using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;using System.Runtime.InteropServices;namespace testWinForm{    public partial class Form2 : Form    {        public Form2()        {            InitializeComponent();            SetClassLong(this.Handle, GCL_STYLE, GetClassLong(this.Handle, GCL_STYLE) | CS_DropSHADOW); //API函数加载，实现窗体边框阴影效果        }        #region 窗体边框阴影效果变量申明        const int CS_DropSHADOW = 0x20000;        const int GCL_STYLE = (-26);        //声明Win32 API        [DllImport("user32.dll", CharSet = CharSet.Auto)]        public static extern int SetClassLong(IntPtr hwnd, int nIndex, int dwNewLong);        [DllImport("user32.dll", CharSet = CharSet.Auto)]        public static extern int GetClassLong(IntPtr hwnd, int nIndex);        #endregion        private void Form2_Load(object sender, EventArgs e)        {        }    }} 效果：