c# 自定义多选下拉列表2

以下为工作中遇到的，备注一下

先需要几个辅助类

#region GripBounds

using System.Drawing;
internal struct GripBounds
{
    private const int GripSize = 6;
    private const int CornerGripSize = GripSize << 1;

    public GripBounds(Rectangle clientRectangle)
    {
        this.clientRectangle = clientRectangle;
    }

    private Rectangle clientRectangle;
    public Rectangle ClientRectangle
    {
        get { return clientRectangle; }
        //set { clientRectangle = value; }
    }

    public Rectangle Bottom
    {
        get
        {
            Rectangle rect = ClientRectangle;
            rect.Y = rect.Bottom - GripSize + 1;
            rect.Height = GripSize;
            return rect;
        }
    }

    public Rectangle BottomRight
    {
        get
        {
            Rectangle rect = ClientRectangle;
            rect.Y = rect.Bottom - CornerGripSize + 1;
            rect.Height = CornerGripSize;
            rect.X = rect.Width - CornerGripSize + 1;
            rect.Width = CornerGripSize;
            return rect;
        }
    }

    public Rectangle Top
    {
        get
        {
            Rectangle rect = ClientRectangle;
            rect.Height = GripSize;
            return rect;
        }
    }

    public Rectangle TopRight
    {
        get
        {
            Rectangle rect = ClientRectangle;
            rect.Height = CornerGripSize;
            rect.X = rect.Width - CornerGripSize + 1;
            rect.Width = CornerGripSize;
            return rect;
        }
    }

    public Rectangle Left
    {
        get
        {
            Rectangle rect = ClientRectangle;
            rect.Width = GripSize;
            return rect;
        }
    }

    public Rectangle BottomLeft
    {
        get
        {
            Rectangle rect = ClientRectangle;
            rect.Width = CornerGripSize;
            rect.Y = rect.Height - CornerGripSize + 1;
            rect.Height = CornerGripSize;
            return rect;
        }
    }

    public Rectangle Right
    {
        get
        {
            Rectangle rect = ClientRectangle;
            rect.X = rect.Right - GripSize + 1;
            rect.Width = GripSize;
            return rect;
        }
    }

    public Rectangle TopLeft
    {
        get
        {
            Rectangle rect = ClientRectangle;
            rect.Width = CornerGripSize;
            rect.Height = CornerGripSize;
            return rect;
        }
    }
}

#endregion

#region UnsafeMethods

using System;
using System.Drawing;
using System.Runtime.InteropServices;
internal class UnsafeMethods
{
    public static readonly IntPtr TRUE = new IntPtr(1);
    public static readonly IntPtr FALSE = new IntPtr(0);

    public const int WM_LBUTTONDOWN = 0x201;
    public const int WM_RBUTTONDOWN = 0x204;
    public const int WM_MBUTTONDOWN = 0x207;
    public const int WM_NCLBUTTONDOWN = 0x0A1;
    public const int WM_NCRBUTTONDOWN = 0x0A4;
    public const int WM_NCMBUTTONDOWN = 0x0A7;
    public const int WM_NCCALCSIZE = 0x0083;
    public const int WM_NCHITTEST = 0x0084;
    public const int WM_NCPAINT = 0x0085;
    public const int WM_NCACTIVATE = 0x0086;
    public const int WM_MOUSELEAVE = 0x02A3;
    public const int WS_EX_NOACTIVATE = 0x08000000;
    public const int HTTRANSPARENT = -1;
    public const int HTLEFT = 10;
    public const int HTRIGHT = 11;
    public const int HTTOP = 12;
    public const int HTTOPLEFT = 13;
    public const int HTTOPRIGHT = 14;
    public const int HTBOTTOM = 15;
    public const int HTBOTTOMLEFT = 16;
    public const int HTBOTTOMRIGHT = 17;
    public const int WM_USER = 0x0400;
    public const int WM_REFLECT = WM_USER + 0x1C00;
    public const int WM_COMMAND = 0x0111;
    public const int CBN_DROPDOWN = 7;
    public const int WM_GETMINMAXINFO = 0x0024;

    public enum TrackerEventFlags : uint
    {
        TME_HOVER = 0x00000001,
        TME_LEAVE = 0x00000002,
        TME_QUERY = 0x40000000,
        TME_CANCEL = 0x80000000
    }

    [DllImport("user32.dll")]
    public static extern IntPtr GetWindowDC(IntPtr hWnd);

    [DllImport("user32.dll")]
    public static extern int ReleaseDC(IntPtr hwnd, IntPtr hDC);

    [DllImport("user32")]
    public static extern bool TrackMouseEvent(ref TRACKMOUSEEVENT lpEventTrack);

    [DllImport("user32.dll")]
    public static extern bool SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, IntPtr lParam);

    internal static int HIWORD(int n)
    {
        return (n >> 16) & 0xffff;
    }

    internal static int HIWORD(IntPtr n)
    {
        return HIWORD(unchecked((int)(long)n));
    }

    internal static int LOWORD(int n)
    {
        return n & 0xffff;
    }

    internal static int LOWORD(IntPtr n)
    {
        return LOWORD(unchecked((int)(long)n));
    }

    [StructLayout(LayoutKind.Sequential)]
    internal struct TRACKMOUSEEVENT
    {
        public uint cbSize;
        public uint dwFlags;
        public IntPtr hwndTrack;
        public uint dwHoverTime;
    }

    [StructLayout(LayoutKind.Sequential)]
    internal struct MINMAXINFO
    {
        public Point reserved;
        public Size maxSize;
        public Point maxPosition;
        public Size minTrackSize;
        public Size maxTrackSize;
    }

    #region RECT structure

    [StructLayout(LayoutKind.Sequential)]
    internal struct RECT
    {
        public int left;
        public int top;
        public int right;
        public int bottom;

        public RECT(int left, int top, int right, int bottom)
        {
            this.left = left;
            this.top = top;
            this.right = right;
            this.bottom = bottom;
        }

        public Rectangle Rect
        {
            get
            {
                return new Rectangle(
                    this.left,
                    this.top,
                    this.right - this.left,
                    this.bottom - this.top);
            }
        }

        public static RECT FromXYWH(int x, int y, int width, int height)
        {
            return new RECT(x,
                            y,
                            x + width,
                            y + height);
        }

        public static RECT FromRectangle(Rectangle rect)
        {
            return new RECT(rect.Left,
                             rect.Top,
                             rect.Right,
                             rect.Bottom);
        }
    }

    #endregion RECT structure

    #region WINDOWPOS

    [StructLayout(LayoutKind.Sequential)]
    internal struct WINDOWPOS
    {
        internal IntPtr hwnd;
        internal IntPtr hWndInsertAfter;
        internal int x;
        internal int y;
        internal int cx;
        internal int cy;
        internal uint flags;
    }
    #endregion

    #region NCCALCSIZE_PARAMS
    //http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winui/winui/windowsuserinterface/windowing/windows/windowreference/windowstructures/nccalcsize_params.asp
    [StructLayout(LayoutKind.Sequential)]
    public struct NCCALCSIZE_PARAMS
    {
        /// <summary>
        /// Contains the new coordinates of a window that has been moved or resized, that is, it is the proposed new window coordinates.
        /// </summary>
        public RECT rectProposed;
        /// <summary>
        /// Contains the coordinates of the window before it was moved or resized.
        /// </summary>
        public RECT rectBeforeMove;
        /// <summary>
        /// Contains the coordinates of the window's client area before the window was moved or resized.
        /// </summary>
        public RECT rectClientBeforeMove;
        /// <summary>
        /// Pointer to a WINDOWPOS structure that contains the size and position values specified in the operation that moved or resized the window.
        /// </summary>
        public WINDOWPOS lpPos;
    }

    #endregion
}

#endregion

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Text;
using System.Windows.Forms;
using System.Security.Permissions;
using System.Runtime.InteropServices;
using VS = System.Windows.Forms.VisualStyles;

/*
<li>Base class for custom tooltips.</li>
<li>Office-2007-like tooltip class.</li>
*/
namespace ZhuoYueE.Bpc.Controls
{
    /// <summary>
    /// Represents a pop-up window.
    /// </summary>
    [ToolboxItem(false)]
    public partial class PopupForm : ToolStripDropDown
    {
        #region " Fields & Properties "

        private Control content;
        /// <summary>
        /// Gets the content of the pop-up.
        /// </summary>
        public Control Content
        {
            get { return content; }
        }

        private bool fade;
        /// <summary>
        /// Gets a value indicating whether the <see cref="PopupControl.Popup"/> uses the fade effect.
        /// </summary>
        /// <value><c>true</c> if pop-up uses the fade effect; otherwise, <c>false</c>.</value>
        /// <remarks>To use the fade effect, the FocusOnOpen property also has to be set to <c>true</c>.</remarks>
        public bool UseFadeEffect
        {
            get { return fade; }
            set
            {
                if (fade == value) return;
                fade = value;
            }
        }

        private bool focusOnOpen = true;
        /// <summary>
        /// Gets or sets a value indicating whether the content should receive the focus after the pop-up has been opened.
        /// </summary>
        /// <value><c>true</c> if the content should be focused after the pop-up has been opened; otherwise, <c>false</c>.</value>
        /// <remarks>If the FocusOnOpen property is set to <c>false</c>, then pop-up cannot use the fade effect.</remarks>
        public bool FocusOnOpen
        {
            get { return focusOnOpen; }
            set { focusOnOpen = value; }
        }

        private bool acceptAlt = true;
        /// <summary>
        /// Gets or sets a value indicating whether presing the alt key should close the pop-up.
        /// </summary>
        /// <value><c>true</c> if presing the alt key does not close the pop-up; otherwise, <c>false</c>.</value>
        public bool AcceptAlt
        {
            get { return acceptAlt; }
            set { acceptAlt = value; }
        }

        private PopupForm ownerPopup;
        private PopupForm childPopup;

        private bool _resizable;
        private bool resizable;
        /// <summary>
        /// Gets or sets a value indicating whether the <see cref="PopupControl.Popup" /> is resizable.
        /// </summary>
        /// <value><c>true</c> if resizable; otherwise, <c>false</c>.</value>
        public bool Resizable
        {
            get { return resizable && _resizable; }
            set { resizable = value; }
        }

        private ToolStripControlHost host;

        private Size minSize;
        /// <summary>
        /// Gets or sets a minimum size of the pop-up.
        /// </summary>
        /// <returns>An ordered pair of type <see cref="T:System.Drawing.Size" /> representing the width and height of a rectangle.</returns>
        public new Size MinimumSize
        {
            get { return minSize; }
            set { minSize = value; }
        }

        private Size maxSize;
        /// <summary>
        /// Gets or sets a maximum size of the pop-up.
        /// </summary>
        /// <returns>An ordered pair of type <see cref="T:System.Drawing.Size" /> representing the width and height of a rectangle.</returns>
        public new Size MaximumSize
        {
            get { return maxSize; }
            set { maxSize = value; }
        }

        private bool _isOpen;

        public bool IsOpen
        {
            get { return _isOpen; }
        }

        /// <summary>
        /// Gets parameters of a new window.
        /// </summary>
        /// <returns>An object of type <see cref="T:System.Windows.Forms.CreateParams" /> used when creating a new window.</returns>
        protected override CreateParams CreateParams
        {
            [SecurityPermission(SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.UnmanagedCode)]
            get
            {
                CreateParams cp = base.CreateParams;
                cp.ExStyle |= UnsafeMethods.WS_EX_NOACTIVATE;
                return cp;
            }
        }

        #endregion

        #region " Constructors "

        /// <summary>
        /// Initializes a new instance of the <see cref="PopupControl.Popup"/> class.
        /// </summary>
        /// <param name="content">The content of the pop-up.</param>
        /// <remarks>
        /// Pop-up will be disposed immediately after disposion of the content control.
        /// </remarks>
        /// <exception cref="T:System.ArgumentNullException"><paramref name="content" /> is <code>null</code>.</exception>
        public PopupForm(Control content)
        {
            if (content == null)
            {
                throw new ArgumentNullException("content");
            }
            this.content = content;
            this.fade = SystemInformation.IsMenuAnimationEnabled && SystemInformation.IsMenuFadeEnabled;
            this._resizable = true;
            AutoSize = false;
            DoubleBuffered = true;
            ResizeRedraw = true;
            host = new ToolStripControlHost(content);
            Padding = Margin = host.Padding = host.Margin = Padding.Empty;
            MinimumSize = content.MinimumSize;
            content.MinimumSize = content.Size;
            MaximumSize = content.MaximumSize;
            content.MaximumSize = content.Size;
            Size = content.Size;
            content.Location = Point.Empty;
            Items.Add(host);
            content.Disposed += delegate(object sender, EventArgs e)
            {
                content = null;
                Dispose(true);
            };
            content.RegionChanged += delegate(object sender, EventArgs e)
            {
                UpdateRegion();
            };
            content.Paint += delegate(object sender, PaintEventArgs e)
            {
                PaintSizeGrip(e);
            };
            UpdateRegion();
        }

        #endregion

        #region " Methods "

        /// <summary>
        /// Processes a dialog box key.
        /// </summary>
        /// <param name="keyData">One of the <see cref="T:System.Windows.Forms.Keys" /> values that represents the key to process.</param>
        /// <returns>
        /// true if the key was processed by the control; otherwise, false.
        /// </returns>
        protected override bool ProcessDialogKey(Keys keyData)
        {
            if (acceptAlt && ((keyData & Keys.Alt) == Keys.Alt))
            {
                if ((keyData & Keys.F4) != Keys.F4)
                {
                    return false;
                }
                else
                {
                    this.Close();
                }
            }
            return base.ProcessDialogKey(keyData);
        }

        /// <summary>
        /// Updates the pop-up region.
        /// </summary>
        protected void UpdateRegion()
        {
            if (this.Region != null)
            {
                this.Region.Dispose();
                this.Region = null;
            }
            if (content.Region != null)
            {
                this.Region = content.Region.Clone();
            }
        }

        /// <summary>
        /// Shows the pop-up window below the specified control.
        /// </summary>
        /// <param name="control">The control below which the pop-up will be shown.</param>
        /// <remarks>
        /// When there is no space below the specified control, the pop-up control is shown above it.
        /// </remarks>
        /// <exception cref="T:System.ArgumentNullException"><paramref name="control"/> is <code>null</code>.</exception>
        public void Show(Control control)
        {
            Show(control, control.ClientRectangle);
        }

        public void Show(Control control, bool center)
        {
            Show(control, control.ClientRectangle, center);
        }

        /// <summary>
        /// Shows the pop-up window below the specified area of the specified control.
        /// </summary>
        /// <param name="control">The control used to compute screen location of specified area.</param>
        /// <param name="area">The area of control below which the pop-up will be shown.</param>
        /// <remarks>
        /// When there is no space below specified area, the pop-up control is shown above it.
        /// </remarks>
        /// <exception cref="T:System.ArgumentNullException"><paramref name="control"/> is <code>null</code>.</exception>
        public void Show(Control control, Rectangle area)
        {
            Show(control, area, false);
        }

        public void Show(Control control, Rectangle area, bool center)
        {
            if (control == null)
            {
                throw new ArgumentNullException("control");
            }
            SetOwnerItem(control);
            resizableTop = resizableLeft = false;
            Point location = control.PointToScreen(new Point(area.Left, area.Top + area.Height));
            Rectangle screen = Screen.FromControl(control).WorkingArea;
            if (center)
            {
                if (location.X + (area.Width + Size.Width) / 2 > screen.Right)
                {
                    resizableLeft = true;
                    location.X = screen.Right - Size.Width;
                }
                else
                {
                    resizableLeft = true;
                    location.X = location.X - (Size.Width - area.Width) / 2;
                }
            }
            else
            {
                if (location.X + Size.Width > (screen.Left + screen.Width))
                {
                    resizableLeft = true;
                    location.X = (screen.Left + screen.Width) - Size.Width;
                }
            }

            if (location.Y + Size.Height > (screen.Top + screen.Height))
            {
                resizableTop = true;
                location.Y -= Size.Height + area.Height;
            }
            location = control.PointToClient(location);
            Show(control, location, ToolStripDropDownDirection.BelowRight);
        }

        private const int frames = 5;
        private const int totalduration = 100;
        private const int frameduration = totalduration / frames;
        /// <summary>
        /// Adjusts the size of the owner <see cref="T:System.Windows.Forms.ToolStrip" /> to accommodate the <see cref="T:System.Windows.Forms.ToolStripDropDown" /> if the owner <see cref="T:System.Windows.Forms.ToolStrip" /> is currently displayed, or clears and resets active <see cref="T:System.Windows.Forms.ToolStripDropDown" /> child controls of the <see cref="T:System.Windows.Forms.ToolStrip" /> if the <see cref="T:System.Windows.Forms.ToolStrip" /> is not currently displayed.
        /// </summary>
        /// <param name="visible">true if the owner <see cref="T:System.Windows.Forms.ToolStrip" /> is currently displayed; otherwise, false.</param>
        protected override void SetVisibleCore(bool visible)
        {
            double opacity = Opacity;
            if (visible && fade && focusOnOpen) Opacity = 0;
            base.SetVisibleCore(visible);
            if (!visible || !fade || !focusOnOpen) return;
            for (int i = 1; i <= frames; i++)
            {
                if (i > 1)
                {
                    System.Threading.Thread.Sleep(frameduration);
                }
                Opacity = opacity * (double)i / (double)frames;
            }
            Opacity = opacity;
        }

        private bool resizableTop;
        private bool resizableLeft;

        private void SetOwnerItem(Control control)
        {
            if (control == null)
            {
                return;
            }
            if (control is PopupForm)
            {
                PopupForm popupControl = control as PopupForm;
                ownerPopup = popupControl;
                ownerPopup.childPopup = this;
                OwnerItem = popupControl.Items[0];
                return;
            }
            if (control.Parent != null)
            {
                SetOwnerItem(control.Parent);
            }
        }

        /// <summary>
        /// Raises the <see cref="E:System.Windows.Forms.Control.SizeChanged" /> event.
        /// </summary>
        /// <param name="e">An <see cref="T:System.EventArgs" /> that contains the event data.</param>
        protected override void OnSizeChanged(EventArgs e)
        {
            content.MinimumSize = Size;
            content.MaximumSize = Size;
            content.Size = Size;
            content.Location = Point.Empty;
            base.OnSizeChanged(e);
        }

        /// <summary>
        /// Raises the <see cref="E:System.Windows.Forms.ToolStripDropDown.Opening" /> event.
        /// </summary>
        /// <param name="e">A <see cref="T:System.ComponentModel.CancelEventArgs" /> that contains the event data.</param>
        protected override void OnOpening(CancelEventArgs e)
        {
            if (content.IsDisposed || content.Disposing)
            {
                e.Cancel = true;
                return;
            }
            UpdateRegion();
            base.OnOpening(e);
        }

        /// <summary>
        /// Raises the <see cref="E:System.Windows.Forms.ToolStripDropDown.Opened" /> event.
        /// </summary>
        /// <param name="e">An <see cref="T:System.EventArgs" /> that contains the event data.</param>
        protected override void OnOpened(EventArgs e)
        {
            if (ownerPopup != null)
            {
                ownerPopup._resizable = false;
            }
            if (focusOnOpen)
            {
                content.Focus();
            }
            _isOpen = true;
            base.OnOpened(e);
        }

        /// <summary>
        /// Raises the <see cref="E:System.Windows.Forms.ToolStripDropDown.Closed"/> event.
        /// </summary>
        /// <param name="e">A <see cref="T:System.Windows.Forms.ToolStripDropDownClosedEventArgs"/> that contains the event data.</param>
        protected override void OnClosed(ToolStripDropDownClosedEventArgs e)
        {
            if (ownerPopup != null)
            {
                ownerPopup._resizable = true;
            }
            _isOpen = false;
            base.OnClosed(e);
        }

        #endregion

        #region " Resizing Support "

        /// <summary>
        /// Processes Windows messages.
        /// </summary>
        /// <param name="m">The Windows <see cref="T:System.Windows.Forms.Message" /> to process.</param>
        [SecurityPermission(SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.UnmanagedCode)]
        protected override void WndProc(ref Message m)
        {
            if (InternalProcessResizing(ref m, false))
            {
                return;
            }
            base.WndProc(ref m);
        }

        /// <summary>
        /// Processes the resizing messages.
        /// </summary>
        /// <param name="m">The message.</param>
        /// <returns>true, if the WndProc method from the base class shouldn't be invoked.</returns>
        [SecurityPermission(SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.UnmanagedCode)]
        public bool ProcessResizing(ref Message m)
        {
            return InternalProcessResizing(ref m, true);
        }

        [SecurityPermission(SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.UnmanagedCode)]
        private bool InternalProcessResizing(ref Message m, bool contentControl)
        {
            if (m.Msg == UnsafeMethods.WM_NCACTIVATE && m.WParam != IntPtr.Zero && childPopup != null && childPopup.Visible)
            {
                childPopup.Hide();
            }
            if (!Resizable)
            {
                return false;
            }
            if (m.Msg == UnsafeMethods.WM_NCHITTEST)
            {
                return OnNcHitTest(ref m, contentControl);
            }
            else if (m.Msg == UnsafeMethods.WM_GETMINMAXINFO)
            {
                return OnGetMinMaxInfo(ref m);
            }
            return false;
        }

        [SecurityPermission(SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.UnmanagedCode)]
        private bool OnGetMinMaxInfo(ref Message m)
        {
            UnsafeMethods.MINMAXINFO minmax = (UnsafeMethods.MINMAXINFO)Marshal.PtrToStructure(m.LParam, typeof(UnsafeMethods.MINMAXINFO));
            minmax.maxTrackSize = this.MaximumSize;
            minmax.minTrackSize = this.MinimumSize;
            Marshal.StructureToPtr(minmax, m.LParam, false);
            return true;
        }

        private bool OnNcHitTest(ref Message m, bool contentControl)
        {
            int x = UnsafeMethods.LOWORD(m.LParam);
            int y = UnsafeMethods.HIWORD(m.LParam);
            Point clientLocation = PointToClient(new Point(x, y));

            GripBounds gripBouns = new GripBounds(contentControl ? content.ClientRectangle : ClientRectangle);
            IntPtr transparent = new IntPtr(UnsafeMethods.HTTRANSPARENT);

            if (resizableTop)
            {
                if (resizableLeft && gripBouns.TopLeft.Contains(clientLocation))
                {
                    m.Result = contentControl ? transparent : (IntPtr)UnsafeMethods.HTTOPLEFT;
                    return true;
                }
                if (!resizableLeft && gripBouns.TopRight.Contains(clientLocation))
                {
                    m.Result = contentControl ? transparent : (IntPtr)UnsafeMethods.HTTOPRIGHT;
                    return true;
                }
                if (gripBouns.Top.Contains(clientLocation))
                {
                    m.Result = contentControl ? transparent : (IntPtr)UnsafeMethods.HTTOP;
                    return true;
                }
            }
            else
            {
                if (resizableLeft && gripBouns.BottomLeft.Contains(clientLocation))
                {
                    m.Result = contentControl ? transparent : (IntPtr)UnsafeMethods.HTBOTTOMLEFT;
                    return true;
                }
                if (!resizableLeft && gripBouns.BottomRight.Contains(clientLocation))
                {
                    m.Result = contentControl ? transparent : (IntPtr)UnsafeMethods.HTBOTTOMRIGHT;
                    return true;
                }
                if (gripBouns.Bottom.Contains(clientLocation))
                {
                    m.Result = contentControl ? transparent : (IntPtr)UnsafeMethods.HTBOTTOM;
                    return true;
                }
            }
            if (resizableLeft && gripBouns.Left.Contains(clientLocation))
            {
                m.Result = contentControl ? transparent : (IntPtr)UnsafeMethods.HTLEFT;
                return true;
            }
            if (!resizableLeft && gripBouns.Right.Contains(clientLocation))
            {
                m.Result = contentControl ? transparent : (IntPtr)UnsafeMethods.HTRIGHT;
                return true;
            }
            return false;
        }

        private VS.VisualStyleRenderer sizeGripRenderer;
        /// <summary>
        /// Paints the sizing grip.
        /// </summary>
        /// <param name="e">The <see cref="System.Windows.Forms.PaintEventArgs" /> instance containing the event data.</param>
        public void PaintSizeGrip(PaintEventArgs e)
        {
            if (e == null || e.Graphics == null || !resizable)
            {
                return;
            }
            Size clientSize = content.ClientSize;
            using (Bitmap gripImage = new Bitmap(0x10, 0x10))
            {
                using (Graphics g = Graphics.FromImage(gripImage))
                {
                    if (Application.RenderWithVisualStyles)
                    {
                        if (this.sizeGripRenderer == null)
                        {
                            this.sizeGripRenderer = new VS.VisualStyleRenderer(VS.VisualStyleElement.Status.Gripper.Normal);
                        }
                        this.sizeGripRenderer.DrawBackground(g, new Rectangle(0, 0, 0x10, 0x10));
                    }
                    else
                    {
                        ControlPaint.DrawSizeGrip(g, content.BackColor, 0, 0, 0x10, 0x10);
                    }
                }
                GraphicsState gs = e.Graphics.Save();
                e.Graphics.ResetTransform();
                if (resizableTop)
                {
                    if (resizableLeft)
                    {
                        e.Graphics.RotateTransform(180);
                        e.Graphics.TranslateTransform(-clientSize.Width, -clientSize.Height);
                    }
                    else
                    {
                        e.Graphics.ScaleTransform(1, -1);
                        e.Graphics.TranslateTransform(0, -clientSize.Height);
                    }
                }
                else if (resizableLeft)
                {
                    e.Graphics.ScaleTransform(-1, 1);
                    e.Graphics.TranslateTransform(-clientSize.Width, 0);
                }
                e.Graphics.DrawImage(gripImage, clientSize.Width - 0x10, clientSize.Height - 0x10 + 1, 0x10, 0x10);
                e.Graphics.Restore(gs);
            }
        }

        #endregion
    }
}

然后新建一个自定义控件，代码如下

：
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Collections;
using System.Reflection;
using Newtonsoft.Json.Linq;

namespace Controls
{

    /// <summary>
    /// 功能描述:自定义多选下拉框
    /// 作　　者:huangzh
    /// 创建日期:2016-01-04 11:57:13
    /// 任务编号:
    /// </summary>
    public class ComboBoxEx : ComboBox
    {
        PopupForm frmhost;
        TreeView lst = new TreeView();
        /// <summary>
        /// 功能描述:构造方法
        /// 作　　者:huangzh
        /// 创建日期:2016-01-04 11:57:27
        /// 任务编号:
        /// </summary>
        public ComboBoxEx()
        {
            this.DrawMode = DrawMode.OwnerDrawFixed;//只有设置这个属性为OwnerDrawFixed才可能让重画起作用   

            lst.Width = ListWidth == 0 ? this.Width : ListWidth;
            lst.Height = ListHeight == 0 ? 300 : ListHeight;
            lst.CheckBoxes = true;
            lst.ShowLines = false;
            lst.ShowPlusMinus = false;
            lst.ShowRootLines = false;
            lst.KeyUp += new KeyEventHandler(lst_KeyUp);
            lst.AfterCheck += new TreeViewEventHandler(lst_AfterCheck);
            this.DropDownHeight = 1;
            frmhost = new PopupForm(lst);
            //frmhost.Closed += new ToolStripDropDownClosedEventHandler(frmhost_Closed);
            //frmhost.Opened += new EventHandler(frmhost_Opened);
        }

        void lst_KeyUp(object sender, KeyEventArgs e)
        {
            OnKeyUp(e);
        }

        void lst_AfterCheck(object sender, TreeViewEventArgs e)
        {
            if (e.Node.Checked)
            {
                if (Text != "")
                {
                    Text += ",";
                }
                Text += e.Node.Tag.ToString();
            }
            else
            {
                string strValue = e.Node.Tag.ToString().Trim();
                if (Text != "")
                {
                    List<string> strs = Text.Split(',').ToList();
                    strs.Remove("");
                    if (strs.Contains(strValue))
                    {
                        strs.Remove(strValue);
                        Text = string.Join(",", strs);
                    }
                }
            }
        }

        void frmhost_Opened(object sender, EventArgs e)
        {

        }

        void frmhost_Closed(object sender, ToolStripDropDownClosedEventArgs e)
        {

        }

        #region Property
        /// <summary>
        /// 选中项
        /// </summary>
        [Description("选定项的值"), Category("Data")]
        public List<TreeNode> SelectedItems
        {
            get
            {
                List<TreeNode> lsttn = new List<TreeNode>();
                foreach (TreeNode tn in lst.Nodes)
                {
                    if (tn.Checked)
                    {
                        lsttn.Add(tn);
                    }
                }
                return lsttn;
            }
        }

        /// <summary>
        /// 数据源
        /// </summary>
        [Description("数据源"), Category("Data")]
        public new object DataSource
        {
            get;
            set;
        }
        /// <summary>
        /// 显示字段
        /// </summary>
        [Description("显示字段"), Category("Data")]
        public string DisplayFiled
        {
            get;
            set;
        }
        /// <summary>
        /// 值字段
        /// </summary>
        [Description("值字段"), Category("Data")]
        public string ValueFiled
        {
            get;
            set;
        }
        /// <summary>
        /// 列表高度
        /// </summary>
        [Description("列表高度"), Category("Data")]
        public int ListHeight
        {
            get;
            set;
        }

        /// <summary>
        /// 列表宽度
        /// </summary>
        [Description("列表宽度"), Category("Data")]
        public int ListWidth
        {
            get;
            set;
        }
        #endregion

        /// <summary>
        /// 功能描述:绑定数据
        /// 作　　者:huangzh
        /// 创建日期:2016-01-04 10:38:51
        /// 任务编号:
        /// </summary>
        public void DataBind()
        {
            this.BeginUpdate();
            if (DataSource != null)
            {
                if (DataSource is IDataReader)
                {
                    DataTable dataTable = new DataTable();
                    dataTable.Load(DataSource as IDataReader);

                    DataBindToDataTable(dataTable);
                }
                else if (DataSource is DataView || DataSource is DataSet || DataSource is DataTable)
                {
                    DataTable dataTable = null;

                    if (DataSource is DataView)
                    {
                        dataTable = ((DataView)DataSource).ToTable();
                    }
                    else if (DataSource is DataSet)
                    {
                        dataTable = ((DataSet)DataSource).Tables[0];
                    }
                    else
                    {
                        dataTable = ((DataTable)DataSource);
                    }

                    DataBindToDataTable(dataTable);
                }
                else if (DataSource is IEnumerable)
                {
                    DataBindToEnumerable((IEnumerable)DataSource);
                }
                else
                {
                    throw new Exception("DataSource doesn't support data type: " + DataSource.GetType().ToString());
                }
            }
            else
            {
                lst.Nodes.Clear();
            }

            this.EndUpdate();
        }

        /// <summary>
        /// 功能描述:绑定Table数据
        /// 作　　者:huangzh
        /// 创建日期:2016-01-04 10:47:27
        /// 任务编号:
        /// </summary>
        /// <param name="dt">dt</param>
        private void DataBindToDataTable(DataTable dt)
        {
            foreach (DataRow dr in dt.Rows)
            {
                TreeNode tn = new TreeNode();
                if (!string.IsNullOrEmpty(DisplayFiled) && !string.IsNullOrEmpty(ValueFiled))
                {
                    tn.Text = dr[DisplayFiled].ToString();
                    tn.Tag = dr[ValueFiled].ToString();
                }
                else if (string.IsNullOrEmpty(ValueFiled))
                {
                    tn.Text = dr[DisplayFiled].ToString();
                    tn.Tag = dr[DisplayFiled].ToString();
                }
                else if (string.IsNullOrEmpty(DisplayFiled))
                {
                    tn.Text = dr[ValueFiled].ToString();
                    tn.Tag = dr[ValueFiled].ToString();
                }
                else
                {
                    throw new Exception("ValueFiled和DisplayFiled至少保证有一项有值");
                }
                tn.ToolTipText = tn.Text;

                tn.Checked = false;
                lst.Nodes.Add(tn);
            }
        }

        /// <summary>
        /// 绑定到可枚举类型
        /// </summary>
        /// <param name="enumerable">可枚举类型</param>
        private void DataBindToEnumerable(IEnumerable enumerable)
        {
            IEnumerator enumerator = enumerable.GetEnumerator();
            while (enumerator.MoveNext())
            {
                object currentObject = enumerator.Current;
                lst.Nodes.Add(CreateListItem(currentObject));
            }
        }


        /// <summary>
        /// 功能描述:获取一个CheckBox
        /// 作　　者:huangzh
        /// 创建日期:2016-01-04 10:53:12
        /// 任务编号:
        /// </summary>
        /// <param name="obj">obj</param>
        /// <returns>返回值</returns>
        private TreeNode CreateListItem(Object obj)
        {
            TreeNode item = new TreeNode();

            if (obj is string)
            {
                item.Text = obj.ToString();
                item.Tag = obj.ToString();
            }
            else
            {
                if (DisplayFiled != "")
                {
                    item.Text = GetPropertyValue(obj, DisplayFiled);
                }
                else
                {
                    item.Text = obj.ToString();
                }

                if (ValueFiled != "")
                {
                    item.Tag = GetPropertyValue(obj, ValueFiled);
                }
                else
                {
                    item.Tag = obj.ToString();
                }
            }
            item.ToolTipText = item.Text;
            return item;
        }

        /// <summary>
        /// 取得属性值
        /// </summary>
        /// <param name="obj"></param>
        /// <param name="propertyName"></param>
        private string GetPropertyValue(object obj, string propertyName)
        {
            object result = null;

            result = ObjectUtil.GetPropertyValue(obj, propertyName);
            return result == null ? String.Empty : result.ToString();
        }

        #region override

        /// <summary>
        /// 功能描述:OnKeyUp
        /// 作　　者:huangzh
        /// 创建日期:2016-01-04 11:58:33
        /// 任务编号:
        /// </summary>
        /// <param name="e">e</param>
        protected override void OnKeyUp(KeyEventArgs e)
        {
            base.OnKeyDown(e);
            bool Pressed = (e.Control && ((e.KeyData & Keys.A) == Keys.A));
            if (Pressed)
            {
                this.Text = "";
                for (int i = 0; i < lst.Nodes.Count; i++)
                {
                    lst.Nodes[i].Checked = true;
                }
            }
        }

        /// <summary>
        /// 功能描述:OnDropDown
        /// 作　　者:huangzh
        /// 创建日期:2016-01-04 11:58:53
        /// 任务编号:
        /// </summary>
        /// <param name="e">e</param>
        protected override void OnDropDown(EventArgs e)
        {
            this.DroppedDown = false;
            string strValue = this.Text;
            if (!string.IsNullOrEmpty(strValue))
            {
                List<string> lstvalues = strValue.Split(',').ToList<string>();
                foreach (TreeNode tn in lst.Nodes)
                {
                    if (tn.Checked && !lstvalues.Contains(tn.Tag.ToString()) && !string.IsNullOrEmpty(tn.Tag.ToString().Trim()))
                    {
                        tn.Checked = false;
                    }
                    else if (!tn.Checked && lstvalues.Contains(tn.Tag.ToString()) && !string.IsNullOrEmpty(tn.Tag.ToString().Trim()))
                    {
                        tn.Checked = true;
                    }
                }
            }
            else
            {
                foreach (TreeNode tn in lst.Nodes)
                {
                    tn.Checked = false;
                }
            }
            frmhost.Show(this);
        }
        #endregion
    }


    /// <summary>
    /// 对象帮助类
    /// </summary>
    public class ObjectUtil
    {
        /// <summary>
        /// 获取对象的属性值
        /// </summary>
        /// <param name="obj">可能是DataRowView或一个对象</param>
        /// <param name="propertyName">属性名</param>
        /// <returns>属性值</returns>
        public static object GetPropertyValue(object obj, string propertyName)
        {
            object result = null;

            try
            {
                if (obj is DataRow)
                {
                    result = (obj as DataRow)[propertyName];
                }
                else if (obj is DataRowView)
                {
                    result = (obj as DataRowView)[propertyName];
                }
                else if (obj is JObject)
                {
                    result = (obj as JObject).Value<JValue>(propertyName).Value; //.getValue(propertyName);
                }
                else
                {
                    result = GetPropertyValueFormObject(obj, propertyName);
                }
            }
            catch (Exception)
            {
                // 找不到此属性
            }

            return result;
        }

        /// <summary>
        /// 获取对象的属性值
        /// </summary>
        /// <param name="obj">对象</param>
        /// <param name="propertyName">属性名（"Color"、"BodyStyle"或者"Info.UserName"）</param>
        /// <returns>属性值</returns>
        private static object GetPropertyValueFormObject(object obj, string propertyName)
        {
            object rowObj = obj;
            object result = null;

            if (propertyName.IndexOf(".") > 0)
            {
                string[] properties = propertyName.Split('.');
                object tmpObj = rowObj;

                for (int i = 0; i < properties.Length; i++)
                {
                    PropertyInfo property = tmpObj.GetType().GetProperty(properties[i], BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
                    if (property != null)
                    {
                        tmpObj = property.GetValue(tmpObj, null);
                    }
                }

                result = tmpObj;
            }
            else
            {
                PropertyInfo property = rowObj.GetType().GetProperty(propertyName, BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
                if (property != null)
                {
                    result = property.GetValue(rowObj, null);
                }
            }

            return result;
        }
    }
}

然后就是使用了，直接拖一个到界面上，然后设置值就可以了

ListHeight，ListWidth 这两个属性一定要修改下的哦

然后就是绑定数据源

  var varSourceFrom = from p in lstEnumEnitty
                                    where p.Type == "source"
                                    select p;
                cboSourceFromType.DataSource = varSourceFrom;
                cboSourceFromType.DisplayFiled = "Name";
                cboSourceFromType.ValueFiled = "Code";
                cboSourceFromType.DataBind();

效果就是这样的了

需要引用的一个DLL去我的上一个文章里面下载吧