How do you create a .NET MAUI class library and import that into your main .NET MAUI application, sucessfully?

[enjoysmath]

Steps to reproduce (in Visual Studio):

1. Create a new Class Library Project type in the same solution as your app project.
2. Add a ContentView (XAML) in a View folder under the class library project.
3. Make sure Community MVVM toolkit and anything .NET MAUI-related are up-to-date in each respective project's Nuget Package manager.
4. Right click your main project in the solution explorer and then Add > Project reference. And select your class library project. Hit Apply /Ok..

Now build everything. You'll get total catostrophe in errors.

The ones I got were these:

Output pane:

Rebuild started...
Restored C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboardGUIComponents\CEDDashboardGUIComponents.csproj (in 490 ms).
1>------ Rebuild All started: Project: CEDDashboardGUIComponents, Configuration: Release Any CPU ------
Restored C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CEDDashboard.csproj (in 1.41 sec).
1>CEDDashboardGUIComponents -> C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboardGUIComponents\bin\Release\net6.0\CEDDashboardGUIComponents.dll
1>CEDDashboardGUIComponents -> C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboardGUIComponents\bin\Release\net6.0-maccatalyst\CEDDashboardGUIComponents.dll
1>CEDDashboardGUIComponents -> C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboardGUIComponents\bin\Release\net6.0-ios\CEDDashboardGUIComponents.dll
1>CEDDashboardGUIComponents -> C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboardGUIComponents\bin\Release\net6.0-windows10.0.19041.0\CEDDashboardGUIComponents.dll
1>CEDDashboardGUIComponents -> C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboardGUIComponents\bin\Release\net6.0-android\CEDDashboardGUIComponents.dll
2>------ Rebuild All started: Project: CEDDashboard, Configuration: Release Any CPU ------
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\TimePickerTextColorTo.g.shared.cs(41,89,41,124): warning CS0436: The type 'ColorAnimationExtensions_TimePicker' in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\TimePickerTextColorTo.g.shared.cs' conflicts with the imported type 'ColorAnimationExtensions_TimePicker' in 'CEDDashboardGUIComponents, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. Using the type defined in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\TimePickerTextColorTo.g.shared.cs'.
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\SearchBarTextColorTo.g.shared.cs(41,89,41,123): warning CS0436: The type 'ColorAnimationExtensions_SearchBar' in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\SearchBarTextColorTo.g.shared.cs' conflicts with the imported type 'ColorAnimationExtensions_SearchBar' in 'CEDDashboardGUIComponents, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. Using the type defined in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\SearchBarTextColorTo.g.shared.cs'.
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\RadioButtonTextColorTo.g.shared.cs(41,89,41,125): warning CS0436: The type 'ColorAnimationExtensions_RadioButton' in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\RadioButtonTextColorTo.g.shared.cs' conflicts with the imported type 'ColorAnimationExtensions_RadioButton' in 'CEDDashboardGUIComponents, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. Using the type defined in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\RadioButtonTextColorTo.g.shared.cs'.
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\PickerTextColorTo.g.shared.cs(41,89,41,120): warning CS0436: The type 'ColorAnimationExtensions_Picker' in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\PickerTextColorTo.g.shared.cs' conflicts with the imported type 'ColorAnimationExtensions_Picker' in 'CEDDashboardGUIComponents, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. Using the type defined in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\PickerTextColorTo.g.shared.cs'.
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\LabelTextColorTo.g.shared.cs(41,89,41,119): warning CS0436: The type 'ColorAnimationExtensions_Label' in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\LabelTextColorTo.g.shared.cs' conflicts with the imported type 'ColorAnimationExtensions_Label' in 'CEDDashboardGUIComponents, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. Using the type defined in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\LabelTextColorTo.g.shared.cs'.
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\EntryTextColorTo.g.shared.cs(41,89,41,119): warning CS0436: The type 'ColorAnimationExtensions_Entry' in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\EntryTextColorTo.g.shared.cs' conflicts with the imported type 'ColorAnimationExtensions_Entry' in 'CEDDashboardGUIComponents, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. Using the type defined in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\EntryTextColorTo.g.shared.cs'.
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\ViewModel\LoginViewModel.cs(12,16,12,21): warning CS1998: This async method lacks 'await' operators and will run synchronously. Consider using the 'await' operator to await non-blocking API calls, or 'await Task.Run(...)' to do CPU-bound work on a background thread.
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\EditorTextColorTo.g.shared.cs(41,89,41,120): warning CS0436: The type 'ColorAnimationExtensions_Editor' in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\EditorTextColorTo.g.shared.cs' conflicts with the imported type 'ColorAnimationExtensions_Editor' in 'CEDDashboardGUIComponents, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. Using the type defined in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\EditorTextColorTo.g.shared.cs'.
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\DatePickerTextColorTo.g.shared.cs(41,89,41,124): warning CS0436: The type 'ColorAnimationExtensions_DatePicker' in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\DatePickerTextColorTo.g.shared.cs' conflicts with the imported type 'ColorAnimationExtensions_DatePicker' in 'CEDDashboardGUIComponents, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. Using the type defined in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\DatePickerTextColorTo.g.shared.cs'.
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\ButtonTextColorTo.g.shared.cs(41,89,41,120): warning CS0436: The type 'ColorAnimationExtensions_Button' in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\ButtonTextColorTo.g.shared.cs' conflicts with the imported type 'ColorAnimationExtensions_Button' in 'CEDDashboardGUIComponents, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. Using the type defined in 'CommunityToolkit.Maui.SourceGenerators\CommunityToolkit.Maui.SourceGenerators.Generators.TextColorToGenerator\ButtonTextColorTo.g.shared.cs'.
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CommunityToolkit.Maui.Markup.SourceGenerators\CommunityToolkit.Maui.Markup.SourceGenerators.TextAlignmentExtensionsGenerator\SearchBarTextAlignmentExtensions.g.cs(122,153,122,173): error CS0121: The call is ambiguous between the following methods or properties: 'CommunityToolkit.Maui.Markup.TextAlignmentExtensions_SearchBar.TextCenterHorizontal(Microsoft.Maui.Controls.SearchBar)' and 'CommunityToolkit.Maui.Markup.TextAlignmentExtensions_SearchBar.TextCenterHorizontal(Microsoft.Maui.Controls.SearchBar)'
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CommunityToolkit.Maui.Markup.SourceGenerators\CommunityToolkit.Maui.Markup.SourceGenerators.TextAlignmentExtensionsGenerator\PickerTextAlignmentExtensions.g.cs(122,147,122,167): error CS0121: The call is ambiguous between the following methods or properties: 'CommunityToolkit.Maui.Markup.TextAlignmentExtensions_Picker.TextCenterHorizontal(Microsoft.Maui.Controls.Picker)' and 'CommunityToolkit.Maui.Markup.TextAlignmentExtensions_Picker.TextCenterHorizontal(Microsoft.Maui.Controls.Picker)'
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CommunityToolkit.Maui.Markup.SourceGenerators\CommunityToolkit.Maui.Markup.SourceGenerators.TextAlignmentExtensionsGenerator\LabelTextAlignmentExtensions.g.cs(122,145,122,165): error CS0121: The call is ambiguous between the following methods or properties: 'CommunityToolkit.Maui.Markup.TextAlignmentExtensions_Label.TextCenterHorizontal(Microsoft.Maui.Controls.Label)' and 'CommunityToolkit.Maui.Markup.TextAlignmentExtensions_Label.TextCenterHorizontal(Microsoft.Maui.Controls.Label)'
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CommunityToolkit.Maui.Markup.SourceGenerators\CommunityToolkit.Maui.Markup.SourceGenerators.TextAlignmentExtensionsGenerator\EntryTextAlignmentExtensions.g.cs(122,145,122,165): error CS0121: The call is ambiguous between the following methods or properties: 'CommunityToolkit.Maui.Markup.TextAlignmentExtensions_Entry.TextCenterHorizontal(Microsoft.Maui.Controls.Entry)' and 'CommunityToolkit.Maui.Markup.TextAlignmentExtensions_Entry.TextCenterHorizontal(Microsoft.Maui.Controls.Entry)'
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CommunityToolkit.Maui.Markup.SourceGenerators\CommunityToolkit.Maui.Markup.SourceGenerators.TextAlignmentExtensionsGenerator\EditorTextAlignmentExtensions.g.cs(122,147,122,167): error CS0121: The call is ambiguous between the following methods or properties: 'CommunityToolkit.Maui.Markup.TextAlignmentExtensions_Editor.TextCenterHorizontal(Microsoft.Maui.Controls.Editor)' and 'CommunityToolkit.Maui.Markup.TextAlignmentExtensions_Editor.TextCenterHorizontal(Microsoft.Maui.Controls.Editor)'
2>C:\Users\fruit\OneDrive\Desktop\"[removed]"\GitHub\CEDDashboard\Source\CEDDashboard\CommunityToolkit.Maui.Markup.SourceGenerators\CommunityToolkit.Maui.Markup.SourceGenerators.TextAlignmentExtensionsGenerator\EntryCellTextAlignmentExtensions.g.cs(122,153,122,173): error CS0121: The call is ambiguous between the following methods or properties: 'CommunityToolkit.Maui.Markup.TextAlignmentExtensions_EntryCell.TextCenterHorizontal(Microsoft.Maui.Controls.EntryCell)'

So, I would like to know the proper way of linking in a local Class Library into a main .NET MAUI application.

[Overdrive77]

I was trying to find a solution for adding resources to a Class Library, but came across this post instead!

First thing... I don't work for Microsoft and my example isn't the official way of doing things... either way, this is the method I use and hope it helps someone! Btw, the example is using net7.0 and not net6.0.

1. Create a new .Net MAUI Class Library and create a static Helper.cs class.
   The Helper.cs class will house your own custom MauiAppBuilder.
   In there, you include all mandatory nuget dependencies used by your .Net MAUI Class Library (You'll need to view the relevant documentation to correctly link them to the builder setup.)

// Example of Helper.cs
using CommunityToolkit.Maui;
namespace MyClassLibrary
{
    // Create a static helper class
    public static class Helper
    {
	// create your own builder logic here
        public static MauiAppBuilder UseMyClassLibrary(this MauiAppBuilder builder)
        {
            // If your library has any nuget plugin dependencies, add all their documented builder setups here...
            // UseMauiCommunityToolkit is an example, it does report ".UseMauiCommunityToolkit()` must be chained to `.UseMauiApp<T>()" 
            // However, it really should be placed in MauiProgram. Even with the build Output error, the project executes successfully. 
	    builder.UseMauiCommunityToolkit();

            // Add all of your project's library builder stuff here (if any).
            builder.Services.AddTransient<DetailPage>();
			
	    // Return your custom builder object.
            return builder;
        }
    }
}

2. Right-click on the Dependencies folder of your .Net MAUI project and add project MyClassLibrary.

// Inside the Apps MAUIProgram, add the builder .UseMyClassLibrary() inside CreateMauiApp()
using MyClassLibrary;
namespace MyAwesomeApp;

public static class MauiProgram
{
	public static MauiApp CreateMauiApp()
	{
		var builder = MauiApp.CreateBuilder();
		builder
			.UseMauiApp<App>()
			.UseMyClassLibrary() // See Helper.cs
			.ConfigureFonts(fonts =>
			{
				fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
				fonts.AddFont("OpenSans-Semibold.ttf", "OpenSansSemibold");
			});

#if DEBUG
		builder.Logging.AddDebug();
#endif

		return builder.Build();
	}
}

3. Build and run your app.

[jbm-sg]

Hi ! Thanks for your comment, it helped me.

Visual Studio show the error : MCT001 `.UseMauiCommunityToolkit()` must be chained to `.UseMauiApp()`.
I confirme to build of the app with the error.

[sebarslan]

i have the same error:

Visual Studio show the error : MCT001 .UseMauiCommunityToolkit() must be chained to .UseMauiApp().

[gceaser]

In my .Net Maui class library I am trying to use the EventToCommandBehavior. I cannot even compile my class library project as I get the following error:

XFC0000 Cannot resolve type "http://schemas.microsoft.com/dotnet/2022/maui/toolkit:toolkit:EventToCommandBehavior"

I do have the following line in my ContentView XAML page:
xmlns:toolkit="http://schemas.microsoft.com/dotnet/2022/maui/toolkit"