自定义Winform窗体，加阴影效果

1.win32 api 

public class BoxShadow
    {
        public const int CS_DROPSHADOW = 0x00020000;//可用背影框
        public const int WM_NCPAINT = 0x0085;//绘制
        public const int WM_NCHITTEST = 0x84;// 可以拖拽窗体
        public const int HTCLIENT = 0x1;//窗体
        public const int HTCAPTION = 0x2;//窗体标题栏

        [DllImport("dwmapi.dll")]
        public static extern int DwmExtendFrameIntoClientArea(IntPtr hWnd, ref MARGINS pMarInset);

        /// <summary>
        ///     设置窗体属性
        /// </summary>
        /// <param name="hwnd"></param>
        /// <param name="attr"></param>
        /// <param name="attrValue"></param>
        /// <param name="attrSize"></param>
        /// <returns></returns>
        [DllImport("dwmapi.dll")]
        public static extern int DwmSetWindowAttribute(IntPtr hwnd, int attr, ref int attrValue, int attrSize);

        /// <summary>
        /// 复合窗体是否可用
        /// </summary>
        /// <param name="pfEnabled"></param>
        /// <returns></returns>
        [DllImport("dwmapi.dll")]
        public static extern int DwmIsCompositionEnabled(ref int pfEnabled);


        public struct MARGINS    // 背影框 struct
        {
            public int leftWidth;
            public int rightWidth;
            public int topHeight;
            public int bottomHeight;
        }
    }
           

2.自定义窗体

//是否启用Aero
        private bool _mAeroEnabled;

        public virtual bool UserBoxShadow { get; set; }

        protected override CreateParams CreateParams
        {
            get
            {
                if (UserBoxShadow)
                {
                    _mAeroEnabled = CheckAeroEnabled();

                    var cp = base.CreateParams;
                    if (!_mAeroEnabled)
                        cp.ClassStyle |= BoxShadow.CS_DROPSHADOW;

                    return cp;
                }
                return base.CreateParams;
            }
        }

        protected override void WndProc(ref Message m)
        {
            if (UserBoxShadow)
            {
                switch (m.Msg)
                {
                    case BoxShadow.WM_NCPAINT: // box shadow
                        if (_mAeroEnabled)
                        {
                            var v = 2;
                            BoxShadow.DwmSetWindowAttribute(Handle, 2, ref v, 4);
                            var margins = new BoxShadow.MARGINS
                            {
                                bottomHeight = 1,
                                leftWidth = 1,
                                rightWidth = 1,
                                topHeight = 1
                            };
                            BoxShadow.DwmExtendFrameIntoClientArea(Handle, ref margins);

                        }

                        break;
                }
            }

            base.WndProc(ref m);

        }

        private bool CheckAeroEnabled()
        {
            if (Environment.OSVersion.Version.Major >= 6)
            {
                int enabled = 0;
                BoxShadow.DwmIsCompositionEnabled(ref enabled);
                return enabled == 1;
            }

            return false;
        }