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[Bug] RelayCommand Source Generator Fails Silently for Methods Starting With ‘On' #1215
Description
Describe the bug
Methods annotated with [RelayCommand] whose names start with On fail to generate command properties.
The documentation states that:
The name of the generated command will be created based on the method name. The generator will use the method name and append "Command" at the end, and it will strip the "On" prefix, if present. Additionally, for asynchronous methods, the "Async" suffix is also stripped before "Command" is appeneded.
However, the actual behaviour I am experiencing contradicts this claim.
Regression
No response
Steps to reproduce
Prerequisites:
- .NET 10
- C# 13
- Create a new Avalonia (Ver. 12.1.3) desktop project. Your project file should include:
<TargetFramework>net10.0</TargetFramework>
<RuntimeIdentifier>win-x64</RuntimeIdentifier>
-
Add the
CommunityToolkit.Mvvm(Ver. 8.4.2) NuGet package. -
Create a ViewModel with
[RelayCommand]methods starting withOn.
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using System.Diagnostics;
namespace MyTestApp.Avalonia.ViewModels;
public partial class TestViewModel : ObservableObject
(etc.)
[RelayCommand]
private void OnPointerPressed()
{
Debug.WriteLine("Pointer pressed.");
}
[RelayCommand]
private void AsdfPointerPressed()
{
Debug.WriteLine("Pointer pressed.");
}
- Create a
TestView. Attempt to bind toOnPointerPressedCommand.
<Window
x:Class="MyTestApp.Avalonia.Views.TestView"
xmlns="https://github.com/avaloniaui"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:vm="using:MyTestApp.Avalonia.ViewModels"
Name="TestView"
x:DataType="vm:TestViewModel">
<!-- This binding will fail to compile. -->
<Button Command="{Binding OnPointerPressedCommand}" />
<!-- This binding will compile successfully. -->
<Button Command="{Binding AsdfPointerPressedCommand}" />
</Window>
Expected behavior
In the ViewModel, [RelayCommand] private void OnPointerPressed() { } would generate a PointerPressedCommand property, which the View could then execute.
Screenshots
No response
IDE and version
VS 2022
IDE version
18.10.2
Nuget packages
- CommunityToolkit.Common
- CommunityToolkit.Diagnostics
- CommunityToolkit.HighPerformance
- CommunityToolkit.Mvvm (aka MVVM Toolkit)
Nuget package version(s)
8.4.2
Additional context
No response
Help us help you
No, just wanted to report this
Activity
tevinch commentedon Oct 24, 2026
The XAML in step 4 still includes the
Onprefix:For your
OnPointerPressed()method, the generated property isPointerPressedCommand, matching the expected behavior you described. The binding should therefore be:The method itself can stay named
OnPointerPressed.AsdfPointerPressed()keeps its prefix and generatesAsdfPointerPressedCommand.I checked this with a complete compiled-XAML example using the same Toolkit 8.4.2, .NET 10 and C# 13, with Avalonia 12.1.4. The original binding fails compilation with
AVLN2000for the missing member; the corrected binding builds, and actual Avalonia headless pointer clicks execute the command and update the displayed count from 0 to 1 to 2. Replacing the DataContext and clicking again also works.That is scripted headless validation on macOS, not a Windows run of your application. Your report uses Avalonia 12.1.3, so please check the corrected property name there first. If it still fails, the build diagnostic and generated members would help distinguish a separate problem from this binding-name mismatch.
JosiahDanger commentedon Oct 24, 2026
To @tevinch,
Thank you for your response and investigation.
I'm very sorry. I misunderstood the documentation.
I revisited my instructions. I can confirm that binding to
PointerPressedCommandis now successful. For some reason, I was trying to bind toOnPointerPressedCommand.You may close this Issue.