Hi,

I am trying to customize default windows scrollbar in combobox like below.

public partial class ComboEx : ComboBox
{
    internal ScrollbarEx vScrollBar;
    NativeListWindow listControl;
    public ComboEx()
    {
        InitializeComponent();
        DropDownHeight = 100;
        vScrollBar = new ScrollbarEx();
    }

    protected override void OnPaint(PaintEventArgs pe)
    {
        base.OnPaint(pe);
    }

    protected override void OnHandleCreated(EventArgs e)
    {
        base.OnHandleCreated(e);
        COMBOBOXINFO combInfo = new COMBOBOXINFO();
        combInfo.cbSize = Marshal.SizeOf(combInfo);
        Win32.GetComboBoxInfo( this.Handle, ref combInfo );

        listControl = new NativeListWindow(this, combInfo.hwndList);
    }

    protected override void WndProc(ref Message m)
    {
         if (m.Msg == (Win32.WM_REFLECT + Win32.WM_COMMAND))
        {
            if (Win32.HIWORD( (int)m.WParam ) == Win32.CBN_DROPDOWN)
            {
                COMBOBOXINFO combInfo = new COMBOBOXINFO();
                combInfo.cbSize = Marshal.SizeOf(combInfo);
                Win32.GetComboBoxInfo( this.Handle, ref combInfo );

                vScrollBar.Location = new Point( this.Width-23, 1 );
                vScrollBar.Size = new Size( 23, DropDownHeight );
                vScrollBar.Visible = true;
                Win32.SetParent(vScrollBar.Handle, combInfo.hwndList);
                Win32.ShowWindow(vScrollBar.Handle, ShowWindowCommands.Show);
                Win32.SetWindowPos(vScrollBar.Handle,HWND.TopMost, 155, 1, 23, 105, SetWindowPosFlags.SWP_SHOWWINDOW);
            }
        }
        base.WndProc(ref m);
    }

    // MyNativeWindow class to create a window given a class name.
    [System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
    internal class NativeListWindow : NativeWindow
    {
        // Constant values were found in the "windows.h" header file.
        private const int WS_CHILD = 0x40000000,
                          WS_VISIBLE = 0x10000000,
                          WM_ACTIVATEAPP = 0x001C;

        private int windowHandle;

        private ComboEx parent;

        public NativeListWindow(ComboEx owner,IntPtr handle)
        {
            AssignHandle(handle);
            parent = owner;

        }

        // Listen to when the handle changes to keep the variable in sync
        [System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
        protected override void OnHandleChange()
        {
            windowHandle = (int)this.Handle;
        }

        private void AdjustClientRect(ref RECT rect)
        {
            rect.right -= 23;
        }

        [System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name = "FullTrust")]
        protected override void WndProc(ref Message message)
        {
            // Listen for messages that are sent to the button window. Some messages are sent 
            // to the parent window instead of the button's window. 

            switch (message.Msg)
            {
                case Win32.NCCALCSIZE:
                    {
                        if (message.WParam != IntPtr.Zero)
                        {
                            NCCALCSIZE_PARAMS rcsize = (NCCALCSIZE_PARAMS)Marshal.PtrToStructure(message.LParam, typeof(NCCALCSIZE_PARAMS));
                            AdjustClientRect(ref rcsize.rect0);
                            Marshal.StructureToPtr(rcsize, message.LParam, false);
                        }
                        else
                        {
                            RECT rcsize = (RECT)Marshal.PtrToStructure(message.LParam, typeof(RECT));
                            AdjustClientRect(ref rcsize);
                            Marshal.StructureToPtr(rcsize, message.LParam, false);
                        }
                        message.Result = new IntPtr(1);
                        return;
                        break;
                    }

                    case Win32.WM_NCMOUSEMOVE:
                    {
                        base.WndProc(ref message);
                        Win32.SendMessage(parent.vScrollBar.Handle, (uint)message.Msg, message.WParam, message.LParam);
                        break;
                        break;
                    }
                    case Win32.WM_NCLBUTTONDOWN:
                    {
                        base.WndProc(ref message);
                        Win32.SendMessage(parent.vScrollBar.Handle, (uint)message.Msg, message.WParam, message.LParam);
                        break;
                    }
                    case Win32.WM_NCACTIVATE:
                    {
                        base.WndProc(ref message);
                        Win32.SendMessage(parent.vScrollBar.Handle, (uint)message.Msg, message.WParam, message.LParam);
                        break;
                    }
                    case Win32.WM_NCMOUSELEAVE:
                    {
                        base.WndProc(ref message);
                        Win32.SendMessage(parent.vScrollBar.Handle, (uint)message.Msg, message.WParam, message.LParam);
                        break;
                    }
                    case Win32.WM_NCLBUTTONUP:
                    {
                        base.WndProc(ref message);
                        Win32.SendMessage(parent.vScrollBar.Handle, (uint)message.Msg, message.WParam, message.LParam);
                        break;
                    }
                    case Win32.WM_NCHITTEST:
                    {
                        base.WndProc(ref message);
                        Win32.SendMessage(parent.vScrollBar.Handle, (uint)message.Msg, message.WParam, message.LParam);
                        break;
                    }
                    case Win32.WM_MOUSEMOVE:
                    {
                        base.WndProc(ref message);
                        if ((int)message.LParam > 0)
                        {
                            int x = Win32.LOWORD((int)message.LParam);
                            int y = Win32.HIWORD((int)message.LParam);
                            RECT rect = new RECT(); ;
                            Win32.GetWindowRect(new HandleRef(parent.vScrollBar, parent.vScrollBar.Handle),out rect);
                            Rectangle rc = new Rectangle(parent.vScrollBar.Location.X, parent.vScrollBar.Location.Y,
                                (rect.right - rect.left), (rect.bottom - rect.top));
                            if (rc.Contains(new Point(x, y)))
                            {
                                Win32.SetFocus(parent.vScrollBar.Handle);
                                Win32.SetWindowPos(parent.vScrollBar.Handle, HWND.TopMost, 155, 1, 23, 105, SetWindowPosFlags.SWP_SHOWWINDOW);
                                Win32.SendMessage(parent.vScrollBar.Handle, (uint)message.Msg, message.WParam, message.LParam);
                            }
                        }
                        break;
                    }
            }
            base.WndProc(ref message);
        }
    }
}

In the above code, I did the following
1. created a NativeWindow to catch the messages of combobox listcontrol by assigning combInfo.hwndList handle.
2. Placed my custom scrollbar(ScrollBarEx) in the non-client area of combobox listcontrol.

But my custom scrollbar(ScrollBarEx) doesn't receives any messages or focus. It looks like it is dead.
Please look into this code and share some idea to make the scrollbar live.

Where do the classes NativeListWindow, Win32, ComboBoxInfo, etc. come from? They aren't C# classes. I suspect you want the C++ forum.

The class NativeListWindow inherited from System.Windows.Forms.NativeWindow.
http://msdn.microsoft.com/en-us/library/system.windows.forms.nativewindow.aspx

ComboBoxInfo is the structure contains combo box status information.
http://www.pinvoke.net/default.aspx/Structures/COMBOBOXINFO.html

Win32 is my-own class which encapsulates all unmanaged APIs like SendMessage(),GetComboBoxInfo() and SetFocus() etc.

I need it in C# not in C++.

Edited 3 Years Ago by NidhiSree

This article has been dead for over six months. Start a new discussion instead.