBrush x:Key="_" />
<Style TargetType="TextBlock">
<Setter Property="Foreground" Value="{StaticResource MyOffWhiteBrush}" />
</Style>
</ResourceDictionary>
I don't understand why I need to declare an empty brush?

The reason for this behavior may be related to the Lookup behavior for XAML resource references and Forward references within a ResourceDictionary. You need to make sure the referenced resource must appear lexically before the resource reference when you use the resource.
I agree with #Mark W, the possible workaround is that you could define the basic resource on top of other resources.
In your scenario, it should be like this:
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="ThemeColors.xaml"/>
</ResourceDictionary.MergedDictionaries>
<Style TargetType="TextBlock">
<Setter Property="Foreground" Value="{StaticResource MyOffWhiteBrush}" />
</Style>

I don't have the answer for why... In my application, I have a number of styles - separated out into color/brushes, sizes and layouts, and then default styles... for each dictionary that references other dictionaries, I include them at the top.
ColorsAndBrushes does not have any references.
SizesAndLayout does not have any references.
DefaultStyles references the two above.
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="ColorsAndBrushes.xaml" />
<ResourceDictionary Source="SizesAndLayout.xaml" />
</ResourceDictionary.MergedDictionaries>
so for my next layer, "NamedStyles", I have have the following to the top:
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="ColorsAndBrushes.xaml" />
<ResourceDictionary Source="SizesAndLayout.xaml" />
<ResourceDictionary Source="DefaultStyles.xaml" />
</ResourceDictionary.MergedDictionaries>
I don't know if this will work better for you, but maybe feels a little better than the random empty brush. And my app.xaml references all of them. This was build on a older (AnniversaryEdition) UWP SDK, so your mileage may vary.
Good luck!
-Mark

BitmapIconSource in a ResourceDictionary.ThemeDictionaries (UWP)

I would like to change the BitmapIcon of a NavigationViewItem depending on the current Windows theme.
I've added a ResourceDictionary.ThemeDictionaries to the MainPage like that:
<Page.Resources>
<ResourceDictionary>
<ResourceDictionary.ThemeDictionaries>
<ResourceDictionary x:Key="Light">
<BitmapIconSource x:Key="ProductionBitmap"
UriSource="/Assets/Images/ProduccioBlau.png" />
</ResourceDictionary>
<ResourceDictionary x:Key="Dark">
<BitmapIconSource x:Key="ProductionBitmap"
UriSource="/Assets/Images/Produccio.png" />
</ResourceDictionary>
<ResourceDictionary x:Key="HighContrast">
<BitmapIconSource x:Key="ProductionBitmap"
UriSource="/Assets/Images/Produccio.png" />
</ResourceDictionary>
</ResourceDictionary.ThemeDictionaries>
</ResourceDictionary>
</Page.Resources>
And then in the NavigationViewItem:
<NavigationViewItem Content="Ordres fabricació"
Tag="OrdresFabricacio">
<NavigationViewItem.Icon>
<BitmapIcon UriSource="{ThemeResource ProductionBitmap}"
ShowAsMonochrome="False" />
</NavigationViewItem.Icon>
</NavigationViewItem>
But I get a squiggling line on UriSource="{ThemeResource ProductionBitmap}" saying:
The resource ProductionBitmap has an incompatible type.
What is the proper way to use a themed resource in this case?
The application compiles without errors, but I get an exception at run time when the themed resource is evaluated.

The issue is that you can't set the value of the UriSource property of the BitmapIcon in such a way. You could directly store the string value of the path of the image in the ResourceDictionary. Then using ThemeResource to get the string value.
Like this:
<ResourceDictionary>
<ResourceDictionary.ThemeDictionaries>
<ResourceDictionary x:Key="Light">
<x:String x:Key="ProductionBitmap" >/Assets/london.png</x:String>
<!--<BitmapIconSource x:Key="ProductionBitmap" UriSource="/Assets/london.png" />-->
</ResourceDictionary>
<ResourceDictionary x:Key="Dark">
<x:String x:Key="ProductionBitmap" >/Assets/paris.png</x:String>
<!--<BitmapIconSource x:Key="ProductionBitmap" UriSource="/Assets/paris.png" />-->
</ResourceDictionary>
<ResourceDictionary x:Key="HighContrast">
<x:String x:Key="ProductionBitmap" >/Assets/paris.png</x:String>
<!--<BitmapIconSource x:Key="ProductionBitmap" UriSource="/Assets/paris.png" />-->
</ResourceDictionary>
</ResourceDictionary.ThemeDictionaries>
</ResourceDictionary>
</Page.Resources>
Use it like this:
<BitmapIcon UriSource="{ThemeResource ProductionBitmap}" ShowAsMonochrome="False" />

The attachable property "ThemeDictionaries" was not found in type "ResourceDictionary"

The following code is within app.xaml on a Windows Phone 8 application. It receives the error The attachable property "ThemeDictionaries" was not found in type "ResourceDictionary". Likewise, it does not set the background. I'm trying to set the background across the entire application with the option to change it using (App.Current.Resources["BackgroundImage"] as ImageBrush).ImageSource = imgSrc; through c# code.
<Application
x:Class="MyApp.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.ThemeDictionaries>
<ResourceDictionary x:Key="Default">
<ImageBrush x:Key="BackgroundImage" ImageSource="Assets/BackgroundDefault.jpg" Stretch="UniformToFill" />
</ResourceDictionary>
<ResourceDictionary x:Key="Dark">
<ImageBrush x:Key="BackgroundImage" ImageSource="Assets/BackgroundDark.jpg" Stretch="UniformToFill" />
</ResourceDictionary>
</ResourceDictionary.ThemeDictionaries>
<local:LocalizedStrings xmlns:local="clr-namespace:MyApp" x:Key="LocalizedStrings"/>
<DataTemplate x:Key="SmallPanoramaTitle">
<ContentPresenter>
<TextBlock Text="{Binding}" FontSize="25" Margin="0,30,0,0" />
</ContentPresenter>
</DataTemplate>
</ResourceDictionary>
</Application.Resources>
<Application.ApplicationLifetimeObjects>
<!--Required object that handles lifetime events for the application-->
<shell:PhoneApplicationService
Launching="Application_Launching" Closing="Application_Closing"
Activated="Application_Activated" Deactivated="Application_Deactivated"/>
</Application.ApplicationLifetimeObjects>
</Application>

ResourceDictionary.ThemeDictionaries not available in windows phone silverlight applications.
You can use the ThemeManager library to mange your themes in WP silverlight. This is an excellent library and its available in nuget also.
See this page to understand how to use ThemeManager . You can also load custom theme files

Change slider bar color

It should be very easy to do this but I haven't found the information that I need. What I want is as simple as changing the color of the slider bar:
I'm using ModernUI and the default bar color is very similar to my background and I want to make it a bit lighter.

You should be able to change it editing the template.
Right click your Slider, Edit Template -> Edit Copy.;.
A new window will appear asking you where VS should put the XAML code for the ControlTemplate and Styles. Chek the tags and such.
Good luck!
Edit:
Ok, here it goes.
Assuming that you already have a ModernUI App, create a new folder called Assets, right click it Add -> New Item... -> ModernUI Theme. Call it whatever you like it.
Inside the newly created XAML file insert these SolidColorBrush under the AccentColor Color tag:
<SolidColorBrush x:Key="SliderSelectionBackground" Color="Red" />
<SolidColorBrush x:Key="SliderSelectionBorder" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBackground" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBackgroundDisabled" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBackgroundDragging" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBackgroundHover" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBorder" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBorderDisabled" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBorderDragging" Color="Red" />
<SolidColorBrush x:Key="SliderThumbBorderHover" Color="Red" />
Each one of these represents a state of the Thumb (the slider "rectangle"). After that open your App.xaml file and include your theme there (this is what my file looks like):
<Application x:Class="ModernUIApp1.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
StartupUri="MainWindow.xaml">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="/FirstFloor.ModernUI;component/Assets/ModernUI.xaml" />
<ResourceDictionary Source="/FirstFloor.ModernUI;component/Assets/ModernUI.Light.xaml"/>
<ResourceDictionary Source="/Assets/ModernUI.Theme1.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
</Application>
The <ResourceDictionary Source="/Assets/ModernUI.Theme1.xaml" /> bit represents my theme.
Setting all the colors to Red, this is what it looked like:
I guess that's more clear!
Hope you like it.
EDIT:
It will change when you apply your theme. But, as you're familiar with styles, I'm sending the complete template. What you can do is create a UserDictionary with only this template and when you you want to use it, change the slider Template property. You'll want to change only the Thumb Tags. Pastebin code
And if you want to change only THIS one put the template between <Windows.Resources> or <Slider.Resources> - Another option would be create your own control

I found two approaches:
You can customize your slider by insert corresponding brushes in
appropriate Slider.Resources section.
You can add brushes to separate xaml file with dictionary and then
merge it with corresponding slider in the Slider.Resources. In some cases it fits better because you can change colors of few controls at once.
Any does not need to changing of the control's template.
Both approaches are presented below:
Page1.xaml
<Grid Style="{StaticResource ContentRoot}">
<StackPanel>
<!-- Slider with default theme and colors from ModernUI -->
<Slider/>
<!-- Slider with custom colors from approach 1 -->
<Slider>
<Slider.Resources>
<SolidColorBrush x:Key="SliderSelectionBackground" Color="Green" />
<SolidColorBrush x:Key="SliderSelectionBorder" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBackground" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBackgroundDisabled" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBackgroundDragging" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBackgroundHover" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBorder" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBorderDisabled" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBorderDragging" Color="Green" />
<SolidColorBrush x:Key="SliderThumbBorderHover" Color="Green" />
</Slider.Resources>
</Slider>
<!-- Slider with custom colors from approach 2 -->
<Slider>
<Slider.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="Dictionary1.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Slider.Resources>
</Slider>
</StackPanel>
</Grid>
Dictionary1.xaml
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<SolidColorBrush x:Key="SliderSelectionBackground" Color="Blue" />
<SolidColorBrush x:Key="SliderSelectionBorder" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBackground" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBackgroundDisabled" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBackgroundDragging" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBackgroundHover" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBorder" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBorderDisabled" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBorderDragging" Color="Blue" />
<SolidColorBrush x:Key="SliderThumbBorderHover" Color="Blue" />
</ResourceDictionary>
As result you get following:

Foreground property is used to fill the "completed" part of the slider with a particular color. (Background does the uncompleted part.)
<Slider Value="40" Maximum="100" Foreground="Red" />

Here you have the templates you should use: Slider Styles and Templates
The property you are looking to edit is the TrackBackground.BackGround.
If you define a style for this control template and put it either in you app.xaml or in the window.resources or in any other file, as long as you give it a key you can use it in a specific slider through the "Style" property of that slider using that same key.

Windows 8.1 Store/Phone Apps.
Add this to the App.xaml and change the color values to your liking:
<ResourceDictionary>
<ResourceDictionary.ThemeDictionaries>
<ResourceDictionary x:Key="Default">
<SolidColorBrush x:Key="SliderTrackDecreaseBackgroundThemeBrush" Color="#FFFF0000" />
<SolidColorBrush x:Key="SliderTrackDecreasePointerOverBackgroundThemeBrush" Color="#FF00FF00" />
<SolidColorBrush x:Key="SliderTrackDecreasePressedBackgroundThemeBrush" Color="#FF0000FF" />
</ResourceDictionary>
<ResourceDictionary x:Key="Light">
</ResourceDictionary>
<ResourceDictionary x:Key="HighContrastBlack">
</ResourceDictionary>
<ResourceDictionary x:Key="HighContrastWhite">
</ResourceDictionary>
</ResourceDictionary.ThemeDictionaries>
</ResourceDictionary>
You probably only want to change the slider for the default theme and probably only the three color values shown above. For all colors / resources that you can change, see this link at MSDN: Slider styles and templates.

For what it's worth, the only way I could change the Slider Thumb color on Win10 UWP for Phone was to overwrite the System Foreground brush. (You can also apparently completely re-template the whole Slider)
So, I put into my App.xaml
<Application
x:Class="App1.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:App1"
RequestedTheme="Dark">
<Application.Resources>
<SolidColorBrush x:Key="SystemControlForegroundAccentBrush" Color="White" />
</Application.Resources>
</Application>
The addition to Application.Resources is the really important thing here. It's where we're overwriting the Foreground color for ALL common elements, like Checkbox, ContentDialog, ProgressRing, etc.... So, that's the downside to this method too.
Changing the Thumb color on a Slider is a known problem point for XAML UWP. Microsoft has plans to make it easier in the immediate future.

Load control style from separate file in wpf

I have the following style added to my Windows.Resources
<Window.Resources>
...
<!--A Style that extends the previous TextBlock Style-->
<!--This is a "named style" with an x:Key of TitleText-->
<Style BasedOn="{StaticResource {x:Type TextBlock}}"
TargetType="TextBlock"
x:Key="TitleText">
<Setter Property="FontSize" Value="26"/>
<Setter Property="Foreground">
<Setter.Value>
<LinearGradientBrush StartPoint="0.5,0" EndPoint="0.5,1">
<LinearGradientBrush.GradientStops>
<GradientStop Offset="0.0" Color="#90DDDD" />
<GradientStop Offset="1.0" Color="#5BFFFF" />
</LinearGradientBrush.GradientStops>
</LinearGradientBrush>
</Setter.Value>
</Setter>
</Style>
...
</Window.Resources>
I have a lot of those styles in my xaml code and I would like to save each component style to an extra file (not an external file).. for example all the styles related to TextBlocks should be in a file called TextBlockStyles.xaml
How would I do this in wpf?
How do I link the style in my project ?
Thanks in advance

You use merged resource dictionaries
In you app.xaml you would use
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary
Source="/Your.Assembly.Name;component/TextBlockStyles.xaml"/>
... other dictionaries here
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
or directly into a UserControl would be
<UserControl.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary
Source="/Your.Assembly.Name;component/TextBlockStyles.xaml"/>
... other dictionaries here
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</UserControl.Resources>
You can shorten Source="..." to just Source="TextBlockStyles.xaml" if the file is in the same assembly and in the root of the project, or alternatively Source="Styles\TextBlockStyles.xaml" if you put the resource dictionary into the folder Styles.

Use case: you have a user control called MyView.xaml with a button. You want to style the button with an external XAML file.
In MyView.xaml:
<User Control ...namespaces...>
<UserControl.Resources>
<ResourceDictionary>
...converters...
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="MyButton.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</UserControl.Resources>
...the rest of the control...
</UserControl>
In MyButton.xaml:
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:MSDNSample">
<Style x:Key="FooButton" TargetType="{x:Type Button}">
<Setter Property="Background" Value="Pink" />
</Style>
</ResourceDictionary>
Back to MyView.xaml ("the rest of the control"):
<Button Style="{StaticResource FooButton}">
Hello World
</Button>

In Solution Explorer Right Click on your Project Select Add After that click on Resource Dictionary...
Choose name and add to your project.
Open App.xaml
Add This Code in Application Tag
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="YourStyle.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
In YourStyle.xaml :
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:APPNAME">
<Style x:Key="ButtonStyle" TargetType="{x:Type Button}">
<Setter Property="Background" Value="Pink" />
</Style>
</ResourceDictionary>

you are looking for the dynamic resources. well the best way is to load and marge the dictionary in the resources. application or either on control page.
here is a good sample for it.
http://blogs.msdn.com/b/wpfsdk/archive/2007/06/08/defining-and-using-shared-resources-in-a-custom-control-library.aspx
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="Dictionary1.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
this.Resources.MergedDictionaries.Add(Smyresourcedictionary);

Simply, go to your Window (example: MaindWindow.xaml) where you want to include the resource from the outer file and use MergedDictionaries principle to refer to that file:
<Window x:Class="UseMergedResource.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
Title="MainWindow"
Height="600"
Width="600">
<Window.Resources>
<!-- DECLARING MERGED DICTIONARY -->
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source='Merged/BrushResources.xaml' />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
<!---------------------------------->
</Window.Resources>
<StackPanel>
<Rectangle Width='200'
Height='100'
Fill='{StaticResource PrimaryBrush}' /> <!-- USAGE HERE -->
</StackPanel>
</Window>
From above Merged/BrushResources.xaml is the location of the resource file, which is located under the folder called Merged.
Now if you are wondering what should be the declaration syntax in the outer file, check this:
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<!-- Location for application brushes -->
<SolidColorBrush x:Key='BorderBrush'
Color='Orange' />
<SolidColorBrush x:Key='HighLightBrush'
Color='LightBlue' />
<SolidColorBrush x:Key='PrimaryBrush'
Color='Pink' />
<SolidColorBrush x:Key='AccentBrush'
Color='Yellow' />
</ResourceDictionary>
If you want to make the resource available through all application (visible in all your windows) then declare in the App.xaml resources section.