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C# WPF: The Resource Dictionary does not load at run time, but displays correctly in the designer

Problem: The resource dictionary does not load at run time, but displays correctly in the designer. If I change the color in Dark.xaml to green, I can notice in the designer that my Window background (Layout.xaml) turns green. but when I compile the project in Debug mode, the background is just transparent !!
What I have tried in App.xaml:
<Applicationxmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:StackOverflow" x:Class="StackOverflow.App">
<Application.Resources>
<ResourceDictionary Source="#"/>
</Application.Resources>
</Application>
And:
<Applicationxmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:StackOverflow" x:Class="StackOverflow.App">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="#"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
</Application>
In the source value, I tried these 3 possibilities:
Theme/Dark.xaml
/StackOverflow;component/Theme/Dark.xaml
pack://application:,,,/StackOverflow;component/Theme/Dark.xaml
App.xaml.cs:
Current.ShutdownMode = ShutdownMode.OnExplicitShutdown;
Window Window = Server.Status() is StatusCode.OK ? new Layout() : new Login();
Window.ShowDialog();
Current.Shutdown();
Dark.xaml:
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" x:Class="StackOverflow.Theme.Dark" xmlns:local="clr-namespace:StackOverflow.Theme">
<SolidColorBrush x:Key="Layout.Background">Red</SolidColorBrush>
</ResourceDictionary>
Dark.xaml: File Properties
Build Action: Page
Copy to Output Directory: Do not copy
Custom Tool: XamlIntelliSenseFileGenerator
Custom Tool Namespace:
Dark.cs:
namespace StackOverflow.Theme {
public partial class Dark : ResourceDictionary {
public Dark(){
InitializeComponent();
}
}
}
Dark.cs: File Properties
Build Action: Compile
Copy to Output Directory: Do not copy
Custom Tool:
Custom Tool Namespace:
Note: These two files (Dark.xaml / Dark.cs) are nested using the File Nesting extension (Keith Wilson).
Layout.xaml:
<Window
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"
xmlns:local="clr-namespace:StackOverflow.XAML"
x:Class="StackOverflow.XAML.Layout"
Background="{DynamicResource Layout.Background}"
AllowsTransparency="True"/>
Project File Structure:
XAML
Layout.xaml
Theme
Dark.xaml
App.xaml
Other information:
Solution Configuration: Debug
Solution Platform: x64
Microsoft Visual Studio Community 2019 v16.7.3
Update:
For some reason the problem reappeared with the Application StartUpUri, if you noticed that I didn't use this attribute because I have to verify the user's login before giving them access to the main window. So behind the code in App.xaml.cs I call Login.ShowDialog() and Layout.ShowDialog(). After setting this attribute to Layout Window, I can notice that the application is consuming the resources defined under Dark.cs, so if I change this line:
<SolidColorBrush x:Key="Layout.Background">​​Lime</SolidColorBrush>
The layout background changed at runtime to the color Lime, but I'm wondering if it is possible to use the same resources defined in App.xaml in all project windows, in my case StartUpUri will be Login.xaml, and under Login if the user info is correct I can prevent this window from showing and show my layout window. but the question here is whether this resource named "Layout.Background" can be used in both windows?
I got the idea that the app resource dictionary defined in App.xaml is like a super global resource, which I can use whenever I want. Is it correct? because this result does not seem to support it.

MVVM - The name does not exist in the name space

I am trying to start a MVVM pattern and I have this structure:
App.xaml:
<Application x:Class="StereoVisionApp.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:StereoVisionApp"
StartupUri="MainView.xaml">
<Application.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary>
<local:MainViewModel x:Key="StereoVisionApp.MainViewModel"/>
</ResourceDictionary>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Application.Resources>
</Application>
MainViewModel.cs:
namespace StereoVisionApp.ViewModels
{
class MainViewModel
{
public MainViewModel()
{
}
}
}
I have an error on this line:
<local:MainViewModel x:Key="StereoVisionApp.MainViewModel"/>
Says:
The name "MainViewModel" does not exist in the namespace
"clr-namespace:StereoVisionApp". StereoVisionApp C:\Users\Me\source\repos\StereoVisionApp\StereoVisionApp\App.xaml
I have tried restarting million times. any help?

In Visual Studio, when you create a new folder in the project at creates a new namespace named projectname.foldername by default. (in your case: StereoVisionApp.ViewModels). All the files inside it automatically takes that namespace.
You can either:
Change the namespace in MainViewModel.cs
or
Add the new namespace to App.xaml like this:
add this in Application header in App.xaml
xmlns:vm="clr-namespace:StereoVisionApp.ViewModels"
Then use it like this:
<vm:MainViewModel x:Key="StereoVisionApp.MainViewModel"/>
Also note that the x:Key value is a string of your choice (doesn't have to be an exact location, so you can actually write:
<vm:MainViewModel x:Key="mainViewModel"/>
The x:Key value is for future reference only.

Implementing own ViewModelLocator

I wanted to implement ViewModelLocator by my own. So I implemented the simplest app in the world. I did everything as in this tutorial. But I'm still getting an exception:
XamlParseException occured
Exception thrown: 'System.Windows.Markup.XamlParseException' in
PresentationFramework.dll
Additional information: 'Provide value on
'System.Windows.StaticResourceExtension' threw an exception.' Line
number '8' and line position '9'.
This is this line:
DataContext="{Binding MainWindowViewModel, Source={StaticResource ViewModelLocator}}">
Here is the code:
App.xaml
<Application x:Class="ViewModelLocatorDemo.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:viewModelLocatorDemo="clr-namespace:ViewModelLocatorDemo">
<Application.Resources>
<viewModelLocatorDemo:ViewModelLocator x:Key="ViewModelLocator"/>
</Application.Resources>
</Application>
App.xaml.cs
namespace ViewModelLocatorDemo
{
using System.Windows;
using ViewModelLocatorDemo.Views;
public partial class App : Application
{
protected override void OnStartup(StartupEventArgs e)
{
base.OnStartup(e);
MainWindow mainWindow = new MainWindow();
mainWindow.Show();
}
}
}
ViewModelLocator.cs
namespace ViewModelLocatorDemo
{
using ViewModels;
public class ViewModelLocator
{
public MainWindowViewModel MainWindowViewModel
{
get { return new MainWindowViewModel(); }
}
}
}
MainWindow.xaml
<Window x:Class="ViewModelLocatorDemo.Views.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="300" Width="300"
DataContext="{Binding MainWindowViewModel, Source={StaticResource ViewModelLocator}}">
<Grid>
<Frame x:Name="MainFrame" Margin="50" BorderThickness="2" BorderBrush="Black" />
</Grid>
</Window>
MainWindowViewModel.cs
namespace ViewModelLocatorDemo.ViewModels
{
public class MainWindowViewModel
{
public string MainText { get; set; }
public MainWindowViewModel()
{
MainText = "The first page";
}
}
}
In this answer I found:
Make sure that the resources are defined before the usage (in Xaml
parsing order). The easiest way is to place it into App.xaml
So I have it in App.xaml. If somebody would me explain what's going on here? Why am I getting this error?

You are running into this bug WPF - App.xaml file does not get parsed if my app does not set a StartupUri?
From that page:
There's a VS code generation bug where the code necessary to connect to the rest of the program sometimes is not inserted when contains only one entry and does not have a StartupUri attribute.
From that page, there are 3 solutions (summarizing here for completeness):
Add x:Name="App"
Add more resources in App.xaml like <viewModelLocatorDemo:ViewModelLocator x:Key="ViewModelLocator"/> and <viewModelLocatorDemo:ViewModelLocator x:Key="ViewModelLocator2"/>
Rather than overriding OnStartup, try using an event instead, Startup="Application_Startup"
This was definitely not obvious, and was difficult to troubleshoot and even find an answer for in my own search. Hopefully this answer will help others find the other answer.

How to move App.xaml and not to break designer?

I have WPF project and some resources defined in App.xaml that are used in other files. When I try to move App.xaml to subdirectory designer is no longer able to find those resources. My project still compiles since I use 'Startup' event instead of 'StartupUri'. How to tell the designer where to search for resources? How it knows where they are when App.xaml is in root of project?
Update:
Project files:
App.xaml:
<Application x:Class="WpfApplication1.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Startup="startup">
<Application.Resources>
<SolidColorBrush Color="LightGray" x:Key="brush" />
</Application.Resources>
</Application>
App.xaml.cs
namespace WpfApplication1
{
public partial class App : System.Windows.Application
{
private void startup(object sender, System.Windows.StartupEventArgs e)
{
new MainWindow().Show();
}
}
}
MainWindow.xaml:
<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Height="300" Width="300" Background="{StaticResource brush}" />
MainWindow.xaml.cs
namespace WpfApplication1
{
public partial class MainWindow : System.Windows.Window
{
public MainWindow()
{
InitializeComponent();
}
}
}
Update 2:
Uploaded zipped solution to http://zalil.ru/30771604 (download will start automatically)
Mirror: http://www.speedyshare.com/files/27697250/WpfApplication1.zip

1. Move you App.xaml to your desired location
2. Refactor you App.xaml.cs namespace to accommodate the new change:
3. Rebuild your solution.
[4]. Go to your project properies and set the Startup object to your App.xaml file at the new location.
[5]. Run your application and it should work successfully :)

I can't duplicate the problem on my end. Here's what I tried:
I created a application with a style in the resources of App.xaml. I moved App.xaml to a subdirectory. I have another window that uses the style defined in the resources of App.xaml (he resides in a different directory) and it was able to resolve it just fine. I added ..\ to the beginning of my original StartupUri.
I did some searching, what version of Visual Studio are you using? Apparently there may be an bug related to your problem in VS2008:
http://bengribaudo.com/blog/2010/08/19/106/bug-single-application-resources-entry-ignored
He says a workaround for this bug is to set the x:Name attribute on Application. Hope that helps!
EDIT: I also tried handling the Startup event instead of using the StartupUri and it still worked fine.
public partial class App : Application
{
private void Application_Startup(object sender, StartupEventArgs e)
{
new MainWindow().Show();
}
}
EDIT PART 2:
Okay, I enclosed the SolidColorBrush inside a ResourceDictionary as such:
<ResourceDictionary>
<SolidColorBrush Color="LightGray" x:Key="brush" />
</ResourceDictionary>
And the window picks up the brush. The designer doesn't like it, but when I change from StaticResource to DynamicResource it stops complaining.
EDIT 3:
I just thought of something. Do you have VS2010 SP1 installed? It fixed some bugs with the designer.
And sorry, my edit number 2 didn't work as expected. I noticed my blue squiggles were gone in the xaml, but I didn't check the designer. x__x

Adding .cs in a ResourceDictionary?

I have DataTemplate in a ressource dictionnary, and in some, I need button and i don't know how i can use code behind for manage events.
I tried to put a class in my resource dictionnary like that :
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
x:Class="SLProject.Templates"
x:Class="TVTemplate">
And I definied the class in the cs file like that :
namespace SLProject.Templates
{
partial class TVTemplate
{
}
}
The build is OK but when the application started, I obtains XAML error following :
AG_E_PARSER_BAD_TYPE
I tried all I know like change the class kind to a ClassModifier, make the class to an inherited class of RessourceDictionnary ... no way.
Someone have an idee ...
Thanks.

Using the x:Class attribute allows you to define a codebehind for a ResourceDictionary.
You must specify the complete namespace of the class (i.e. x:Class="WpfApplication.MyClass"), and such class has to be defined as partial (at least VS 2010 complains and does not compile without such modifier).
I mocked-up a simple example:
1. Create a new WPF application project (WpfApplication)
2. Add a new class file (TestClass.cs) and paste the following code
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Input;
using System.Windows;
namespace WpfApplication
{
public partial class TestClass
{
private void OnDoubleClick(object obj, MouseButtonEventArgs args)
{
MessageBox.Show("Double clicked!");
}
}
}
3. Add a new ResourceDictionary (Resources.xaml), open the file and paste the following code
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
x:Class="WpfApplication.TestClass">
<Style TargetType="{x:Type Label}">
<EventSetter Event="Label.MouseDoubleClick" Handler="OnDoubleClick"/>
</Style>
</ResourceDictionary>
4. Finally, open the MainWindow.xaml and past the following code
<Window x:Class="WpfApplication.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<ResourceDictionary Source="Resources.xaml"/>
</Window.Resources>
<Grid>
<Label Content="Double click here..." HorizontalContentAlignment="Center" VerticalContentAlignment="Center" Background="Red"/>
</Grid>
</Window>
In the example I wire-up a double-click event from a Style, since it is a scenario requiring you to call some code from a ResourceDictionary.

You have the x:Class attribute defined twice, which is why you're getting the parser error. Change your declaration to this and it should work:
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
x:Class="SLProject.Templates.TVTemplate">

I Checked, and it's just an error of copy-past. I have well the class definied one time.

Best thing would be to make your own usercontrol and add your events in it . and later put this entire usercontrol in resource dictionary.