WPF MVVMパターンを使わずにルーティングコマンドを理解する

<Window x:Class="WpfCommandSample.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:WpfCommandSample"
        mc:Ignorable="d"
        Title="Command Sample" Height="160" Width="400">
    <Window.CommandBindings>
        <CommandBinding Command="Copy" Executed="OnCopy" CanExecute="OnIsExistText"/>
        <CommandBinding Command="Paste" Executed="OnPaste" CanExecute="OnIsPasteEnabled"/>
        <CommandBinding Command="local:Commands.ResetCommand" Executed="OnReset"/>
    </Window.CommandBindings>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <StackPanel Orientation="Horizontal" Margin="6">
            <Button Content="コピー" Command="Copy" Width="60" Margin="6"/>
            <TextBox x:Name="txtBox" Width="240" Height="30" VerticalContentAlignment="Center"/>
        </StackPanel>
        <StackPanel Grid.Row="1" Orientation="Horizontal" Margin="6">
            <Button Content="貼り付け" Command="Paste" Width="60" Margin="6"/>
            <TextBlock x:Name="txtBlock" Width="240" Height="30" />
        </StackPanel>
        <Button x:Name="btnReset" Grid.Row="2" Content="リセット" Command="local:Commands.ResetCommand" Width="60" Margin="6"/>
    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfCommandSample
{
    /// <summary>
    /// MainWindow.xaml の相互作用ロジック
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            Clipboard.Clear();
        }

        private void OnCopy(object sender, ExecutedRoutedEventArgs e)
        {
            string text = txtBox.Text;

            if (!string.IsNullOrWhiteSpace(text))
            {
                // クリップボードにテキストボックスの文字列を保存する
                Clipboard.SetData(DataFormats.Text, text);
            }
        }

        private void OnIsExistText(object sender, CanExecuteRoutedEventArgs e)
        {
            if(txtBox == null)
            {
                return;
            }
            
            // テキストボックスに空白以外の文字列が入力されていた場合はコピーボタンを有効化する
            e.CanExecute = !string.IsNullOrWhiteSpace(txtBox.Text);
        }

        private void OnPaste(object sender, ExecutedRoutedEventArgs e)
        {
            string text = Clipboard.GetText();
            txtBlock.Text = text;

            // テキストブロックに貼り付けた後はクリップボードをクリアする
            // クリップボードが空なので貼り付けボタンは無効化される
            Clipboard.Clear();
        }

        private void OnIsPasteEnabled(object sender, CanExecuteRoutedEventArgs e)
        {
            string text = Clipboard.GetText();
            
            // クリップボードにテキストが保存されていた場合は貼り付けボタンを有効化する
            e.CanExecute = !string.IsNullOrWhiteSpace(text);
        }

        private void OnReset(object sender, ExecutedRoutedEventArgs e)
        {
            // リセット処理をする
            Clipboard.Clear();
            txtBox.Text = string.Empty;
            txtBlock.Text = string.Empty;
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input; // RoutedUICommand

namespace WpfCommandSample
{
    // ユーザー定義のコマンド
    static class Commands
    {
        static readonly RoutedUICommand _resetCommand = new RoutedUICommand();

        public static RoutedUICommand ResetCommand
        {
            get { return _resetCommand; }
        }
    }
}

<Window x:Class="WpfCommandSample.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:WpfCommandSample"
        mc:Ignorable="d"
        Title="Command Sample" Height="160" Width="400">
    <Window.CommandBindings>
        <CommandBinding Command="Copy" Executed="OnCopy" CanExecute="OnIsExistText"/>
        <CommandBinding Command="Paste" Executed="OnPaste" CanExecute="OnIsPasteEnabled"/>
        <CommandBinding Command="local:Commands.ResetCommand" Executed="OnReset"/>
    </Window.CommandBindings>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <StackPanel Orientation="Horizontal" Margin="6">
            <Button Content="コピー" Command="Copy" Width="60" Margin="6"/>
            <TextBox x:Name="txtBox" Width="240" Height="30" VerticalContentAlignment="Center"/>
        </StackPanel>
        
        <StackPanel Grid.Row="1" Orientation="Horizontal" Margin="6">
            <Button Content="貼り付け" Command="Paste" Width="60" Margin="6"/>
            <TextBlock x:Name="txtBlock" Width="240" Height="30" />
        </StackPanel>
   
        <StackPanel Grid.Row="2" Orientation="Horizontal" Margin="6">
            <Button x:Name="btnReset" Content="リセット" Command="local:Commands.ResetCommand" Width="60" Margin="6"/>
            <Button Content="リセット無効" Command="local:Commands.ResetCommand" CommandParameter="noReset" Width="65" Margin="6"/>
        </StackPanel>
    </Grid>
</Window>