C++/CLI dll could not be loaded in WinUI3 app

Ueda Kunio(上田邦男) 20

When I called (i.e. instanciated) my class object (e.g. MyTest) which is declared as a managed class in my C++/CLI dll, I saw the following error:

System.IO.FileNotFoundException: 'Could not load file or assembly <MyTest>'

I am sure that the C++/CLI dll is located at the same directory as my app exe.

My app is WinUI3 app and uses the C++/CLI dll to use my C++ dll and has been built as unpackaged app because I thought that sandbox limitation might be related if I used packaged version but it doesn't..

Minxin Yu 10,031 Reputation points Microsoft Vendor

2024-01-10T08:03:20.27+00:00

What type of WinUI3 project are you using? Can you provide steps and minimal sample to help us reproduce your problem?
Ueda Kunio(上田邦男) 20 Reputation points

2024-01-10T09:18:04.1+00:00

Please see my next comment.
Ueda Kunio(上田邦男) 20 Reputation points

2024-01-10T09:25:19.3433333+00:00
(1) Create WinUI3 app project with using Template Studio for WInUI and add nagivation bar and an empty page

(2) Create C++/CLI library project and create a class (e.g. MyClass)

(3) In WinUI3 app project, add the reference of CLI library project

(4) Write the following code in MainPage in WinUI3 app project

public sealed partial class MainPage : Page { public MainViewModel ViewModel { get; } public MainPage() { ViewModel = App.GetService<MainViewModel>(); InitializeComponent(); // show the error, "System.IO.FileNotFoundException" MyClass obj = new MyClass(); } }
Minxin Yu 10,031 Reputation points Microsoft Vendor

2024-01-10T09:42:55.0066667+00:00

Did you set x64 target platform for winui3 project?
Ueda Kunio(上田邦男) 20 Reputation points

2024-01-10T23:24:48.57+00:00

Yes, all projects are x64.
Viorel 112.5K Reputation points

2024-01-11T08:27:43.4533333+00:00

Did you check your library using a C++/CLI Console instead of WinUI?
Ueda Kunio(上田邦男) 20 Reputation points

2024-01-12T04:29:09.2066667+00:00

@Viorel I cannot make the C++/CLI console app because of the following error shown: NETSDK1116 C++/CLI projects targeting .NET Core must be dynamic libraries. I made WPF app and refered to the CLI dll. The result also was same error.
Minxin Yu 10,031 Reputation points Microsoft Vendor

2024-01-15T02:24:19.3066667+00:00

I cannot reproduce your problem by your steps.
Create C++/CLI library project:
What kind of C++/CLI template? .NET or .NET framework and the version? How do you add references in C# projects?

1 answer

Ueda Kunio(上田邦男) 20 Reputation points

2024-04-10T23:54:42.0066667+00:00

I have resolved this issue by myself.

The cause was missing reference of some 3rd party's dll that was refered from my C++ dll and not correctly installed in my PC. (i.e. My CLI dll was no problem but C++ dll was the source of the cause, the error message was output from CLI project, though...)

I was able to pass the build by coping the missing dll to the same directory as my app exe.
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