interaction.cs

using System;
using System.Threading.Tasks;
using System.Windows.Input;

namespace MyAssembly.ViewModels;

/// <summary>
/// Simple implementation of Interaction pattern from ReactiveUI framework.
/// https://www.reactiveui.net/docs/handbook/interactions/
/// </summary>
public sealed class Interaction<TInput, TOutput> : IDisposable, ICommand
{
    private Func<TInput, Task<TOutput>>? _handler;

    public Task<TOutput> Handle(TInput input)
    {
        if (_handler is null)
        {
            throw new InvalidOperationException("Handler wasn't registered");
        }

        return _handler(input);
    }

    public IDisposable RegisterHandler(Func<TInput, Task<TOutput>> handler)
    {
        if (_handler is not null)
        {
            throw new InvalidOperationException("Handler was already registered");
        }

        _handler = handler;
        CanExecuteChanged?.Invoke(this, EventArgs.Empty);
        return this;
    }

    public void Dispose()
    {
        _handler = null;
    }

    public bool CanExecute(object? parameter) => _handler is not null;

    public void Execute(object? parameter) => Handle((TInput?)parameter!);

    public event EventHandler? CanExecuteChanged;
}