CustomDataGrid

    [ToolboxBitmap(typeof(DataGrid))]
    public partial class CustomDataGrid : DataGrid
    {
        private DataSet _myDataSource=null; //数据源
        private int _columnNum = 10; //每行显示的列数
        private static int pageNum = 1;


        private int CAPTIONHEIGHT = 21;
        private int BORDERWIDTH = 2;

        

        [DefaultValue(typeof(Int16), "10"), Description("每页显示的列数")]
        public int ColumnNum
        {
            get { return _columnNum; }
            set
            { 
                _columnNum = value;
                base.Invalidate();
            }
        }

        /// <summary>
        /// 自定义数据源
        /// </summary>
        public DataSet MyDataSource
        {
            get { return _myDataSource; }
            set 
            { 
                _myDataSource = value;
                this.DataSource = getTopNum(MyDataSource, ColumnNum * pageNum);
            }
        }

        

        public CustomDataGrid()
        {
            InitializeComponent();
            pageNum = 1;
            this.VertScrollBar.Visible = true;
            this.VertScrollBar.VisibleChanged += new EventHandler(ShowScrollBars); 
            this.VertScrollBar.Scroll+=new ScrollEventHandler(VertScrollBar_Scroll);
        }
        /// <summary>
        /// 滚动条事件
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void VertScrollBar_Scroll(object sender, ScrollEventArgs e)
        {
            if (MyDataSource != null)
            {
                if (e.NewValue > e.OldValue)
                {
                    pageNum++;
                    int num = ColumnNum * pageNum; //将要显示的条数
                    this.DataSource = null;
                    this.DataSource = getTopNum(MyDataSource, num);
                }
            }
        }
        /// <summary>
        /// 始终显示滚动条
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void ShowScrollBars(object sender, EventArgs e)
        {
            if (!this.VertScrollBar.Visible)
            {
                int width = this.VertScrollBar.Width;
                this.VertScrollBar.Location = new Point(this.ClientRectangle.Width - width - BORDERWIDTH, CAPTIONHEIGHT);
                this.VertScrollBar.Size = new Size(width, this.ClientRectangle.Height - CAPTIONHEIGHT - BORDERWIDTH);
                this.VertScrollBar.Show();
            }
        } 
        protected override void OnPaint(PaintEventArgs pe)
        {
            base.OnPaint(pe);
        }

        /// <summary>
        /// 动态的加载数据
        /// </summary>
        /// <param name="dataSource"></param>
        /// <param name="num"></param>
        /// <returns></returns>
        private DataTable getTopNum(DataSet dataSource, int num)
        {
            //this.
            if (num <= 0)
            {
                num = 10;//默认显示的条数
            }
            if (dataSource != null)
            {
                DataTable dataTable = new DataTable();
                DataTable table = dataSource.Tables[0];
                dataTable = ((from s in table.AsEnumerable() select s).Take(num)).CopyToDataTable();
                return dataTable;
            }
            else
            {
                return null;
            }
        }
        
    }