[Visual C# 2017][WPF] WpfCloseWindowCommandSample

Commands\DelegateCommand_T.cs

using System;
using System.Windows.Input;

namespace WpfCloseWindowCommandSample.Commands
{
    public class DelegateCommand<T> : ICommand
    {
        private Action<T> _execute;
        private Func<T, bool> _canExecute;

        public DelegateCommand(Action<T> execute, Func<T, bool> canExecute)
        {
            _execute = execute;
            _canExecute = canExecute;
        }

        public void Execute(object parameter)
        {
            _execute((T)parameter);
        }

        public bool CanExecute(object parameter)
        {
            return _canExecute((T)parameter);
        }

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

MainWindow.xaml

<Window x:Class="WpfCloseWindowCommandSample.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfCloseWindowCommandSample"
        mc:Ignorable="d"
        xmlns:vm="clr-namespace:WpfCloseWindowCommandSample.ViewModels"
        Title="MainWindow" Height="350" Width="525">

    <Window.DataContext>
        <vm:MainViewModel />
    </Window.DataContext>

    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition />
        </Grid.RowDefinitions>

        <Menu Grid.Row="0" Grid.Column="0">
            <MenuItem Header="ファイル(_F)">
                <MenuItem Header="ウィンドウを閉じる"
                    Command="{Binding Path=CloseWindowCommand}" 
                    CommandParameter="{Binding RelativeSource={
                        RelativeSource Mode=FindAncestor, 
                        AncestorType={x:Type Window}}}" />
            </MenuItem>
        </Menu>

        <TextBox Grid.Row="1" Grid.Column="0" />
    </Grid>
</Window>

MainWindow.xaml.cs

using System.Windows;

namespace WpfCloseWindowCommandSample
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
    }
}

ViewModels\MainViewModel.cs

using System.Windows;

using System.ComponentModel;  // INotifyPropertyChanged

using WpfCloseWindowCommandSample.Commands;

namespace WpfCloseWindowCommandSample.ViewModels
{   
    public class MainViewModel : INotifyPropertyChanged
    {
        // ---------------------------------------------------------------------
        // プロパティ - コマンド

        private DelegateCommand<Window> _closeWindowCommand;
        public DelegateCommand<Window> CloseWindowCommand
        {
            get
            {
                if (_closeWindowCommand == null)
                {
                    _closeWindowCommand = new DelegateCommand<Window>(
                        (window) => this.DoCloseWindow(window),
                        (window) => true
                    );
                }
                return _closeWindowCommand;
            }
        }

        private void DoCloseWindow(Window window)
        {
            window.Close();
        }

        // ---------------------------------------------------------------------
        // コンストラクタ

        public MainViewModel() { }

        // ---------------------------------------------------------------------
        // インターフェースの実装 - INotifyPropertyChanged

        public event PropertyChangedEventHandler PropertyChanged;

        private void OnPropertyChanged(string name)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
        }
    }
}