UWP > WINUI3 migration problem

Question

UWP > WINUI3 migration problem

BitSmithy 2,226

Hello,

I am trying to migrate my UWP based Windows Store app to WINUI3.

I had in win store UWP version.

Next, I created WINUI3 version. Validated it in my VisualStudio and published it.

WINUI3 app was validated and published via Partner Center.

Next, I updated the app on my laptop using Microsft Store function.

The app was updated sucesfully.

But now when I want to run it, It starts, but next crashes after a while.

WinUI3 App was developed on Windows 11. Packages was made in VS2022 and next in VS2026.

Laptop where I try to run the app works under Windows 10. App is published, only for direct audience (is not public.)

Event Viewer log, below:

Faulting application name: Support Center.exe, version: 1.0.0.0, time stamp: 0x68ff0000

Faulting module name: KERNELBASE.dll, version: 10.0.19041.4597, time stamp: 0x7980d421

Exception code: 0xc000027b

Fault offset: 0x000000000012d352

Faulting process ID: 0x4540

Faulting application start time: 0x01dc5d30d5e5a12f

Faulting application path: C:\Program Files\WindowsApps\20089Bitsmithy.SupportCenter_2.0.7.0_x64__dbfmhnwy1vfar\Support Center.exe

Faulting module path: C:\WINDOWS\System32\KERNELBASE.dll

Report ID: 32e39dd0-0c10-469d-adc7-5a985bddc5a8

Faulting package full name: 20089Bitsmithy.SupportCenter_2.0.7.0_x64__dbfmhnwy1vfar

Faulting package-relative application ID: App

Harry Vo (WICLOUD CORPORATION) 3,820 Reputation points Microsoft External Staff Moderator

2025-11-28T09:30:24.89+00:00

Hi @BitSmithy , do you have any response on Danny's response?
BitSmithy 2,226 Reputation points

2025-11-30T16:28:24.24+00:00

I am working on response, but this case is difficult for me and I need some time to check everything.
Harry Vo (WICLOUD CORPORATION) 3,820 Reputation points Microsoft External Staff Moderator

2025-12-01T03:05:52.6666667+00:00

Thanks for update, @BitSmithy , just take your time and let me know if you need any help !
BitSmithy 2,226 Reputation points

2025-12-07T16:59:13.8966667+00:00

I discovered a reproducible path to the error. Details in Danny's thread.

2 answers

Your answer

Harry Vo (WICLOUD CORPORATION) 3,820 Reputation points Microsoft External Staff Moderator

2025-11-28T09:30:24.89+00:00

Hi @BitSmithy , do you have any response on Danny's response?
BitSmithy 2,226 Reputation points

2025-11-30T16:28:24.24+00:00

I am working on response, but this case is difficult for me and I need some time to check everything.
Harry Vo (WICLOUD CORPORATION) 3,820 Reputation points Microsoft External Staff Moderator

2025-12-01T03:05:52.6666667+00:00

Thanks for update, @BitSmithy , just take your time and let me know if you need any help !
BitSmithy 2,226 Reputation points

2025-12-07T16:59:13.8966667+00:00

I discovered a reproducible path to the error. Details in Danny's thread.

Answer 1

It seems like you are encountering a crash with your WinUI 3 application after migrating from UWP. Here are some points to consider that might help you troubleshoot the issue:

Compatibility: Ensure that your WinUI 3 app is compatible with Windows 10. While WinUI 3 can run on Windows 10, certain features or APIs might behave differently compared to Windows 11. Make sure that you are not using any APIs or features that are exclusive to Windows 11.
Event Viewer Logs: The exception code 0xc000027b indicates a problem with the application, which could be related to an unhandled exception or a failure in the application logic. Check the Event Viewer logs for more detailed information about the crash, and consider adding error handling in your application to capture exceptions that may occur during runtime.
Testing on Windows 10: Since you developed and published the app on Windows 11, it would be beneficial to test the app on a Windows 10 environment during development to identify any issues that may arise specifically on that OS.
Debugging: Use Visual Studio to debug the application on your Windows 10 machine. This can help you identify the exact point of failure and understand why the application crashes.
Dependencies: Ensure that all dependencies required by your WinUI 3 application are properly included and compatible with Windows 10.
Known Issues: Review the limitations and known issues related to WinUI 3, especially regarding its use in desktop apps, as certain APIs may not be supported in that context.

If the problem persists, consider reaching out to the Microsoft developer community or support for more targeted assistance.

References:

Answer 2

Danny Nguyen (WICLOUD CORPORATION) 5,430 Microsoft External Staff Moderator

Hi,

From the information you’ve provided, this looks less like a random crash and more like a compatibility / packaging issue between your WinUI 3 app (Windows App SDK) and the Windows 10 device you’re running it on.

The KERNELBASE.dll crash with exception code 0xc000027b is a generic native failure that often appears when something goes wrong very early in the app’s startup, for example due to unsupported OS version or APIs.

Below are some checks and suggestions you can try.

1. Verify Windows App SDK version vs. Windows 10 build

In your WinUI 3 project, open the .csproj file and locate the Windows App SDK package reference, for example:
```
   <PackageReference Include="Microsoft.WindowsAppSDK" Version="1.5.240627000" />
```
Check the documentation / release notes for that Windows App SDK version to confirm the minimum supported Windows 10 build.
On the Windows 10 laptop:
- Press Win + R, type winver, and check the exact Windows 10 version and build number.
- Make sure this build is supported by the Windows App SDK version you are using.

If the laptop is running an older Windows 10 build than required by your Windows App SDK version, the app may install successfully from the Store but fail at runtime.

If this is the case:

Either update the Windows 10 machine to a supported build, or

Use an earlier Windows App SDK version that supports your target Windows 10 build, rebuild and republish the app.

2. Check Package.appxmanifest target device family settings

Even for a packaged WinUI 3 desktop app, the manifest defines the supported OS versions.

Open the Package.appxmanifest file (usually in the packaging project).

Find the TargetDeviceFamily element, for example:


   <TargetDeviceFamily Name="Windows.Universal"

                       MinVersion="10.0.17763.0"

                       MaxVersionTested="10.0.22621.0" />

Confirm that:
- MinVersion is less than or equal to the Windows 10 build number on your laptop.
- MaxVersionTested can be higher (e.g., a Windows 11 build), but MinVersion must not exceed the version of the target machine.

If MinVersion is set higher than the Windows 10 build where you’re installing the app, it can lead to unexpected runtime failures.

3. Capture the managed exception details from Event Viewer

The log you posted is the native Application Error event. For .NET / WinUI applications, there is usually a corresponding .NET Runtime event that contains more useful information.

On the Windows 10 laptop:

Open Event Viewer.
Navigate to Windows Logs → Application.
Look for:
- Entries with Source = .NET Runtime, close in time to the crash you reported.
Open that event and check for:
- Exception type (for example, System.TypeLoadException, System.DllNotFoundException, etc.),
- Exception message,
- Stack trace.

These details often identify the specific API or assembly that is failing. If you can provide this information, it will be much easier to determine whether the issue is due to an unsupported API on Windows 10 or another migration problem.

4. Review UWP-specific or OS-specific APIs used after migration

When migrating from UWP to WinUI 3 desktop, it’s possible that some UWP-specific APIs remain in the code. These can cause problems when running as a desktop app, especially on older OS versions.

Please review your code (especially app startup code such as App constructor, OnLaunched, and the first page’s constructor / Loaded handler) for:

UWP namespaces such as Windows.UI.Xaml.*.
UWP-only APIs, e.g.:
- Windows.UI.Core.CoreWindow,
- Windows.UI.ViewManagement.ApplicationView,
- Some members of Windows.ApplicationModel.* and Windows.System.* that assume a UWP container.
Any APIs introduced in Windows 11 that might not exist or behave the same on the Windows 10 build you are targeting.

If one of these APIs is invoked during startup and is not available on the Windows 10 device, it can cause the app to terminate with a native exception.

5. Confirm project type and migration approach

Please also confirm that:

The project is created from a WinUI 3 (Windows App SDK) desktop app template (for example, “Blank App, Packaged (WinUI in Desktop)” in Visual Studio).
You are not using the original UWP project type with partial WinUI 3 references.

If you migrated by directly modifying the existing UWP project, a more reliable approach is:

Create a new WinUI 3 desktop (packaged) project in Visual Studio.
Move your XAML, ViewModels, and business logic into this new project.
Reconfigure capabilities and manifest settings as needed.
Check the Windows App SDK version and TargetDeviceFamily as described above.
Build, deploy, and test on both Windows 11 and the target Windows 10 device.

To further investigate, it would be helpful if you could provide:

The Windows 10 version and build number from the affected machine (winver dialog).
The Windows App SDK package reference (name and version) from your .csproj.
The TargetDeviceFamily element from your Package.appxmanifest.
The .NET Runtime event details from Event Viewer (exception type, message, and the first part of the stack trace).

Hope this helps

Danny Nguyen (WICLOUD CORPORATION) 5,430 Reputation points Microsoft External Staff Moderator

2025-11-28T10:53:02.9766667+00:00

Hi, just checking in. Did my answer help with your problem? Feel free to reach out if you need any help. Also please consider accepting if it works for you. Thank you
BitSmithy 2,226 Reputation points

2025-11-30T17:28:42.8566667+00:00
Partly answer:

During migration, I created a completely new project in WinUI 3 using VS2022 on a Windows 10 laptop. Then I manually copied all the XAML and C# code from the old UWP project. After adjusting the XAML and C#, everything was working well. Next, I moved my WinUI 3 package to the Windows 11 laptop using a USB drive (not a repository). I ran it there, and it worked fine. Then I published it using VS2022 and later using VS2026. Publishing and installation on the Windows 10 laptop were successful, but running the app failed, so I posted this issue. Afterwards, I moved my code back to the Windows 10 laptop using the USB drive and ran it (F5) in VS2022. Running in both Debug and Release modes was successful. So I believe that all APIs are attached, but I will check the points mentioned in your answer and post the verification results.

You wrote: If the laptop is running an older Windows 10 build than required by your Windows App SDK version, the app may install successfully from the Store but fail at runtime.

It is very wrong info, because developer cant controll which Windows version their customers (Windows users) have . If windows user has wrong Windows version the app shouldnt be installed and old package should be kept there.
Danny Nguyen (WICLOUD CORPORATION) 5,430 Reputation points Microsoft External Staff Moderator

2025-12-01T09:46:44.29+00:00

The second point is based on some cases where sometimes because of cache issues or some other reasons, Windows with builds older than specified by MinVersion can still install. These occurrences are anecdotal only but I think it's worth noting:

https://learn.microsoft.com/en-us/answers/questions/5594348/how-do-i-configure-my-appxmanifest-so-that-it-can
BitSmithy 2,226 Reputation points

2025-12-01T14:02:38.8633333+00:00
I got closer look to my problem. It looks that that Windows version doesnt matter but code optimalization matters.

I set VS run mode to release, now I have problems with code:

public sealed partial class MainWindow : Window { //initializes ocChats ObservableCollection<Chat> ocChats = new ObservableCollection<Chat>(); ... private void Page_Loaded(object sender, RoutedEventArgs e) { lvChatAppIds.ItemsSource = ocChats; //lvChatAppIds is ListView } ...

Compiler tells "Object reference not set to an instance of an object." I cant understand this problem, because of ocChats is initialized before this code.

Other, similiar problem is with code:

if (ocChats.Any()) { ocChats = new ObservableCollection<Chat>( ocChats.OrderByDescending(x => x.LastMessageDateTime) ); lvChatAppIds.ItemsSource = null; lvChatAppIds.ItemsSource = ocChats; }

This code casts exception "Object reference not set to an instance of an object." too. I cant understand this error too, because ocChats is initialized some code lines before assotiation to ItemsSorurce.

In debug mode all works well. When I was been using UWP I naver had problems when I was managing ItemsSource code behind. I could trust PageLoaded event too.

Could any one explain whats going about and how to fixmy problem. How to properly migrate Lists and ObservableCollections from UWP to WINUI3.
Danny Nguyen (WICLOUD CORPORATION) 5,430 Reputation points Microsoft External Staff Moderator

2025-12-02T06:48:34.9566667+00:00
From the snippets you posted, the exception message (“Object reference not set to an instance of an object.”) means that there are possible nulls:

ocChats i

lvChatAppIds,

You should check which object is actually null

Add a quick check in the handler:

private void Page_Loaded(object sender, RoutedEventArgs e) { if (lvChatAppIds is null) throw new InvalidOperationException("lvChatAppIds is null in Page_Loaded"); if (ocChats is null) throw new InvalidOperationException("ocChats is null in Page_Loaded"); lvChatAppIds.ItemsSource = ocChats; }

Run that build and see which line throws. In many WinUI 3 migrations, it turns out that the control (lvChatAppIds) is null because of XAML wiring/lifecycle, not the collection.

Also make sure InitializeComponent() runs before you touch controls.

BitSmithy 2,226

This isn't so simple. if any of these objects are null, an exception will be thrown in both debug and release modes.

If I use x:Bind and I have definded ListView this way:

<ListView x:Name="lvChatAppIds" Grid.Column="0"  
      ItemsSource="{x:Bind ocChats, Mode=OneWay}"

and code behind:

public sealed partial class MainWindow : Window     
{ 
	public ObservableCollection<Chat> ocChats { get; set; } = new(); // new 			ObservableCollection<Chat>(); 
...
	public MainWindow()
    {
            InitializeComponent();  
	} 
...

This code casts exception "System.NullReferenceException: „Object reference not set to an instance of an object." during app starting in MainWindow.g.cs file

MainWindow.g.cs file
public void Activated(object obj, global::Microsoft.UI.Xaml.WindowActivatedEventArgs data)
{
	this.Initialize(); <------ Exception is thrown here
}

If I use Binding with the same code behind

<ListView x:Name="lvChatAppIds" Grid.Column="0"  
	ItemsSource="{Binding ocChats, Mode=OneWay}"

This code casts exception "System.NullReferenceException: „Object reference not set to an instance of an object."

...
private void Page_Loaded(object sender, RoutedEventArgs e)
{
	 if (ocChats != null && pgRoot != null && lvChatAppIds != null && this != null)
	{
		lvChatAppIds.DataContext = this; <--this cast exception
 	} 
...

My problem i so strangle that even AI isnt able to tell something helpfull. More, in debug mode all works fine.

BitSmithy 2,226

I discovered a reproducible path to the error. Details. below.

I create a new WINUI3 project in VS (emty packet app)

I create a XAML

       <Grid>
           <Page>
               <ListView x:Name="lv" ItemsSource="{x:Bind oc, Mode=OneWay}"></ListView>
           </Page>
       </Grid>

I create the code behind

    public sealed partial class MainWindow : Window
    {
        public ObservableCollection<MyClass> oc { get; set; } = new();
        public MainWindow()
        {
            InitializeComponent();
        }
    }
    public class MyClass
    {
        public string Name { get; set; } = string.Empty;
    }

Now if I want to debug it using debug mode, app runs, but when I use release mode app crashes with exception.

Danny Nguyen (WICLOUD CORPORATION) 5,430 Reputation points Microsoft External Staff Moderator

2025-12-11T04:31:15.0433333+00:00
Hi,

Thank you for the repro path, and also sorry for the late response.

I think I managed to track this problem down to how WinUI handles trimming in Release builds. In your repro, I added the following PropertyGroup to the project file:

<PropertyGroup> <PublishTrimmed>false</PublishTrimmed> <TrimMode>partial</TrimMode> </PropertyGroup>

and then removed the conditional trimming line:

<PublishTrimmed Condition="'$(Configuration)' != 'Debug'">True</PublishTrimmed>

After doing that, the crash in Release stopped happening.

So the core issue wasn’t the ObservableCollection or the Page_Loaded event, but trimming being too aggressive for WinUI 3’s generated XAML / x:Bind code. For now, disabling or relaxing PublishTrimmed is the simplest fix when migrating UWP apps to WinUI 3, especially if you’re using x:Bind and code‑behind to manage ItemsSource.
Danny Nguyen (WICLOUD CORPORATION) 5,430 Reputation points Microsoft External Staff Moderator

2025-12-16T02:47:22.1633333+00:00

Hi, is there any update on this problem?

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UWP > WINUI3 migration problem

2 answers

Your answer