Tùy chỉnh paging trong Control GridView ASP.NET

protected int pageIndex = 1;
protected int pageCount = 0;
protected int rowCount = 0;
private const int CONST_PAGE_SIZE = 5;

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        BindData();
        //based on the row count & page size, calculate page count
        pageCount = CalcPageCount(rowCount);
        ViewState["PageCount"] = pageCount;
        RefreshPageButtons();
    }
    else
    {
        if (ViewState["PageIndex"] != null)
            pageIndex = Convert.ToInt32(ViewState["PageIndex"]);
        if (ViewState["PageCount"] != null)
            pageCount = Convert.ToInt32(ViewState["PageCount"]);
    }
}
private int CalcPageCount(int totalRows)
{
    return (int)(totalRows / CONST_PAGE_SIZE);           
}

CREATE procedure [dbo].[sp_Products_Get]
 (    
     @PageSize int,
     @PageIndex int,
     @RecordCount int output
 )
 AS
 BEGIN   
 DECLARE @tblProduct TABLE(
  ProductID int not null,
  Name varchar(255) ,
  ProductNumber varchar(255),
  ListPrice decimal
 )
 DECLARE @index int
 SET @ index =@PageSize*(@PageIndex - 1) 
 INSERT INTO @tblProduct (ProductID, Name,ProductNumber,ListPrice)
 SELECT ProductID, Name,ProductNumber,ListPrice FROM tblProduct
  
 SELECT @RecordCount=Count(*) FROM @tblProduct
  
 SET ROWCOUNT @PageSize
 SELECT ProductID, Name,ProductNumber,ListPrice FROM  @tblProduct WHERE
ProductID > @ index
 SET ROWCOUNT 0 
 END

private void BindData()
{
    DataSet dsProducts = RetrieveProducts();
    //Bind the grid view
    gvProducts.DataSource = dsProducts;
    gvProducts.DataBind();         
}
private DataSet RetrieveProducts()
{
    if (ViewState["Products"] != null)
        return (DataSet)ViewState["Products"];
    //fetch the connection string from web.config
    string connString =
ConfigurationManager.ConnectionStrings["Sql"].ConnectionString;
    DataSet dsProducts = new DataSet();
    //Open SQL Connection
    using (SqlConnection conn = new SqlConnection(connString))
    {
        conn.Open();
        //Initialize command object
        using (SqlCommand cmd = new SqlCommand("sp_Products_Get", conn))
        {
            cmd.CommandType = CommandType.StoredProcedure;
            //add input parameters to the SP
            cmd.Parameters.AddWithValue("@PageIndex",pageIndex);
            cmd.Parameters.AddWithValue("@PageSize", CONST_PAGE_SIZE);
            //add output parameters
            cmd.Parameters.Add("@RecordCount", SqlDbType.Int);
            cmd.Parameters["@RecordCount"].Direction =
ParameterDirection.Output;
            SqlDataAdapter adapter = new SqlDataAdapter(cmd);
            //Fill the result set
            adapter.Fill(dsProducts);
            //get the output value
            rowCount = (int)cmd.Parameters["@RecordCount"].Value;
        }
    }
    return dsProducts;
}

protected void PageChangeEventHandler(object sender, CommandEventArgs e)
{
    switch (e.CommandArgument.ToString())
    {
        case "First":
            pageIndex = 1;
            break;
        case "Prev":
            pageIndex = pageIndex - 1;
            break;
        case "Next":
            pageIndex = pageIndex + 1;
            break;
        case "Last":
            pageIndex = pageCount;
            break;
    }
    //set the latest page index back to view state
    ViewState["PageIndex"] = pageIndex;
    //fetch the latest batch of products
    BindData();
    //enable/disable page buttons based on current page index
    RefreshPageButtons();
}
private void RefreshPageButtons()
{
    btnFirst.Enabled = true;
    btnPrevious.Enabled = true;
    btnNext.Enabled = true;
    btnLast.Enabled = true;
    //if this is the first page, disable previous page
    if (pageIndex == 1)
    {
        btnPrevious.Enabled = false;
        btnFirst.Enabled = false;
        //if the page count is more than 1, enable next button               
        if (pageCount <= 0)
            btnNext.Enabled = false;               
    }
    else
    {               
        if (pageIndex == pageCount)
        {
            btnNext.Enabled = false;
            btnLast.Enabled = false;
        }              
    }
}

CREATE TABLE [dbo].[tblProduct](
 [ProductID] [int] IDENTITY(1,1) NOT NULL,
 [Name] [varchar](255) NOT NULL,
 [ProductNumber] [varchar](255) NOT NULL,
 [ListPrice] [numeric](9, 2) NOT NULL,
 CONSTRAINT [PK_tblProduct_ProductID] PRIMARY KEY CLUSTERED
(
 [ProductID] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF,
IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]
 
GO
 
DECLARE @COUNTER INT, @productname VARCHAR(255),
 @productnumber VARCHAR(255), @listprice DECIMAL
SET @COUNTER = 0
SET @productname = 'product name '
SET @productnumber = 'product number '
SET @listprice = 500
WHILE(@COUNTER <= 20)
BEGIN
 SET @listprice= @listprice + 100
 INSERT INTO [dbo].[tblProduct]
     VALUES
           (@productname + convert(VARCHAR, @COUNTER)
           ,@productnumber + convert(VARCHAR, @COUNTER)
           ,@listprice)
 SET @COUNTER = @COUNTER + 1          
END