Avalonia+ReactiveUI+Sourcegenerators实现异步命令

1、必要的包引用

    <PackageReference Include="Avalonia" Version="11.3.6" />
    <PackageReference Include="Avalonia.ReactiveUI" Version="11.3.6" />
    <PackageReference Include="ReactiveUI.SourceGenerators" Version="2.4.1">

2、ViewModel (使用 ReactiveUI Source Generators)

using ReactiveUI;
using ReactiveUI.SourceGenerators;
using System;
using System.Threading;
using System.Threading.Tasks;

namespace AvaRea.ViewModels
{
    public partial class TestCmdViewModel: ReactiveObject
    {
        private IObservable<bool> _canExecute;
        private IObservable<bool> _canCancel;
        private  CancellationTokenSource _cancellationTokenSource = new();
        [Reactive] private string _status  = "就绪";
        [Reactive] private bool _isExecuting = false;
        [ObservableAsProperty] private bool _isCancelEnabled =>!_isExecuting;
        [ReactiveCommand(CanExecute = nameof(_canExecute))]
        private async void ExecuteAsync(CancellationToken cancellationToken)
        {
            IsExecuting = true;
            Status = "任务执行中...";
            try
            {
                // 创建新的 CancellationTokenSource 并链接命令的cancellationToken
                _cancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
                // 模拟异步工作
                for (int i = 0; i <= 100; i++)
                {
                    // 检查取消请求
                    _cancellationTokenSource.Token.ThrowIfCancellationRequested();
                    Status = $"进度: {i}%";
                    await Task.Delay(100, cancellationToken); // 模拟工作
                }

                Status = "任务完成!";
            }
            catch (OperationCanceledException)
            {
                Status = "任务已取消";
            }
            finally
            {
                IsExecuting = false;
                _cancellationTokenSource?.Dispose();
                _cancellationTokenSource = null;
            }
        }
        [ReactiveCommand(CanExecute =nameof(_canCancel))]
        private void CancelExecution()
        {
            _cancellationTokenSource?.Cancel();
            Status = "正在取消...";
        }
        public TestCmdViewModel()
        {
            Status = "初始化状态";
            _canExecute= this.WhenAnyValue(x => x.IsExecuting, x =>!x);
            _canCancel = this.WhenAnyValue(x => x.IsExecuting);
        }
    }
}

3、View

<Window
    x:Class="AvaRea.TestCmdView"
    xmlns="https://github.com/avaloniaui"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:vm="clr-namespace:AvaRea.ViewModels"
    Title="测试异步命令"
    Width="300"
    Height="200"
    d:DesignHeight="200"
    d:DesignWidth="300"
    x:DataType="vm:TestCmdViewModel"
    mc:Ignorable="d">
    <StackPanel Margin="20" Spacing="10">
        <TextBlock FontSize="16" Text="{Binding Status}" />
        <StackPanel Orientation="Horizontal" Spacing="10">
            <Button
                Command="{Binding ExecuteAsyncCommand}"
                Content="开始执行" />

            <Button
                Background="Red"
                Command="{Binding CancelExecutionCommand}"
                Content="取消"
                Foreground="White" />
        </StackPanel>
    </StackPanel>
</Window>

4、App.axaml

<Application xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             x:Class="AvaRea.App"
             RequestedThemeVariant="Default">
             <!-- "Default" ThemeVariant follows system theme variant. "Dark" or "Light" are other available options. -->
    <Application.Styles>
	       <FluentTheme />
    </Application.Styles>
</Application>

5、App.axaml.cs

using Avalonia;
using Avalonia.Controls.ApplicationLifetimes;
using Avalonia.Markup.Xaml;
using AvaRea.ViewModels;

namespace AvaRea;

public partial class App : Application
{
    public override void Initialize()
    {
        AvaloniaXamlLoader.Load(this);
    }

    public override void OnFrameworkInitializationCompleted()
    {
        if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
        {
            desktop.MainWindow = new TestCmdView
            {
                DataContext = new TestCmdViewModel()
            };
        }
        else if (ApplicationLifetime is ISingleViewApplicationLifetime singleViewPlatform)
        {
            singleViewPlatform.MainView = new TestCmdView
            {
                DataContext = new TestCmdViewModel()
            };
        }

        base.OnFrameworkInitializationCompleted();
    }
}

6、Program.cs

using System;

using Avalonia;
using Avalonia.ReactiveUI;

namespace AvaRea.Desktop;

class Program
{
    // Initialization code. Don't use any Avalonia, third-party APIs or any
    // SynchronizationContext-reliant code before AppMain is called: things aren't initialized
    // yet and stuff might break.
    [STAThread]
    public static void Main(string[] args) => BuildAvaloniaApp()
        .StartWithClassicDesktopLifetime(args);

    // Avalonia configuration, don't remove; also used by visual designer.
    public static AppBuilder BuildAvaloniaApp()
        => AppBuilder.Configure<App>()
            .UsePlatformDetect()
            .WithInterFont()
            .LogToTrace()
            .UseReactiveUI();
}

7、主要特点

1. CancellationToken 传递: ReactiveCommand 会自动传递 CancellationToken;
2. 取消检查: 在异步方法中定期检查 cancellationToken.ThrowIfCancellationRequested();
3. 状态管理: 使用 IsExecuting 属性并利用ReactiveUI响应式编程特点和Sourcegenerators简化代码的功能控制 UI 状态和命令可用性，无需在axaml代码中进行绑定;
4. 资源清理: 使用 using 语句或 finally 块确保 CancellationTokenSource 被正确清理。

总结

Avalonia 给你跨平台的舞台，ReactiveUI 给你响应式的灵魂，Source Generators 给你自动生成代码；三者合体 = 用最少的代码，写出最快、最稳、最易维护的跨平台 .NET UI。