OBAppSrc/WpfApplicati.../EditINWindow...

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
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.Shapes;

namespace WpfApplication19
{
	/// <summary>
	/// Interaction logic for EditINWindow.xaml
	/// </summary>
	public partial class EditINWindow : Window
	{
		public EditINWindow()
		{
			InitializeComponent();
			var w = (MainWindow)Application.Current.MainWindow;
			grainSizeInput.Text = w.inStarGS;
		}

		private void saveBtn_Click(object sender, RoutedEventArgs e)
		{
			var w = (MainWindow)Application.Current.MainWindow;
			w.inStarGS = grainSizeInput.Text;
			this.Close();
		}

		private void grainSizeInput_PreviewKeyDown(object sender, KeyEventArgs e)
		{
			if ((e.Key >= Key.D0 && e.Key <= Key.D9) || e.Key == Key.Next || e.Key == Key.Back || e.Key == Key.Delete || e.Key == Key.Left || e.Key == Key.Right)
				e.Handled = false;
			else e.Handled = true;
		}
	}
}