perRelayCommandAsync.cs

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

namespace Peregrine.WPF.ViewModel.Command
{
    public class perRelayCommandAsync : perViewModelBase, ICommand
    {
        private readonly Func<Task> _execute;
        private readonly Func<bool> _canExecute;

        public perRelayCommandAsync(Func<Task> execute) : this(execute, null) { }

        public perRelayCommandAsync(Func<Task> execute, Func<bool> canExecute)
        {
            _execute = execute ?? throw new ArgumentNullException(nameof(execute));
            _canExecute = canExecute;
        }

        private bool _isExecuting;

        public bool IsExecuting
        {
            get => _isExecuting;
            set
            {
                if(Set(nameof(IsExecuting), ref _isExecuting, value))
                    RaiseCanExecuteChanged();
            }
        }

        public event EventHandler CanExecuteChanged;

        public bool CanExecute(object parameter) => !IsExecuting 
                                                    && (_canExecute == null || _canExecute());

        public async void Execute(object parameter)
        {
            if (!CanExecute(parameter))
                return;

            IsExecuting = true;
            await _execute().ConfigureAwait(true);
            IsExecuting = false;
        }

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


    public class perRelayCommandAsync<T> : perViewModelBase, ICommand
    {
        private readonly Func<T, Task> _execute;
        private readonly Func<T, bool> _canExecute;

        public perRelayCommandAsync(Func<T, Task> execute) : this(execute, null) { }

        public perRelayCommandAsync(Func<T, Task> execute, Func<T, bool> canExecute)
        {
            _execute = execute ?? throw new ArgumentNullException(nameof(execute));
            _canExecute = canExecute;
        }

        private bool _isExecuting;

        public bool IsExecuting
        {
            get => _isExecuting;
            set
            {
                if (Set(nameof(IsExecuting), ref _isExecuting, value))
                    RaiseCanExecuteChanged();
            }
        }

        public event EventHandler CanExecuteChanged;

        public bool CanExecute(object parameter) => !IsExecuting
                                                    && (_canExecute == null || _canExecute((T)parameter));

        public async void Execute(object parameter)
        {
            IsExecuting = true;
            await _execute((T)parameter).ConfigureAwait(true);
            IsExecuting = false;
        }

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