.NET MAUI 中的异步命令

Question

我似乎在 .NET MAUI 或 .NET MAUI Community Toolkit 中找不到

AsyncCommand

。知道我可以找到什么包/命名空间吗？

Answer 1

https://devblogs.microsoft.com/dotnet/introducing-the-net-maui-community-toolkit-preview/#what-to-expect-in-net-maui-toolkit

.NET MAUI 工具包将不包含 Xamarin 的 MVVM 功能 社区工具包，例如 AsyncCommand。展望未来，我们将添加 将所有 MVVM 特定功能添加到新的 NuGet 包中， 社区工具包.MVVM.

Answer 2

即使问题已被标记为已解决，有人也可能会从 John Thiriet 编写的解决方案中受益。我实施了它并且效果很好。 https://johnthiriet.com/mvvm-going-async-with-async-command/

public interface IAsyncCommand<T> : ICommand
{
    Task ExecuteAsync(T parameter);
    bool CanExecute(T parameter);
}

public class AsyncCommand<T> : IAsyncCommand<T>
{
    public event EventHandler CanExecuteChanged;

    private bool _isExecuting;
    private readonly Func<T, Task> _execute;
    private readonly Func<T, bool> _canExecute;
    private readonly IErrorHandler _errorHandler;

    public AsyncCommand(Func<T, Task> execute, Func<T, bool> canExecute = null, IErrorHandler errorHandler = null)
    {
        _execute = execute;
        _canExecute = canExecute;
        _errorHandler = errorHandler;
    }

    public bool CanExecute(T parameter)
    {
        return !_isExecuting && (_canExecute?.Invoke(parameter) ?? true);
    }

    public async Task ExecuteAsync(T parameter)
    {
        if (CanExecute(parameter))
        {
            try
            {
                _isExecuting = true;
                await _execute(parameter);
            }
            finally
            {
                _isExecuting = false;
            }
        }

        RaiseCanExecuteChanged();
    }

    public void RaiseCanExecuteChanged()
    {
        CanExecuteChanged?.Invoke(this, EventArgs.Empty);
    }

//#region Explicit implementations
    bool ICommand.CanExecute(object parameter)
    {
        return CanExecute((T)parameter);
    }

    void ICommand.Execute(object parameter)
    {
        ExecuteAsync((T)parameter).FireAndForgetSafeAsync(_errorHandler);
    }
//#endregion
}

然后就可以像在 Xamarin 中一样在 MAUI 中使用。

public MyMVVM()
{
   MyCommand = new AsyncCommand(async()=> await MyMethod);
}
...
public AsynCommand MyCommand {get;}

Answer 3

安装CommunityToolkitMVVM 8.0.0

[RelayCommand]
async Task your_method (){...}

Answer 4

将 AsyncAwaitBestPractices.MVVM Nuget 包添加到您的项目中以恢复 AsyncCommand。

有关更多信息，请参阅 Github 项目页面：https://github.com/brminnick/AsyncAwaitBestPractices

Answer 5

1. 安装nuget包CommunityToolkit.Mvvm。
2. 声明 IAsyncRelayCommand 并创建 AsyncRelayCommand 的实例，就像这样：

public IAsyncRelayCommand ScanCommand => this.scanCommand ??= new AsyncRelayCommand(this.ScanNetworksAsync);