C# 点击窗口任意位置拖动

代码：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace FreeNotes
{
    public partial class kk : Form
    {
        public kk()
        {
            InitializeComponent();
        }

        [DllImport("user32.dll")]
        public static extern bool ReleaseCapture();

        [DllImport("user32.dll")]
        public static extern bool SendMessage(IntPtr hwnd, int wMsg, int wParam, int lParam);

        private void kk_MouseDown(object sender, MouseEventArgs e)
        {
            ReleaseCapture();
            SendMessage(this.Handle, 0x0112, 0xF012, 0);
        } 
    }
}