MvvmAIO.Prism.Bcl.Commands 0.2.2

Prism.SourceGenerators

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Roslyn source generators for the Prism MVVM library.

CI Status

• Open the workflow page above to see the latest pipeline status.
• The Tests badge displays the latest passed/failed/skipped counts.
• The run also uploads a test-results artifact (.trx) for detailed test reports.

Project Structure

Prism.SourceGenerators/                        # Shared project (.shproj/.projitems/.props + source code)
Prism.SourceGenerators.Roslyn4001/             # Roslyn 4.0.1
Prism.SourceGenerators.Roslyn4031/             # Roslyn 4.3.1
Prism.SourceGenerators.Roslyn4120/             # Roslyn 4.12.0
Prism.SourceGenerators.Roslyn5000/             # Roslyn 5.0.0
Prism.Core/                                    # MvvmAIO.Prism.Core (attributes), bundled in MvvmAIO.Prism.SourceGenerators
Prism.Bcl.Commands/                            # MvvmAIO.Prism.Bcl.Commands (Prism 8 AsyncDelegateCommand package, install manually)
Prism.SourceGenerators.Samples.Prism9/         # Avalonia 12 sample (Prism 9.0, native AsyncDelegateCommand)
Prism.SourceGenerators.Samples.Prism8/         # Avalonia 12 sample (Prism 8.1.97; same MSBuild lib selection as the NuGet package)

Generators

[ObservableProperty]

Generates observable properties for classes inheriting from BindableBase. Supports two usage modes depending on the C# language version.

Field target (all C# versions)

Annotate a private field with [ObservableProperty] to generate a public property that calls SetProperty in the setter.

// C# 12 or earlier
using Prism.SourceGenerators;

public partial class MainViewModel : BindableBase
{
    [ObservableProperty]
    private string _title = "Hello";

    // Generated: public string Title { get => _title; set => SetProperty(ref _title, value); }
}

Partial property target (C# 13+ with field keyword)

Annotate a partial property with [ObservableProperty] to generate the implementing declaration using the field keyword (semi-auto property).

// C# 13+ / .NET 9+ (requires LangVersion 13.0+ or preview)
using Prism.SourceGenerators;

public partial class MainViewModel : BindableBase
{
    [ObservableProperty]
    public partial string Title { get; set; } = "Hello";

    // Generated: public partial string Title { get => field; set => SetProperty(ref field, value); }
}

The partial property approach eliminates the need for a separate backing field and provides a cleaner API surface. Both modes can coexist in the same project.

OnChanged partial methods

For every [ObservableProperty], the generator emits two partial method declarations that you can optionally implement to react to changes:

public partial class MainViewModel : BindableBase
{
    [ObservableProperty]
    public partial int Age { get; set; }

    // Generated declarations (implement one or both):
    // partial void OnAgeChanged(int value);
    // partial void OnAgeChanged(int oldValue, int newValue);

    partial void OnAgeChanged(int oldValue, int newValue)
    {
        Debug.WriteLine($"Age changed from {oldValue} to {newValue}");
    }
}

The generated setter uses EqualityComparer<T>.Default.Equals for change detection and calls both OnChanged overloads before raising PropertyChanged.

[NotifyPropertyChangedFor]

Apply to a field or partial property alongside [ObservableProperty] to automatically raise PropertyChanged for additional dependent properties when the annotated property changes.

public partial class MainViewModel : BindableBase
{
    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(FullName))]
    private string _firstName = "";

    [ObservableProperty]
    [NotifyPropertyChangedFor(nameof(FullName))]
    private string _lastName = "";

    public string FullName => $"{FirstName} {LastName}";
}

Supports multiple property names via [NotifyPropertyChangedFor(nameof(A), nameof(B))] or multiple attribute instances.

[DelegateCommand]

Generates DelegateCommand or AsyncDelegateCommand properties from methods.

• Synchronous methods (void) generate DelegateCommand / DelegateCommand<T>
• Async methods (Task) generate AsyncDelegateCommand / AsyncDelegateCommand<T>
• For Prism < 9.0, use NuGet MvvmAIO.Prism.SourceGenerators, which adds MvvmAIO.Prism.Core for source-generator attributes. For Prism.Core 8.1.97 async commands, install MvvmAIO.Prism.Bcl.Commands manually so AsyncDelegateCommand exists. If those assemblies are missing while async commands are used, PSG3002 is reported.
• C# 14+: Command properties use the field keyword (no separate backing field)
• C# 13 and earlier: Command properties use a traditional backing field

using Prism.SourceGenerators;

public partial class MainViewModel : BindableBase
{
    // Generates: DelegateCommand IncrementCommand
    [DelegateCommand]
    private void Increment() { /* ... */ }

    // Generates: AsyncDelegateCommand LoadDataCommand
    [DelegateCommand]
    private async Task LoadDataAsync() { /* ... */ }

    // With CanExecute support
    [DelegateCommand(CanExecute = nameof(CanSubmit))]
    private void Submit() { /* ... */ }
    private bool CanSubmit() => true;
}

Generated output comparison

C# 14+ (LangVersion >= 14) — uses field keyword:

// No backing field needed
public DelegateCommand IncrementCommand => field ??= new DelegateCommand(Increment);

C# 13 and earlier — traditional backing field:

private DelegateCommand? _incrementCommand;
public DelegateCommand IncrementCommand => _incrementCommand ??= new DelegateCommand(Increment);

[AsyncDelegateCommand]

Dedicated attribute for async methods with advanced Prism-style features. On Prism 9+, uses the framework types; on Prism 8.1.97, install MvvmAIO.Prism.Bcl.Commands for the same fluent surface: EnableParallelExecution, CancelAfter, Catch, CancellationTokenSourceFactory, and ObservesCanExecute.

using Prism.SourceGenerators;

public partial class MainViewModel : BindableBase
{
    // Parallel execution enabled
    [AsyncDelegateCommand(EnableParallelExecution = true)]
    private async Task FetchDataAsync() { /* ... */ }

    // With error handling and CanExecute
    [AsyncDelegateCommand(CanExecute = nameof(CanSave), Catch = nameof(HandleError))]
    private async Task SaveAsync() { /* ... */ }

    private bool CanSave() => true;
    private void HandleError(Exception ex) { /* ... */ }
}

[ObservesProperty]

Automatically re-evaluates CanExecute when the specified properties change. Works with both [DelegateCommand] and [AsyncDelegateCommand].

using Prism.SourceGenerators;

public partial class MainViewModel : BindableBase
{
    [ObservableProperty]
    private bool _isValid;

    [DelegateCommand(CanExecute = nameof(CanSubmit))]
    [ObservesProperty(nameof(IsValid))]
    private void Submit() { /* ... */ }

    // Multiple properties
    [AsyncDelegateCommand(CanExecute = nameof(CanSave))]
    [ObservesProperty(nameof(Counter), nameof(IsActive))]
    private async Task SaveAsync() { /* ... */ }
}

[BindableBase]

Apply to a class that does not inherit from Prism.Mvvm.BindableBase to automatically generate an INotifyPropertyChanged implementation. The generated code includes PropertyChanged event, SetProperty<T>, RaisePropertyChanged, and OnPropertyChanged methods.

using Prism.SourceGenerators;

[BindableBase]
public partial class SimpleViewModel
{
    private string _message = "Hello!";

    public string Message
    {
        get => _message;
        set => SetProperty(ref _message, value);
    }
}

If the class already inherits from BindableBase or a base class that implements INotifyPropertyChanged, no code is generated.

Diagnostics

Installation

<PackageReference Include="MvvmAIO.Prism.SourceGenerators" Version="0.2.0" />

Or:

dotnet add package MvvmAIO.Prism.SourceGenerators

Building

dotnet build Prism.SourceGenerators.slnx

Nuke Build

This repository uses Nuke as the build orchestration layer for local automation and CI.

• Main source solution: Prism.SourceGenerators.slnx
• Build automation solution: build.slnx (contains only build/_build.csproj)

Common commands:

# CI pipeline locally (clean + restore + compile + test)
dotnet run --project build/_build.csproj -- --target Ci --configuration Release

# Pack NuGet package (optionally override version)
dotnet run --project build/_build.csproj -- --target Pack --configuration Release --version 0.2.0

# Publish NuGet packages (MvvmAIO.Prism.SourceGenerators + MvvmAIO.Prism.Bcl.Commands)
dotnet run --project build/_build.csproj -- --target Publish --configuration Release --version 0.2.0 --nuget-api-key <NUGET_API_KEY>

Requirements

• .NET 10 SDK
• Visual Studio 2022 17.13+ / Rider / VS Code with C# Dev Kit (for .slnx support)