CommunityToolkit.Mvvm提供了强大的异步编程支持，通过IAsyncRelayCommand和AsyncRelayCommand等类型，使得在MVVM架构中处理异步操作变得简单而优雅。本文将详细介绍如何在WinForm应用中使用这些特性。

核心组件

主要异步命令类型

IAsyncRelayCommand - 异步命令接口
AsyncRelayCommand - 基础异步命令实现
AsyncRelayCommand<T> - 带参数的异步命令实现

异步命令特性

自动管理执行状态
取消操作支持
异常处理
执行状态追踪

实战示例

基础项目设置

首先创建一个WinForm项目，添加必要的NuGet包：

XML
<PackageReference Include="CommunityToolkit.Mvvm" Version="8.4.0" />

示例ViewModel

C#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using static System.Windows.Forms.VisualStyles.VisualStyleElement;

namespace App13
{
    // ObservableObject 是 CommunityToolkit.Mvvm 提供的基础 ViewModel 类
    public partial class MainViewModel : ObservableObject
    {
        // 使用 ObservableProperty 特性自动实现属性通知
        [ObservableProperty]
        private string status = "就绪";

        [ObservableProperty]
        private bool isLoading;

        // 异步命令 - 基础示例
        private readonly IAsyncRelayCommand loadDataCommand;
        public IAsyncRelayCommand LoadDataCommand => loadDataCommand;

        public MainViewModel()
        {
            // 初始化异步命令
            loadDataCommand = new AsyncRelayCommand(LoadDataAsync);
        }

        // 模拟异步数据加载
        private async Task LoadDataAsync()
        {
            try
            {
                IsLoading = true;
                Status = "正在加载数据...";

                // 模拟耗时操作
                await Task.Delay(2000);

                Status = "数据加载完成！";
            }
            catch (Exception ex)
            {
                MessageBox.Show($"发生错误：{ex.Message}");
                Status = "加载失败";
            }
            finally
            {
                IsLoading = false;
            }
        }
    }
}

带取消功能的高级示例

C#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;

namespace App13
{
    public partial class AdvancedViewModel : ObservableObject
    {
        [ObservableProperty]
        private string progressStatus = "就绪";

        [ObservableProperty]
        private int progressValue;

        // 使用 CancellationTokenSource 支持取消操作
        private CancellationTokenSource? cts;

        // 声明异步命令
        private readonly IAsyncRelayCommand startProcessCommand;
        private readonly IRelayCommand cancelCommand;

        public IAsyncRelayCommand StartProcessCommand => startProcessCommand;
        public IRelayCommand CancelCommand => cancelCommand;

        public AdvancedViewModel()
        {
            startProcessCommand = new AsyncRelayCommand(
                ExecuteLongProcessAsync,
                // 通过判断 cts 是否为 null 来确定命令是否可执行
                () => cts == null
            );

            cancelCommand = new RelayCommand(
                // 取消操作的实现
                () =>
                {
                    cts?.Cancel();
                    cts = null;
                },
                // 只有在进程运行时才能取消
                () => cts != null
            );
        }

        private async Task ExecuteLongProcessAsync()
        {
            try
            {
                // 创建新的 CancellationTokenSource
                cts = new CancellationTokenSource();

                ProgressStatus = "处理中...";
                ProgressValue = 0;

                // 模拟长时间运行的任务
                for (int i = 0; i <= 100; i += 10)
                {
                    // 检查是否请求取消
                    cts.Token.ThrowIfCancellationRequested();

                    ProgressValue = i;
                    await Task.Delay(500, cts.Token);
                }

                ProgressStatus = "处理完成！";
                ProgressValue = 100;
            }
            catch (OperationCanceledException)
            {
                ProgressStatus = "操作已取消";
            }
            catch (Exception ex)
            {
                MessageBox.Show($"发生错误：{ex.Message}");
                ProgressStatus = "处理失败";
            }
            finally
            {
                cts = null;
                // 通知命令可用性变化
                (StartProcessCommand as AsyncRelayCommand)?.NotifyCanExecuteChanged();
                (CancelCommand as RelayCommand)?.NotifyCanExecuteChanged();
            }
        }
    }
}

WinForm界面实现

C#
namespace App13
{
    public partial class Form1 : Form
    {
        private readonly MainViewModel viewModel;
        private readonly AdvancedViewModel advancedViewModel;
        public Form1()
        {
            InitializeComponent();

            // 初始化ViewModel
            viewModel = new MainViewModel();
            advancedViewModel = new AdvancedViewModel();

            // 设置数据绑定
            SetupDataBindings();
        }

        private void SetupDataBindings()
        {
            // 基础示例绑定
            btnLoad.Click += async (s, e) => await viewModel.LoadDataCommand.ExecuteAsync(null);

            // 使用BindingSource实现属性绑定
            var bindingSource = new BindingSource();
            bindingSource.DataSource = viewModel;

            lblStatus.DataBindings.Add("Text", bindingSource, nameof(viewModel.Status));

            // 高级示例绑定
            btnStart.Click += async (s, e) => await advancedViewModel.StartProcessCommand.ExecuteAsync(null);
            btnCancel.Click += (s, e) => advancedViewModel.CancelCommand.Execute(null);

            var advancedBindingSource = new BindingSource();
            advancedBindingSource.DataSource = advancedViewModel;

            progressBar.DataBindings.Add("Value", advancedBindingSource, nameof(advancedViewModel.ProgressValue));
            lblProgressStatus.DataBindings.Add("Text", advancedBindingSource, nameof(advancedViewModel.ProgressStatus));
        }
    }
}

总结

CommunityToolkit.Mvvm提供的异步支持极大地简化了WinForm应用中的异步操作处理。通过AsyncRelayCommand和相关组件，我们可以：

优雅地处理异步操作
轻松实现取消功能
有效管理UI状态
提供良好的用户体验

合理使用这些特性，可以显著提高应用程序的响应性和用户体验。

目录