.NET Core Window not showing correct content

I did a simple test. In my MainWindow.xaml.cs I did this test,

public MainWindow()

{

   var aboutWindow = new About();

    aboutWindow.ShowDialog()

}

When I ran this test the aboutWindow shows but it still has the same issue the "aboutWindow" is shown but it's blank showing no content. Would it be possible to zip up my solution and provide it for evaluation

Thank you for performing that additional test and for confirming the result. Based on your observation that the about window opens but it still appears blank even when created directly from the MainWindow constructor. It seemed the issue lies in how the XAML for about.xaml is being compiled or loaded at runtime.

Let's go through the possible causes and recommended next steps.

Root cause analysis:

When a WPF window appears but display no content, it generally indicates one of the following:

1.      The About.xaml file is not compiled as WPF page resource.

• This can happen if the files build action is incorrect.

2.      The name is page or class linkage between About.xaml and About.xaml.cs is mismatched.

• If the x: Class in XAML doesn't match the code behind class declaration, WPF cannot locate or load the content.

3.      Resource or layout initialization failed silently.

• If InitializeComponent() is missing or commented out in About.xaml.cs, the XAML UI is never rendered.

Recommended steps:

please verify the following items:

1.      Check Build Action

• In solution explorer, right-click About.xaml-> properties Ensure:                

    Build Action:Page
    Custom Tool: MSBuild:Compile
  

  If it's set to resource or none, WPF won’t compile the XAML markup properly.

2.     Verify Class and Namespace

• Open About.xaml and ensure the x: Class matches exactly with your code-behind file.

Make sure the namespace and class name are consistent between XAML and code-behind.

3.     Confirm InitializeComponent() exists

In about.xaml.cs, ensure that InitializeComponent() is being called in the constructor:

Public About()
{
   InitializeComponent()
}              
                                
                

Without this line, the compiled XAML content will not be loaded.
4.      Clean and Rebuild

Sometimes stale compiled XAML can cause this issue. Perform a full rebuild:

• close Visual Studio.
• Delete the bin and obj folders.
• Reopen the project.
• Choose build> clean solution, then build> rebuild solution.

5.      Verify startup Uri and application definition

Check your App.xaml to ensure there are no duplicates StartupUri or multiple MainWindow initialization that could interfere with XAML resource loading.

Once these steps are applied, the above window should correctly render its defined UI content.

Please let us know if you require any further assistance we’re happy to help. If you found this information useful, kindly mark this as "Accept Answer".

This is my MainWindow.xaml

"<Window x:Class="MdxCmp.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"

    xmlns:local="clr-namespace:MdxCmp"

    xmlns:VIEW_MODEL="clr-namespace:MdxCmp.VIEW_MODEL"

    mc:Ignorable="d"

    Title="MainWindow" Height="450" Width="926"  ResizeMode="CanMinimize" >

<Window.Resources>

    <VIEW_MODEL:ViewModelAdditionalInfo x:Key="AdditionalInfoVM"/>

    <!-- Style for submenu items to have black background and white foreground -->

    <Style TargetType="MenuItem" x:Key="SubMenuItemStyle">

        <Style.Triggers>

            <Trigger Property="Role" Value="SubmenuItem">

                <Setter Property="Background" Value="Black"/>

                <Setter Property="Foreground" Value="White"/>

            </Trigger>

        </Style.Triggers>

    </Style>

</Window.Resources>

<Grid>

    <Grid.RowDefinitions>

        <RowDefinition Height="Auto"/>

        <!-- For MainMenuTextBox -->

        <RowDefinition Height="*"/>

        <!-- For main content -->

    </Grid.RowDefinitions>

    <Grid.ColumnDefinitions>

        <ColumnDefinition Width="250"/>

        <ColumnDefinition Width="*"/>

    </Grid.ColumnDefinitions>

    <StackPanel Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="2"

        Background="#2D2D30"

        VerticalAlignment="Stretch"

        DataContext="{StaticResource AdditionalInfoVM}">

        <Menu Background="#2D2D30" Foreground="White" FontSize="16">

            <MenuItem Header="Additional Info">

                <MenuItem Header="UserGuide" Command="{Binding UserGuideCommand}" Style="{StaticResource SubMenuItemStyle}"/>

                <MenuItem Header="About" Command="{Binding AboutCommand}" Style="{StaticResource SubMenuItemStyle}"/>

            </MenuItem>

        </Menu>

    </StackPanel>

    <!-- Left Menu Bar -->

    <StackPanel Grid.Row="1" Grid.Column="0" Background="#2D2D30" VerticalAlignment="Stretch">

        <!-- Spacer: 5 lines ≈ 80px -->

        <Border Height="80" Background="Transparent"/>

        <!-- Selection Tree with Root Node "MDX" -->

        <TreeView Margin="10,10,10,10" Background="#2D2D30" BorderThickness="0">

            <TreeViewItem Header="MDX" x:Name="MdxRootTreeViewItem" Foreground="Green">

                <StackPanel Orientation="Horizontal" Width="126">

                    <CheckBox Content="Mdx Security Level Compare"

                    IsChecked="{Binding IsMdxSecurityLevelCompareChecked,Mode=TwoWay}"

                    Foreground="Green"/>

                </StackPanel>

                <StackPanel Orientation="Horizontal">

                    <CheckBox Content="Mdx Function 2"

                    IsChecked="{Binding IsMdxFunction2Checked, Mode=TwoWay}"

                    Foreground="White"/>

                </StackPanel>

                <StackPanel Orientation="Horizontal">

                    <CheckBox Content="Mdx Function 3"

                    IsChecked="{Binding IsMdxFunction3Checked, Mode=TwoWay}"

                    Foreground="White"/>

                </StackPanel>

                <StackPanel Orientation="Horizontal">

                    <TreeViewItem Header="DIDs" x:Name="DidsRootTreeViewItem" Foreground="Green">

                        <StackPanel Orientation="Horizontal">

                            <CheckBox Content="DID Sub Function"

                            IsChecked="{Binding DidSubFunctionMdxFunction2Checked, Mode=TwoWay}"

                            Foreground="White"/>

                        </StackPanel>

                    </TreeViewItem>

                </StackPanel>

            </TreeViewItem>

        </TreeView>

    </StackPanel>

    <!-- Host for child pages -->

    <Frame x:Name="WindowHost"

        Grid.Column="1"

        Background="Black"

        NavigationUIVisibility="Hidden" Margin="0,23,0,0" Grid.RowSpan="2"/>

</Grid>

</Window>

"

This is my, About Window " <Window x:Class="MdxCmp.VIEW.AboutPage"

    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 

    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 

    xmlns:local="clr-namespace:MdxCmp.VIEW"

    mc:Ignorable="d" 

    Title="About"

    Height="600"

    Width="600">

<Grid Background="Black">

    <Grid.RowDefinitions>

        <RowDefinition Height="Auto"/>

        <RowDefinition Height="*"/>

    </Grid.RowDefinitions>

    <Image Grid.Row="0"

           Source="MdxFordLogo.bmp"

           HorizontalAlignment="Center"

           VerticalAlignment="Center"

           Width="243"

           Height="100"

           Stretch="Uniform"/>

    <TextBlock Grid.Row="1"

               Text="About Page Loaded"

               Foreground="Red"

               FontSize="24"

               HorizontalAlignment="Center"

               VerticalAlignment="Top"/>

</Grid>

</Window>"

This is my Main.Window.xaml.cs "using MdxCmp.MODEL;

using MdxCmp.VIEW;

using MdxCmp.VIEW_MODEL;

using System.Reflection;

using System.Text;

using System.Windows;

using System.Windows.Controls;

using System.Windows.Data;

using System.Windows.Documents;

using System.Windows.Input;

using System.Windows.Media;

using System.Windows.Media.Imaging;

using System.Windows.Navigation;

using System.Windows.Shapes;

namespace MdxCmp

{

/// <summary>

public partial class MainWindow : Window

{

    private ViewModelSecurityLevelComp _sharedViewModel = new ViewModelSecurityLevelComp();

    private Workflow MDXGuiTileBarInfo;

    public MainWindow()

    {

        InitializeComponent();

        this.DataContext = _sharedViewModel;

        // SetMenuSelection(BtnMdxSecurityLevelCompare);

        WindowHost.Navigate(new MdxSecurityLevelComparePage(_sharedViewModel));

        // Set Assembly Version in the TextBlock

        var version = Assembly.GetExecutingAssembly().GetName().Version;

        var versionString = $"{version.Major}.{version.Minor}.{version.Build}";

        // This is the Title Bar Info that will have

        // 1) The MdxCmp Assembly Version

        // 2) A string denoting DEV, STAGE, PROD or Local Build based on the build pipeline used.

        // 3) The Git Build Number and Build Date if applicable.

        MDXGuiTileBarInfo = new Workflow(versionString);

        MDXGuiTileBarInfo.GetMDXValidatorVersion();

        this.Title = "Mdx Compare Tool   " + MDXGuiTileBarInfo.GetMDXValidatorVersion();

        var AboutWindow = new AboutPage();

        AboutWindow.Show();

    }



}"

In file MainWindow.xaml.cs, near the end of the MainWindow() constructor, there's a call to show the About page (in the code it's the AboutWindow.Show() ) this call launches a blank page. It should launch a Window with described content in file About.xaml.cs Below is a screenshot showing the properties of About.xaml The settings are per what you instructed me to set them at. Is there anything obvious as to what I'm doing wrong?

Thank you for providing the additional screenshots and details. This level of information is extremely helpful for diagnosing the issue!

I have thoroughly reviewed the XAML, the C# Constructor, and the file properties you provided. Based on the fact that the window is blank even when launched directly from the main window constructor, and your property settings, I have identified the root cause of blank window.

The primary issue is a mismatch in the root element of your About.xaml and the build action you have applied.

1.      Your XAML indicates it's a window:

• the file About.xaml begins with : Window x:Class="MdxCmp.VIEW.AboutPage"
• the corresponding code-behind should inherit from Windows

2.      Your build action is set incorrectly:

• the screenshot shows you have set the build action for About.xaml to Page.

In WPF, when the root element is <Window>, the build action must be applicationDefinition or implicitly page if using the standard structure, but setting it to just page when the class inherits from window can sometimes prevent the XAML compilation from generating the correct BAML (binary application markup language) necessary for loading the window content at runtime.

Solution and action plan

the recommended fix is to ensure consistency between the class definition and the file properties.

**1.      **Fix the build action(recommended)

since your XAML is defined as a window and you are instantiating it with new AboutPage(),Show(), the compiler needs to process it as a window resource.

• In solution explorer, right click About.xaml.
• Select properties.
• Change the build action from page to resource.

Setting a window to resource ensures the XAML is compiled into the assembly without attempting to process it as a navigation style page. While page works for Windows in many cases, switching to resource is a robust solution for standalone window classes, especially when facing compilation/loading issues like this.

**2.      **Confirm static content  

The About.xaml snippet that you have defined static content which should be visible

<Grid Background=”Blank”>
	<Grid.RowDefinitions>….</Grid.RowDefinitions>
	<Image Source= “MdxFordLogo.bmp” Grid.Row=”0” …./>
	 <TextBlock Grid.Row=”1” Text=”About Page Loaded” Foreground=”Read”…./>
</Grid>

The simple text block with the text “about page loaded” should absolutely appear if the XAML it's compiled and loaded correctly. If changing the build action to resource works, this text will be the confirmation.

**3.      **Clean and rebuild (crucial final step)

after making any change to a build action, you must perform a full reset to ensure the compiler generates the correct output files.

• Close Visual Studio
• manually delete the bin and obj folder from your project directory.
• Reopen the project.
• Go to build> clean solution.
• Go to build> rebuild solution.

After completing these steps, the above window should open and correctly display the content defined in About.xaml.

Please let us know if you require any further assistance we’re happy to help. If you found this information useful, kindly mark this as "Accept Answer".

Thanks for the response. I followed your instructions. Per the attached picture,

I set the Build Action (About.xaml) to Resource. I now have a new error. When I try to do this " Application.Current.Dispatcher.Invoke(() =>

{

 AboutPage aboutWindow = new AboutPage();


 

 //  aboutWindow.Title = "About";

 // aboutWindow.Width = 600;

 // aboutWindow.Height = 600;

 // aboutWindow.Background = System.Windows.Media.Brushes.Black;

 // aboutWindow.WindowStartupLocation = WindowStartupLocation.CenterScreen;

 aboutWindow.Owner = Application.Current.MainWindow;

 aboutWindow.ShowDialog();
``` });" VS_2022 gives an error for the code "  AboutPage aboutWindow = new AboutPage();" The type or namespace name 'AboutPage' cannot be found (are you missing a using directive or an assembly reference?" I don't know how to resolve this error.  Do I need to add something to the MainWindow.xaml, <Window.Resources></WIndow.Resources> section? or do I need to define a <Window.Rescourse></Window.Resources> section in in my About.xaml file?

I am very glad to hear that you are able to see the AboutPage now.

The core issue, as we suspected, lay in the project file linkage (.csproj), when you manually fixed the <ItemGroup> entries, you ensured the C# compiler and the XAML compiler correctly understood their dependency, allowing the necessary partial class definitions to be generated.

Here is the answer to your final questions:

Why the manual Fix was necessary:

The issue of Visual Studio not correctly generating or maintaining <ItemGroup> entries is rare, but it usually points to a specific sequence of actions you may have taken.

1. Inconsistent file operations The WPF compiler relies on the DependentUpon tag to connect XAML and C# files. VS is designed to manage this automatically, but it can fail if:
   1. Files were Moved/Renamed Manually: if you used Windows Explorer (instead of solution explorer) to move About.xaml or About.xaml.cs into the VIEW folder, VS wouldn't update the project file correctly.
   2. Initial Creating errors: The XAML file was created outside of the standard "Add New Item -> Window (WPF)" template, or the C# code-behind file was added separately later.
   3. Conflicting file reference: in very large or old projects, other build targets or tooling can sometimes interfere with the standard WPF project file structure.

Will This happen with new Windows?

you should not have this issue when adding new windows in the future, provided you use the correct method.

1. In solution explorer, right.click the desired folder (e.g., VIEW0.
2. Select Add -> Windows (WPF)...
3. give it a name (e.g., NewWindow.xaml) and click Add.

When you use the standard VS template for adding a new WPF window, it automatically:

• Creates NewWindow.xaml and NewWindow.xaml.cs
• adds the correct x:Class attribute to XAML.
• Adds the correct namespace and public partial class to the C# files.
• Most importantly, it generates the perfectly linked <page> and <Compile> entries in your project file, which prevents the blank window and "class not found" errors.

If you stick to using VS templates for adding new UI components, you can be confident the linkage issue won't reappear

Please let us know if you require any further assistance we’re happy to help. If you found this information useful, kindly mark this as "Accept Answer".