添付ビヘイビアでTextBoxにCommandを実装してみた

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Input;
using System.Windows.Controls;
using System.Windows;

namespace SharpLab.IKnow.ItemBankPane {
	public class TextBoxBehavior {

		#region Command

		public static ICommand GetCommand(TextBox textBox) {
			return (ICommand)textBox.GetValue(CommandProperty);
		}

		public static void SetCommand(
		  TextBox textBox, bool value) {
			textBox.SetValue(CommandProperty, value);
		}

		public static readonly DependencyProperty CommandProperty =
			DependencyProperty.RegisterAttached(
			"Command",
			typeof(ICommand),
			typeof(TextBoxBehavior),
			new UIPropertyMetadata(null, OnCommandPropertyChanged));

		static void OnCommandPropertyChanged(DependencyObject depObj, DependencyPropertyChangedEventArgs e) {
			TextBox textBox = depObj as TextBox;
			if (textBox == null)
				return;

			if (e.NewValue is ICommand == false)
				return;

			ICommand command = (ICommand)e.NewValue;

			textBox.KeyDown += new KeyEventHandler(OnTextBoxKeyDown);
		}

		static void OnTextBoxKeyDown(object sender, KeyEventArgs e) {
			TextBox textBox = (TextBox)e.OriginalSource;
			ICommand command = TextBoxBehavior.GetCommand(textBox);
			if (e.Key == Key.Enter && command != null && command.CanExecute(TextBoxBehavior.GetCommandParameter(textBox))) {
				command.Execute(TextBoxBehavior.GetCommandParameter(textBox));
			}
		}

		#endregion

		#region CommandParameter

		public static object GetCommandParameter(TextBox textBox) {
			return textBox.GetValue(CommandParameterProperty);
		}

		public static void SetCommandParameter(
		  TextBox textBox, object value) {
			textBox.SetValue(CommandParameterProperty, value);
		}

		public static readonly DependencyProperty CommandParameterProperty =
			DependencyProperty.RegisterAttached(
			"CommandParameter",
			typeof(object),
			typeof(TextBoxBehavior),
			new UIPropertyMetadata(null));

		#endregion
	}
}

<TextBox v:TextBoxBehavior.Command="{Binding Path=StartSearchCommand}" />