Avalonia+ReactiveUI+SourceGenerators带返回值的异步命令实现

在Avalonia+ReactiveUI+SourceGenerators组合下设计带返回值的异步命令，在不阻塞主线程的情况下执行耗时较长的程序代码，待代码执行完毕后，返回并显示结果，设计一简单示例如下：

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
    {
        [ObservableAsProperty]
        private string _comResult;
        [ReactiveCommand]
        private async Task<string> ComDataAsync()
        {
            // 模拟耗时操作
            await Task.Delay(1000);
            // 模拟数据计算
            return $"数据计算完成: {3+4}";
        }      
        public TestCmdViewModel()
        {
            // _comResultHelper是由ReactiveUI.SourceGenerators.ObservableAsPropertyGenerator生成的可观察属性
            _comResultHelper = ComDataCommand
                .ToProperty(this, x=>x.ComResult, scheduler: RxApp.MainThreadScheduler)；
        }
    }
}

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="测试带返回值的异步命令"
    Width="300"
    Height="400"
    d:DesignHeight="400"
    d:DesignWidth="300"
    x:DataType="vm:TestCmdViewModel"
    mc:Ignorable="d">
    <StackPanel Margin="20" Spacing="10">       
   <Button Content="开始计算" 
            Command="{Binding ComDataCommand}"/>
    <TextBlock Text="{Binding ComResult}" 
               Margin="0,10,0,0"/>    
    </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

通过ReactiveUI.SourceGenerators.ObservableAsPropertyGenerator生成的可观察属性_comResultHelper获取命令的返回值，通过ToProperty方法转化为可绑定属性ComResult。

总结

Avalonia 给你跨平台的舞台，ReactiveUI 给你响应式的灵魂，Source Generators 为你自动生成代码，减少编写繁杂的样板代码烦恼；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。