private const int CS_DropSHADOW = 0x20000;         private const int GCL_STYLE = (-26);                   [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);   

        private void SetShadow()         {             SetClassLong(this.Handle, GCL_STYLE, GetClassLong(this.Handle, GCL_STYLE) | CS_DropSHADOW);         }  

需要添加命名空间 using System.Runtime.InteropServices;

通过下面代码在构造函数中调用方法 SetShadow();

C# 无边框窗体边框阴影效果的简单实现