ZeroAlloc.Notify

Source-generated, awaitable INotifyPropertyChanged for .NET: await vm.SetNameAsync("Alice") returns only after every async handler has finished, with no reflection and NativeAOT support.

Why ZeroAlloc.Notify

• Setters you can await. Async validation, saving or coordinated state changes complete before the setter returns. CommunityToolkit.Mvvm and PropertyChanged.Fody only offer synchronous notifications.
• 0 B when nobody listens. The generated setter creates event args only when there are subscribers; tests assert 0 B for reference-type and value-type properties. With subscribers, a change costs its args object, 40 B, plus a box per value-type value; tests pin both figures.
• Works under NativeAOT and trimming. All plumbing is generated at compile time; CI publishes and runs a NativeAOT sample on every build.
• Compile-time diagnostics. A class that is not partial, a record, or a stray [ObservableProperty] is reported by the build, not discovered at runtime.

Install

dotnet add package ZeroAlloc.Notify

The source generator ships inside the package.

Quick start

using ZeroAlloc.Notify;

var user = new UserViewModel();

user.PropertyChangedAsync += async (args, ct) =>
{
    await Task.Delay(100, ct);  // e.g. save to a server
    Console.WriteLine($"{args.PropertyName}: {args.OldValue} -> {args.NewValue}, saved");
};

await user.SetNameAsync("Alice");  // returns after the handler has saved
await user.SetAgeAsync(30);

[NotifyPropertyChangedAsync]
public partial class UserViewModel
{
    [ObservableProperty] private string _name = "";
    [ObservableProperty] private int _age;
}

The generator writes the Name and Age properties, the SetNameAsync and SetAgeAsync setters and the PropertyChangedAsync event.

What you get

• Async property notifications, before and after a change: [NotifyPropertyChangedAsync] and [NotifyPropertyChangingAsync]. Observable properties
• Async collection notifications with [NotifyCollectionChangedAsync]. Collection changes
• Async validation through INotifyDataErrorInfoAsync. Validation
• Parallel handlers by default, sequential on request with [InvokeSequentially], and a CancellationToken on every setter. Async notifications
• Build-time checks, ZAN001 to ZAN006. Diagnostics
• Targets netstandard2.0, net8.0 and net10.0.
• Built on ZeroAlloc.AsyncEvents, the async event primitive behind every handler.

Performance

One property change with five handlers attached, .NET 10, all four libraries in one BenchmarkDotNet run. Allocations are exact; the ratio is each library's time against a hand-written INotifyPropertyChanged in the same run. Absolute timings are not published.

Library	Ratio	Allocated	Async handlers
Manual INotifyPropertyChanged	1.00	24 B	no
PropertyChanged.Fody	0.93	0 B	no
CommunityToolkit.Mvvm	1.81	0 B	no
ZeroAlloc.Notify	1.47	40 B	yes

Awaitable handlers have a cost: Notify is slower than hand-written code and Fody, and allocates its args object when someone listens. For purely synchronous view models, Fody is the faster choice. The .NET 8 ratios are in the performance doc. Allocation breakdown, design notes and full numbers: docs/performance.md.

Learn more

• Documentation: notify.zeroalloc.net
• Runnable example: samples/ZeroAlloc.Notify.AotSmoke, published with NativeAOT in CI
• Related packages: ZeroAlloc.AsyncEvents and the rest of the ZeroAlloc family
• Contributing: issues and pull requests are welcome on GitHub
• License: MIT