C# realizes clicking and dragging anywhere on the form

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.Navigation;  
using System.Windows.Shapes;  
namespace DragWindowTest  
{  
    /// <summary>  
    /// MainWindow.xaml 的交互逻辑  
    /// </summary>  
    public partial class MainWindow : Window  
    {  
        public MainWindow()  
        {  
            InitializeComponent();  
        }  
        private static bool IsDrag = false;  
        private double enterX;  
        private double enterY;  
        private void Window_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)  
        {  
            IsDrag = true;  
            enterX = e.GetPosition(this).X;  
            enterY = e.GetPosition(this).Y;  
        }  
   
        private void Window_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)  
        {  
            IsDrag = false;  
            enterX = 0;  
            enterY = 0;  
        }  
        private void Window_MouseMove(object sender, MouseEventArgs e)  
        {  
            if (IsDrag)  
            {  
                this.Left += e.GetPosition(this).X - enterX;  
                this.Top += e.GetPosition(this).Y - enterY;  
            }  
        }  
    
    }  
}