No parameterless constructor defined for type 'CommunityToolkit.Maui.Behaviors.TouchBehavior' on iOS (.NET 10)

[pallav1111]

I am encountering a runtime crash on iOS when navigating to a page that utilizes CommunityToolkit.Maui.Behaviors.TouchBehavior in XAML. The exception indicates that the parameterless constructor cannot be found, which appears to be a result of aggressive trimming by the .NET 10 compiler.

Environment:

• .NET SDK: 10.0.102
• MAUI Workload: 10.0.1 (SDK 10.0.100)
• Target Framework: net10.0-ios
• Xcode: 26.2 (Build 17C52)
• NuGet Packages:
• CommunityToolkit.Maui: 14.0.0
• Microsoft.Maui.Controls: 10.0.30

Expected Behavior:
The page should load normally, and the TouchBehavior should be applied to the specified elements.

Actual Behavior:
The app crashes immediately with a Microsoft.Maui.Controls.Xaml.XamlParseException, wrapping a System.MissingMethodException.

Stack Trace:

Microsoft.Maui.Controls.Xaml.XamlParseException: Position 17:22. No parameterless constructor defined for type 'CommunityToolkit.Maui.Behaviors.TouchBehavior'.
 ---> System.MissingMethodException: No parameterless constructor defined for type 'CommunityToolkit.Maui.Behaviors.TouchBehavior'.
   at System.RuntimeType.CreateInstanceMono(Boolean nonPublic, Boolean wrapExceptions)
   at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean wrapExceptions)
   at Microsoft.Maui.Controls.Xaml.CreateValuesVisitor.Visit(ElementNode node, INode parentNode)
   ...
   at ui_feat.Views.BaseAdapterOverviewPage.InitializeComponent()

Additional Context:
It seems the linker (ILLink) is stripping the constructor because it isn't explicitly referenced in C# code, only in XAML. While using _ = new TouchBehavior(); in the code-behind acts as a workaround, the library components should ideally be marked to preserve their constructors during full trimming, or the toolkit should provide a [DynamicallyAccessedMembers] hint for XAML-based instantiation.

[pictos]

If you add x:Name or in some point on your code you add _ = new TouchBehavior() does it work?

[pallav1111]

Already tried, but not worked. do i need to add on my each project? because i have multiple lib projects which contains feature wise UI?

[pictos]

To apply on all projects you can create a Directory.Build.Props at your root folder, like we did with the linked file, all project will import that file and its configurations

[pallav1111]

Okay let me check by adding as you suggest and get back to you soon.

[pallav1111]

@pictos, Thanks for the guidance.

Its working after adding new maui xaml source generator to my each UI projects.

For who facing same issue, define such property as below in your UI or MAUI project :

<MauiXamlInflator>SourceGen</MauiXamlInflator>
<MauiStrictXamlCompilation>true</MauiStrictXamlCompilation>
<MauiEnableXamlCBindingWithSourceCompilation>true</MauiEnableXamlCBindingWithSourceCompilation>

[pallav1111]

@pictos,
I think you confused what happens, let me know if you want to know anything else.

So, what happens here, after adding new source generator it initiates behaviour in C# generated class i believe thus not throwing such error, So, we can say issue is still there if i not use source gen, or not initialised before use. IL still removing it, if you want to investigate more on it.

[pictos]

@pallav1111 I did understand the issue, if you provide a small project that reproduces the issue I'm happy to take a look