用winform實現的類似於WPF中PopUp控制元件的一段程式碼

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

namespace xxxxxxx
{
    /// <summary>
 

    /// 浮動層基類
    /// </summary>
    public class FloatLayerBase : Form
    {
        /// <summary>
        /// 滑鼠訊息篩選器
        /// </summary>
        //由於本窗體為WS_CHILD，所以不會收到在窗體以外點選滑鼠的訊息
        //該訊息篩選器的作用就是讓本窗體獲知滑鼠點選情況，進而根據滑鼠是否在本窗體以外的區域點選，做出相應處理
        readonly AppMouseMessageHandler _mouseMsgFilter;
 


        /// <summary>
        /// 指示本窗體是否已ShowDialog過
        /// </summary>
        //由於多次ShowDialog會使OnLoad/OnShown重入，故需設定此標記以供重入時判斷
        bool _isShowDialogAgain;

        //邊框相關欄位
        BorderStyle _borderType;
        Border3DStyle _border3DStyle;
        ButtonBorderStyle _borderSingleStyle;
 

        Color _borderColor;

        /// <summary>
        /// 獲取或設定邊框型別
        /// </summary>
        [Description("獲取或設定邊框型別。")]
        [DefaultValue(BorderStyle.Fixed3D)]
        public BorderStyle BorderType
        {
            get { return _borderType; }
            set
            {
                if (_borderType == value) { return; }
                _borderType = value;
                Invalidate();
            }
        }

        /// <summary>
        /// 獲取或設定三維邊框樣式
        /// </summary>
        [Description("獲取或設定三維邊框樣式。")]
        [DefaultValue(Border3DStyle.RaisedInner)]
        public Border3DStyle Border3DStyle
        {
            get { return _border3DStyle; }
            set
            {
                if (_border3DStyle == value) { return; }
                _border3DStyle = value;
                Invalidate();
            }
        }

        /// <summary>
        /// 獲取或設定線型邊框樣式
        /// </summary>
        [Description("獲取或設定線型邊框樣式。")]
        [DefaultValue(ButtonBorderStyle.Solid)]
        public ButtonBorderStyle BorderSingleStyle
        {
            get { return _borderSingleStyle; }
            set
            {
                if (_borderSingleStyle == value) { return; }
                _borderSingleStyle = value;
                Invalidate();
            }
        }

        /// <summary>
        /// 獲取或設定邊框顏色（僅當邊框型別為線型時有效）
        /// </summary>
        [Description("獲取或設定邊框顏色（僅當邊框型別為線型時有效）。")]
        [DefaultValue(typeof(Color), "DarkGray")]
        public Color BorderColor
        {
            get { return _borderColor; }
            set
            {
                if (_borderColor == value) { return; }
                _borderColor = value;
                Invalidate();
            }
        }

        protected override sealed CreateParams CreateParams
        {
            get
            {
                CreateParams prms = base.CreateParams;

                //prms.Style = 0;
                //prms.Style |= -2147483648;   //WS_POPUP
                prms.Style |= 0x40000000;      //WS_CHILD  重要，只有CHILD窗體才不會搶父窗體焦點
                prms.Style |= 0x4000000;       //WS_CLIPSIBLINGS
                prms.Style |= 0x10000;         //WS_TABSTOP
                prms.Style &= ~0x40000;        //WS_SIZEBOX       去除
                prms.Style &= ~0x800000;       //WS_BORDER        去除
                prms.Style &= ~0x400000;       //WS_DLGFRAME      去除
                //prms.Style &= ~0x20000;      //WS_MINIMIZEBOX   去除
                //prms.Style &= ~0x10000;      //WS_MAXIMIZEBOX   去除

                prms.ExStyle = 0;
                //prms.ExStyle |= 0x1;         //WS_EX_DLGMODALFRAME 立體邊框
                //prms.ExStyle |= 0x8;         //WS_EX_TOPMOST
                prms.ExStyle |= 0x10000;       //WS_EX_CONTROLPARENT
                //prms.ExStyle |= 0x80;        //WS_EX_TOOLWINDOW
                //prms.ExStyle |= 0x100;       //WS_EX_WINDOWEDGE
                //prms.ExStyle |= 0x8000000;   //WS_EX_NOACTIVATE
                //prms.ExStyle |= 0x4;         //WS_EX_NOPARENTNOTIFY

                return prms;
            }
        }

        //建構函式
        public FloatLayerBase()
        {
            //初始化訊息篩選器。新增和移除在顯示/隱藏時負責
            _mouseMsgFilter = new AppMouseMessageHandler(this);

            //初始化基類屬性
            InitBaseProperties();

            //初始化邊框相關
            _borderType = BorderStyle.Fixed3D;
            _border3DStyle = System.Windows.Forms.Border3DStyle.RaisedInner;
            _borderSingleStyle = ButtonBorderStyle.Solid;
            _borderColor = Color.DarkGray;
        }

        protected override void OnLoad(EventArgs e)
        {
            //防止重入
            if (_isShowDialogAgain) { return; }

            //需得減掉兩層邊框寬度，執行時尺寸才與設計時完全相符，原因不明
            //確定與ControlBox、FormBorderStyle有關，但具體聯絡不明
            if (!DesignMode)
            {
                Size size = SystemInformation.FrameBorderSize;
                this.Size -= size + size;//不可以用ClientSize，後者會根據視窗風格重新調整Size
            }
            base.OnLoad(e);
        }

        protected override void OnShown(EventArgs e)
        {
            //防止重入
            if (_isShowDialogAgain) { return; }

            //在OnShown中為首次ShowDialog設標記
            if (Modal) { _isShowDialogAgain = true; }

            if (!DesignMode)
            {
                //啟用首控制元件
                Control firstControl;
                if ((firstControl = GetNextControl(this, true)) != null)
                {
                    firstControl.Focus();
                }
            }
            base.OnShown(e);
        }

        protected override void WndProc(ref Message m)
        {
            //當本窗體作為ShowDialog彈出時，在收到WM_SHOWWINDOW前，Owner會被Disable
            //故需在收到該訊息後立即Enable它，不然Owner窗體和本窗體都將處於無響應狀態
            if (m.Msg == 0x18 && m.WParam != IntPtr.Zero && m.LParam == IntPtr.Zero
                && Modal && Owner != null && !Owner.IsDisposed)
            {
                if (Owner.IsMdiChild)
                {
                    //當Owner是MDI子窗體時，被Disable的是MDI主窗體
                    //並且Parent也會指向MDI主窗體，故需改回為Owner，這樣彈出窗體的Location才會相對於Owner而非MDIParent
                    NativeMethods.EnableWindow(Owner.MdiParent.Handle, true);
                    NativeMethods.SetParent(this.Handle, Owner.Handle);//只能用API設定Parent，因為模式窗體是TopLevel，.Net拒絕為頂級窗體設定Parent
                }
                else
                {
                    NativeMethods.EnableWindow(Owner.Handle, true);
                }
            }
            base.WndProc(ref m);
        }

        //畫邊框
        protected override void OnPaintBackground(PaintEventArgs e)
        {
            base.OnPaintBackground(e);

            if (_borderType == BorderStyle.Fixed3D)//繪製3D邊框
            {
                ControlPaint.DrawBorder3D(e.Graphics, ClientRectangle, Border3DStyle);
            }
            else if (_borderType == BorderStyle.FixedSingle)//繪製線型邊框
            {
                ControlPaint.DrawBorder(e.Graphics, ClientRectangle, BorderColor, BorderSingleStyle);
            }
        }

        //顯示後新增滑鼠訊息篩選器以開始捕捉，隱藏時則移除篩選器。之所以不放Dispose中是想盡早移除篩選器
        protected override void OnVisibleChanged(EventArgs e)
        {
            if (!DesignMode)
            {
                if (Visible) { Application.AddMessageFilter(_mouseMsgFilter); }
                else { Application.RemoveMessageFilter(_mouseMsgFilter); }
            }
            base.OnVisibleChanged(e);
        }

        //實現窗體客戶區拖動
        //在WndProc中實現這個較麻煩，所以放到這裡做
        protected override void OnMouseDown(MouseEventArgs e)
        {
            //讓滑鼠點選客戶區時達到與點選標題欄一樣的效果，以此實現客戶區拖動
            NativeMethods.ReleaseCapture();
            NativeMethods.SendMessage(Handle, 0xA1/*WM_NCLBUTTONDOWN*/, (IntPtr)2/*CAPTION*/, IntPtr.Zero);

            base.OnMouseDown(e);
        }

        /// <summary>
        /// 顯示為模式窗體
        /// </summary>
        /// <param name="control">顯示在該控制元件下方</param>
        public DialogResult ShowDialog(Control control)
        {
            return ShowDialog(control, 0, control.Height);
        }

        /// <summary>
        /// 顯示為模式窗體
        /// </summary>
        /// <param name="control">觸發彈出窗體的控制元件</param>
        /// <param name="offsetX">相對control水平偏移</param>
        /// <param name="offsetY">相對control垂直偏移</param>
        public DialogResult ShowDialog(Control control, int offsetX, int offsetY)
        {
            return ShowDialog(control, new Point(offsetX, offsetY));
        }

        /// <summary>
        /// 顯示為模式窗體
        /// </summary>
        /// <param name="control">觸發彈出窗體的控制元件</param>
        /// <param name="offset">相對control偏移</param>
        public DialogResult ShowDialog(Control control, Point offset)
        {
            return this.ShowDialogInternal(control, offset);
        }

        /// <summary>
        /// 顯示為模式窗體
        /// </summary>
        /// <param name="item">顯示在該工具欄項的下方</param>
        public DialogResult ShowDialog(ToolStripItem item)
        {
            return ShowDialog(item, 0, item.Height);
        }

        /// <summary>
        /// 顯示為模式窗體
        /// </summary>
        /// <param name="item">觸發彈出窗體的工具欄項</param>
        /// <param name="offsetX">相對item水平偏移</param>
        /// <param name="offsetY">相對item垂直偏移</param>
        public DialogResult ShowDialog(ToolStripItem item, int offsetX, int offsetY)
        {
            return ShowDialog(item, new Point(offsetX, offsetY));
        }

        /// <summary>
        /// 顯示為模式窗體
        /// </summary>
        /// <param name="item">觸發彈出窗體的工具欄項</param>
        /// <param name="offset">相對item偏移</param>
        public DialogResult ShowDialog(ToolStripItem item, Point offset)
        {
            return this.ShowDialogInternal(item, offset);
        }

        /// <summary>
        /// 顯示窗體
        /// </summary>
        /// <param name="control">顯示在該控制元件下方</param>
        public void Show(Control control)
        {
            Show(control, 0, control.Height);
        }

        /// <summary>
        /// 顯示窗體
        /// </summary>
        /// <param name="control">觸發彈出窗體的控制元件</param>
        /// <param name="offsetX">相對control水平偏移</param>
        /// <param name="offsetY">相對control垂直偏移</param>
        public void Show(Control control, int offsetX, int offsetY)
        {
            Show(control, new Point(offsetX, offsetY));
        }

        /// <summary>
        /// 顯示窗體
        /// </summary>
        /// <param name="control">觸發彈出窗體的控制元件</param>
        /// <param name="offset">相對control偏移</param>
        public void Show(Control control, Point offset)
        {
            this.ShowInternal(control, offset);
        }

        /// <summary>
        /// 顯示窗體
        /// </summary>
        /// <param name="item">顯示在該工具欄下方</param>
        public void Show(ToolStripItem item)
        {
            Show(item, 0, item.Height);
        }

        /// <summary>
        /// 顯示窗體
        /// </summary>
        /// <param name="item">觸發彈出窗體的工具欄項</param>
        /// <param name="offsetX">相對item水平偏移</param>
        /// <param name="offsetY">相對item垂直偏移</param>
        public void Show(ToolStripItem item, int offsetX, int offsetY)
        {
            Show(item, new Point(offsetX, offsetY));
        }

        /// <summary>
        /// 顯示窗體
        /// </summary>
        /// <param name="item">觸發彈出窗體的工具欄項</param>
        /// <param name="offset">相對item偏移</param>
        public void Show(ToolStripItem item, Point offset)
        {
            this.ShowInternal(item, offset);
        }

        /// <summary>
        /// ShowDialog內部方法
        /// </summary>
        private DialogResult ShowDialogInternal(Component controlOrItem, Point offset)
        {
            //快速連續彈出本窗體將有可能遇到尚未Hide的情況下再次彈出，這會引發異常，故需做處理
            if (this.Visible) { return System.Windows.Forms.DialogResult.None; }

            this.SetLocationAndOwner(controlOrItem, offset);
            return base.ShowDialog();
        }

        /// <summary>
        /// Show內部方法
        /// </summary>
        private void ShowInternal(Component controlOrItem, Point offset)
        {
            if (this.Visible) { return; }//原因見ShowDialogInternal

            this.SetLocationAndOwner(controlOrItem, offset);
            base.Show();
        }

        /// <summary>
        /// 設定座標及所有者
        /// </summary>
        /// <param name="controlOrItem">控制元件或工具欄項</param>
        /// <param name="offset">相對偏移</param>
        private void SetLocationAndOwner(Component controlOrItem, Point offset)
        {
            Point pt = Point.Empty;

            if (controlOrItem is ToolStripItem)
            {
                ToolStripItem item = (ToolStripItem)controlOrItem;
                pt.Offset(item.Bounds.Location);
                controlOrItem = item.Owner;
            }

            Control c = (Control)controlOrItem;
            pt.Offset(GetControlLocationInForm(c));
            pt.Offset(offset);
            this.Location = pt;

            //設定Owner屬性與Show[Dialog](Owner)有不同，當Owner是MDIChild時，後者會改Owner為MDIParent
            this.Owner = c.FindForm();
        }

        /// <summary>
        /// 獲取控制元件在窗體中的座標
        /// </summary>
        private static Point GetControlLocationInForm(Control c)
        {
            Point pt = c.Location;
            while (!((c = c.Parent) is Form))
            {
                pt.Offset(c.Location);
            }
            return pt;
        }

        #region 遮蔽對本類影響重大的基類方法和屬性

        /// <summary>
        /// 初始化部分基類屬性
        /// </summary>
        private void InitBaseProperties()
        {
            base.ControlBox = false;                           //重要
            //必須得是SizableToolWindow才能支援調整大小的同時，不受SystemInformation.MinWindowTrackSize的限制
            base.FormBorderStyle = System.Windows.Forms.FormBorderStyle.SizableToolWindow;
            base.Text = string.Empty;                          //重要
            base.HelpButton = false;
            base.Icon = null;
            base.IsMdiContainer = false;
            base.MaximizeBox = false;
            base.MinimizeBox = false;
            base.ShowIcon = false;
            base.ShowInTaskbar = false;
            base.StartPosition = FormStartPosition.Manual;     //重要
            base.TopMost = false;
            base.WindowState = FormWindowState.Normal;
        }

        //遮蔽原方法
        [Browsable(false), EditorBrowsable(EditorBrowsableState.Never)]
        [Obsolete("請使用別的過載！", true)]
        public new DialogResult ShowDialog() { throw new NotImplementedException(); }

        [Browsable(false), EditorBrowsable(EditorBrowsableState.Never)]
        [Obsolete("請使用別的過載！", true)]
        public new DialogResult ShowDialog(IWin32Window owner) { throw