using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Text;
using System.Windows.Forms;





namespace PocketPCTest
{   
    public partial class VirtualListBox : ListBox
    {
        /*
        * Listbox Styles
        */
        private const int LBS_NOTIFY = 0x0001;
        private const int LBS_SORT = 0x0002;
        private const int LBS_NOREDRAW = 0x0004;
        private const int LBS_MULTIPLESEL = 0x0008;
        private const int LBS_OWNERDRAWFIXED = 0x0010;
        private const int LBS_OWNERDRAWVARIABLE = 0x0020;
        private const int LBS_HASSTRINGS = 0x0040;
        private const int LBS_USETABSTOPS = 0x0080;
        private const int LBS_NOINTEGRALHEIGHT = 0x0100;
        private const int LBS_MULTICOLUMN = 0x0200;
        private const int LBS_WANTKEYBOARDINPUT = 0x0400;
        private const int LBS_EXTENDEDSEL = 0x0800;
        private const int LBS_DISABLENOSCROLL = 0x1000;
        private const int LBS_NODATA = 0x2000;
        private const int LB_GETCOUNT = 0x018B;
        private const int LB_SETCOUNT = 0x01A7;
        
        public VirtualListBox()
        {
            InitializeComponent();
        }
    

        /// <summary>
        /// Sets up the <see cref="CreateParams" /> object to tell 
        /// Windows how the ListBox control should be created.  In 
        /// this instance the default configuration is modified to 
        /// remove <c>LBS_HASSTRINGS</c> and <c>LBS_SORT</c> 
        /// styles and to add <c>LBS_NODATA</c>and LBS_OWNERDRAWFIXED 
        /// styles. This converts the ListBox into a Virtual ListBox.
        /// </summary>
        protected override System.Windows.Forms.CreateParams CreateParams
        {
        get
        {
            CreateParams defParams = base.CreateParams;
            defParams.Style = defParams.Style & ~LBS_HASSTRINGS;
            defParams.Style = defParams.Style & ~LBS_SORT;
            defParams.Style = defParams.Style | 
                LBS_OWNERDRAWFIXED | LBS_NODATA;
            return defParams;
        }
        }
    
        [DllImport("user32", CharSet = CharSet.Auto)]
        private extern static int SendMessage(
        IntPtr hWnd, int msg, int wParam, IntPtr lParam);
    
        /// <summary>
        /// Gets or sets the number of virtual items in the ListBox.
        /// </summary>
        public int Count
        {
        get
        {
            return SendMessage(this.Handle, 
                LB_GETCOUNT, 0, IntPtr.Zero);
        }
        set
        {
            SendMessage(this.Handle, 
                 LB_SETCOUNT, value, IntPtr.Zero);
        }    
        }
    
        /// <summary>
        /// Throws an exception.  All the items for a Virtual ListBox 
        /// are externally managed.
        /// </summary>
        /// <remarks>The selected index can be obtained using 
        /// the <see cref="SelectedIndex"/> and
        /// <see cref="SelectedIndices"/> properties.
        /// </remarks>
        [BrowsableAttribute(false)]
        public new SelectedObjectCollection SelectedItems
        {
            get
            {
                throw new InvalidOperationException("A Virtual ListBox does not have a SelectedObject collection");
            }
        }
    
        /// <summary>
        /// Gets/sets the selected index in the control.  If the 
        /// control has the multi-select style, then the first 
        /// selected item is returned.
        /// </summary>
        public new int SelectedIndex
        {
            get
            {
            int selIndex = -1;
            if (SelectionMode == SelectionMode.One)
            {
                selIndex = SendMessage(this.Handle, 
                    LB_GETCURSEL, 0, IntPtr.Zero);
            }         
            else if ((SelectionMode == SelectionMode.MultiExtended) || 
                (SelectionMode == SelectionMode.MultiSimple))
            {
                int selCount = SendMessage(this.Handle, 
                    LB_GETSELCOUNT, 0, IntPtr.Zero);
                if (selCount > 0)
                {
                    IntPtr buf = Marshal.AllocCoTaskMem(4);
                    SendMessage(this.Handle, LB_GETSELITEMS, 1, buf);
                    selIndex = Marshal.ReadInt32(buf);
                    Marshal.FreeCoTaskMem(buf);
                }
            }
            return selIndex;
            }
            set
            {
            if (SelectionMode == SelectionMode.One)
            {
                SendMessage(this.Handle, 
                    LB_SETCURSEL, value, IntPtr.Zero);
            }
            else if ((SelectionMode == SelectionMode.MultiExtended) || 
                (SelectionMode == SelectionMode.MultiSimple))
            {
                // clear any existing selection:
                SendMessage(this.Handle, LB_SETSEL, 0, new IntPtr(-1));
                // set the requested selection
                SendMessage(this.Handle, LB_SETSEL, 1, (IntPtr) value);
            }
        }   
    }      
  }
}