RelayCommand.cs (WPF MVVM)

using System;
using System.Windows.Input;

public class RelayCommand<T> : ICommand {
    private readonly Action<T> _execute = null;
    private readonly Func<T, bool> _canExecute = null;

    public RelayCommand(Action<T> execute, Func<T, bool> canExecute = null) {
        _execute = execute ?? throw new ArgumentNullException(nameof(execute));
        _canExecute = canExecute ?? (_ => true);
    }

    public event EventHandler CanExecuteChanged {
        add => CommandManager.RequerySuggested += value;
        remove => CommandManager.RequerySuggested -= value;
    }

    public bool CanExecute(object parameter) => _canExecute((T)parameter);

    public void Execute(object parameter) => _execute((T)parameter);
}

public class RelayCommand : RelayCommand<object> {
    public RelayCommand(Action execute)
        : base(_ => execute()) { }

    public RelayCommand(Action execute, Func<bool> canExecute)
        : base(_ => execute(), _ => canExecute()) { }
}