Navigation to a Blank Page in Class library project leads to Exception in UWP

[syncsiva]

Describe the bug
Navigation to a Blank Page in Class library project leads to Exception

Steps to reproduce the bug
ReunionBlackAppUWP.zip

Steps to reproduce the behavior:

1. Just open the sample and run, you will get xaml parse exception
   Exception thrown: 'Windows.UI.Xaml.Markup.XamlParseException' in ClassLibrary1.dll
   An exception of type 'Windows.UI.Xaml.Markup.XamlParseException' occurred in ClassLibrary1.dll but was not handled in user code
   XAML parsing failed.
2. Its just a blank app and a class library with blank winui page.

Expected behavior
Should work without any exception. It works fine with WinUI3 Preview4 and facing exception only after updating to Project reunion.

Screenshots

Version Info
Microsoft.ProjectReunion -> Version="0.5.0-prerelease
Visual Studio : VS 2019 16.10 Preview 1.0
Microsoft Windows Version 20H2 (OS build 19042.867)

Additional context
It works fine with WinUI3 Preview4 and facing exception only after updating to Project. Any workaround is very helpful.

[mrlacey]

@syncsiva In your example, you've added a UWP (WInUI 2) blank page to the ClassLibrary but then are trying to compile it with the WinUI 3 toolchain.
This means that the class you've defined (in BlankPage1.xaml.cs) is based on Windows.UI.Xaml.Controls.Page but the code that is generated by the compiler create a partial file that inherits from Microsoft.UI.Xaml.Controls.Page.

If you update BlankPage1.xaml.cs like this it will compile:

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using Microsoft.Foundation;
//using Windows.Foundation.Collections;
using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Controls;
using Microsoft.UI.Xaml.Controls.Primitives;
using Microsoft.UI.Xaml.Data;
using Microsoft.UI.Xaml.Input;
using Microsoft.UI.Xaml.Media;
using Microsoft.UI.Xaml.Navigation;

To avoid this in future, make sure you add a Blank Page (WinUI) to your WinUI 3 projects.

It would be really great if tooling could detect this and provide a more helpful/specific error message.

[syncsiva]

@mrlacey I have added Black Page (WinUI) only. Initially i have added BlankPage1 based on Windows.UI.Xaml.Controls.Page and later re-attached the correct the sample. Please refer below sample where exception thrown when we navigate to the page in class library project.

Sample app:
App8.zip

Screen shot:

[mrlacey]

@syncsiva Having investigated, this looks to be an issue with the code that WinUI3 generates as part of compiling the XAML files, so I have logged a bug there.

[syncsiva]

@mrlacey It was worked when i use WinUI3 Preview4 project template and not working after upgrading to Project Reunion 0.5 Preview.

[syncsiva]

Any workaround solution to the problem would be greatly appreciated!

[bpulliam]

UWP is no longer supported by WinUI 3. If you can repro the issue on current builds without UWP, please reactivate or open a new issue.

Thanks!