C# 自定义无边框窗体阴影效果

工作中我们会经常遇到自定义一些窗口的样式，设置无边框然后自定义关闭、最大化等其他菜单，但是这样就失去了Winform自带的边框阴影效果，下面这个方法能让无边框增加阴影效果。代码如下：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WinfromTest.ShadowDialog
{
    public partial class ShadowForm : Form
    {
        [DllImport("dwmapi.dll")]
        public static extern int DwmExtendFrameIntoClientArea(IntPtr hWnd, ref MARGINS pMarInset);

        [DllImport("dwmapi.dll")]
        public static extern int DwmSetWindowAttribute(IntPtr hwnd, int attr, ref int attrValue, int attrSize);

        [DllImport("dwmapi.dll")]
        public static extern int DwmIsCompositionEnabled(ref int pfEnabled);

        private bool m_aeroEnabled;                     // variables for box shadow
        private const int CS_DROPSHADOW = 0x00020000;
        private const int WM_NCPAINT = 0x0085;
        private const int WM_ACTIVATEAPP = 0x001C;

        public struct MARGINS                           // struct for box shadow
        {
            public int leftWidth;
            public int rightWidth;
            public int topHeight;
            public int bottomHeight;
        }

        private const int WM_NCHITTEST = 0x84;          // variables for dragging the form
        private const int HTCLIENT = 0x1;
        private const int HTCAPTION = 0x2;

        protected override CreateParams CreateParams
        {
            get
            {
                m_aeroEnabled = CheckAeroEnabled();

                CreateParams cp = base.CreateParams;
                if (!m_aeroEnabled)
                    cp.ClassStyle |= CS_DROPSHADOW;

                return cp;
            }
        }

        private bool CheckAeroEnabled()
        {
            if (Environment.OSVersion.Version.Major >= )
            {
                int enabled = ;
                DwmIsCompositionEnabled(ref enabled);
                return enabled ==  ? true : false;
            }
            return false;
        }

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

                    }
                    break;
                default:
                    break;
            }
            base.WndProc(ref m);

            if (m.Msg == WM_NCHITTEST && (int)m.Result == HTCLIENT)     // drag the form
                m.Result = (IntPtr)HTCAPTION;

        }

        public ShadowForm()
        {
            m_aeroEnabled = false;
            FormBorderStyle = FormBorderStyle.None;
            InitializeComponent();
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            Close();
        }

        private void ShadowForm_Resize(object sender, EventArgs e)
        {
            pnlClient.Dock = DockStyle.Top;
            pnlClient.Height = this.Height - ;
        }
    }
}

1.上面代码中MARGINS部分源码里设置的都是1，这样阴影效果中会有一条1像素的白边，如果都设置成0后阴影效果就没了，无奈只能bottomHeight=1，这样只有底部有个小白线。

MARGINS margins = new MARGINS()
                        {
                            bottomHeight = ,
                            leftWidth = ,
                            rightWidth = ,
                            topHeight =
                        };

2.如果窗体上弄个pannel设置成Fill模式，阴影效果也会消失，费解。。。所以不能全部填充满，为此我想了个办法，设计界面还是弄一个pannel设置成FIll模式，这样不影响我们继续在页面布局，但是在ShadowForm_Resize中动态设置Dock为Top，高度为父容器Height -1就可以了。

这样一个自带阴影效果的Form就做好了。

private void ShadowForm_Resize(object sender, EventArgs e)
        {
            pnlClient.Dock = DockStyle.Top;
            pnlClient.Height = this.Height - ;
        }

效果如下：