Packaged .Net Core app that uses XAML Host not building? It's a known issue - here's how to fix it.

Originally published:

The XAML Host is a powerful control that allows you to easily use UWP and WinUI 2 controls in a non-UWP application using the XAML Islands feature introduced in Windows 10 1903. Many Microsoft applications use XAML Islands, such as Notepad, Paint, Windows Terminal, the Windows Taskbar, Magnifier, File Explorer and more. Many of our applications using XAML Islands as well such as Codly, LaserCursor, KeepOn, QPad and more. The advantage of XAML Islands, is that you can use modern controls in a non-UWP application, allowing for various things such as better touch support and dark mode support. The XAML Host control makes using XAML Islands in .Net Core and .Net Framework applications easy. Unfortunately, there's an issue with newer versions of Visual Studio 2019 and all versions of Visual Studio 2022 that can prevent packaged applications that use the XAML Host not to build.

About the issue

If you follow Microsoft's documentation for a packaged app in 'Use XAML Islands to host a UWP XAML control in a C# WPF app' or do something similar in Visual Studio 2022 or a newer version of Visual Studio 2019, you might find that it doesn't build. You may receive error messages about duplicates such as the following:

• Validation error. error 80080204: App manifest validation error: Line 217, Column 27, Reason: The field "[local-name()='Extensions']/[local-name()='Extension']/[local-name()='InProcessServer']/[local-name()='ActivatableClass']" with value "Microsoft.Toolkit.Win32.UI.XamlHost.XamlApplication" must only be declared once. A duplicate exists on Line 42, Column 27.
• PRI175: 0x80073b0f - Processing Resources failed with error: Duplicate Entry.
• PRI222: 0x80073b0f - Unspecified error occurred.

Luckily, this didn't use to be an issue and doesn't occur in Visual Studio 2019 version 16.9.8 and Microsoft allows downloading older versions of Visual Studio and you can keep using the latest version of Visual Studio 2022 alongside an older version of 2019.

Downgrading Visual Studio

In order to install an older version of a specific Visual Studio product, such as Microsoft Visual Studio Community 2019, you must first uninstall the existing version of that product, if it exists. Don't worry about any other Visual Studio products installed except for the one you want to downgrade. For example, if you have Microsoft Visual Studio Community 2019 and Microsoft Visual Studio Community 2022, you don't need to uninstall Microsoft Visual Studio Community 2022 in order to downgrade to an older version of Microsoft Visual Studio Community 2019 - the two versions are independent of each other.

So basically, if you have a version of Visual Studio 2019 installed, uninstall it first before downgrading. There's no need to uninstall Visual Studio 2022 if you have it - it won't interfere so you can use the latest version of Visual Studio 2022 without any issues.

Where to download old versions of Visual Studio 2019

You can download old versions of Visual Studio 2019 here: https://learn.microsoft.com/en-us/visualstudio/releases/2019/history. Scroll down to the table under 'Release Dates and Build numbers' and find version 16.9.8 and download the appropriate version. Then run the installer to install it.

Tip: Downgrading the Community version of Visual Studio 2019? You may not see a link for it there, but you can still downgrade it. First, download the Professional version. Then run the installer you just downloaded. Once the Workloads screen appears, click the x up the top right to cancel it as shown in the following screenshot:



Once you cancel that, select the 'Available' tab:


You should be shown a screen that allows you to choose which version of Visual Studio 2019 to install. From here, just select the Community version of 2019.

After downgrading

Now that you've downgraded, open up the version of Visual Studio 2019 that you just downgraded and try and build your project again - it should now work! If you still get similar errors, you can try right clicking on the solution and select 'Clean' and once that's done, try right clicking on the solution and clicking 'Rebuild'. You can also try deleting the 'obj' and 'bin' folders in the projects you're trying to build.

Help get this fixed

Unfortunately, this issue still hasn't been fixed. You can help bring attention to Microsoft about this issue as well as discuss it with other users in the various places it has been reported. See the following links for places where this issue has been reported:


Did you have this issue? Did this article help you? Did you follow the steps in this article but still have the issue? Do you have any other workarounds for this issue? Let us know in the comments!
Tags:

Comments

Post a Comment

Popular posts from this blog

How to show placeholder text in a WPF TextBox in C# and VB

Originally published:
Image
Sometimes, when you have a text box in a user interface, you may want to add placeholder text to that text box to give users a prompt as to what to enter into the text box. If you've ever used UWP or WinUI, you'll probably have noticed that the default text box elements provide a PlaceholderText property that provides this functionality. However, WPF and Windows Forms don't provide this functionality by default. Luckily, thanks to WPF's rendering capabilities, it is quite easy to set up placeholder text manually. If you're using Windows Forms, you can make use of the ElementHost to use a WPF TextBox. Typically, placeholder text is a slightly faded colour compared to user-entered text to help distinguish it and only shows when no text is entered into the text box. An example is below: How to show placeholder text in a WPF TextBox To show placeholder text in a WPF textbox, all we need to do is show a partially transparent, intangible Label above the TextBox like so (Y
Read more

How to enable dark title bar in WPF and Windows Forms/WinForms apps in C# and VB

Originally published:
Image
Windows has had a dark mode feature for a long time now, however, as a Windows Forms and/or WPF (Windows Presentation Foundation) developer, you may have noticed that the Windows dark mode does not affect your app at all automatically - in fact the Windows dark mode only automatically affects UWP, WinUI and Chromium based user interfaces - there's no support for Windows dark mode in Windows Forms and WPF. Tip: If you want to set the title bar's colours to any colours you want instead of just light or dark, follow this guide here . Luckily, it is very easy to determine if dark mode is currently enabled and be notified any time dark mode is switched on or off - from there it's just a matter of updating your UI to match which mode Windows is in. While this may work fine for the client area of your app (i.e. the area of your app that does not include the title bar and border), you don't have a lot of control over the non-client area of your app and you'll notice that by
Read more

How to use modern icons in XAML in WPF on Windows 10 and 11

Originally published:
Image
Icons and symbols are a common part of modern user interfaces. Depending on your skills, creating your own icons may not be easy. Luckily, Windows 10 and 11 come preinstalled with plenty of icons that can be used in applications. If you've developed for UWP or WinUI and have used the SymbolIcon , you may have seen these icons before. By using these modern icons, you can create user interfaces that look consistent with the operating system. And the great part is that it's easy to use these icons with WPF (Windows Presentation Foundation) while supporting both Windows 10 and 11. 6 WPF buttons with modern icons in Windows 11 The same 6 WPF buttons with modern icons in Windows 10 Where the icons are stored These modern icons that Windows 10 and 11 include come in the form of fonts - specifically Segoe MDL2 Assets and Segoe Fluent Icons . Segoe MDL2 Assets is included in Windows 10 and 11 and Segoe Fluent Icons is included in Windows 11. Segoe Fluent Icons includes newer version
Read more

How to change the colour of a WPF or Windows Forms/WinForms title bar in Windows 11 in C# and VB

Originally published:
Image
The windows title bar has gone through various changes throughout the years - from the old title bars with user customisable colours to the newer title bars with visual styling support introduced in Windows XP to the DWM (Desktop Window Manager) rendered title bars introduced in Windows Vista. One thing about these changes is that they often explored the concepts the relationship of the title bar to the client area of Windows and who is in control of what the title bar looks like. For example, in Windows XP, the user could only choose between specific title bar styles unless you used the Windows classic theme, in which case you could choose your own title bar colours or even use gradients if you wanted. With the addition of the DWM in Windows Vista, Microsoft explored the idea of extending the title bar into the non client area of Windows - think File Explorer and Microsoft Word for example. Where we are now In modern versions of Windows, the title bar only uses the DWM version and all
Read more

Microsoft WebView2: How to check if the WebView2 runtime is installed in C# and VB

Originally published:
With the initial release of Windows 10, Microsoft released a completely new web browser - Microsoft Edge - that used its own rendering engine - EdgeHTML. In recent years, Microsoft deprecated the original version of Microsoft Edge and replaced it with a Chromium based version. The original version of Microsoft Edge came with a control called WebView which could be used by apps to display content. Now that Microsoft has released the new Chromium based Edge, a new control has been released called WebView2. The existing WebView control still uses the original Microsoft Edge whereas the new WebView2  uses the Chromium based Microsoft Edge. The new control however, is not reliant on the same version of Microsoft Edge that is used as the main browser - instead it is reliant on a separate component known as the WebView2 Runtime (except in the case of non-stable channels, which come with the WebView2 runtime). This component is preinstalled in Windows 11 and is currently being rolled out to W
Read more