How To Perform Paging with the DataGrid Windows Control by Using Visual Basic .NET

TheDataGridWeb control has built-in Automatic or Custom Paging functionalities; however, theDataGridWindows control lacks these features. This article demonstrates how to build a simple paging mechanism for theDataGridWindows control.

The code samples in this article make use ofDataSet???????? ??? In ADO.NET,DataSet???????? ???? ??? ???????? ??? ??? ?? ?????? ??? ????? ??? ???? ??? ?? ???? ??? ?? ??? ??? ?? ??? ???DataSet, ?? ???? ????? ?? ?? ???? ??? ??? ???? ????????? ???? ?? ??? ?? ????????? ?????? ??????

?? ????? ?? ??? ?????? ??? ??? ????? ??????????? ?????????? ??????? ?? ??? ????

??????????

• Microsoft Visual Basic .NET
• Microsoft SQL Server ????????? ????? ???????

??? DataGrid Windows ?? ???????? ???? ?? ??? ?????? ?????? ???? ?? ??? ???

?? ?? ????? ??DataGrid, ?????-???? ??? "???," ??, ???? ?? ??? ?? ??? ??? ???????? ?? ???? ?? ????????? ???? ????????? ?? ???? ???? ?? ??? ????? ???DataRow???????? ????? ?? ?? ??? ????????DataSet??? ??? ??????? ?????? ?? ??? ??????? ??????? ?????? ??? ???? ?? ??? ????? ??DataGrid???????? ???

1. ??? Visual Basic .NET Windows ????????? ?? ?????? Form1 ???????? ??? ?? ???? ??..
2. addDataGrid??? ????, ?? ???????? ????ReadOnly???? ?? ??? ???True.
3. ????? ???????? ???????? Form1 ?? ????, ?? ???? ????? ?? ?? ??? ??? ???? ??? ??? ????:
   ?? ?????? ?? ??????? ?????? ?????? ?? ??????? ????

   ????????	??? ???	??? ?? ???
   ???	btnFirstPage	????? ?????
   ???	btnNextPage	???? ?????
   ??? ?????	txtDisplayPageNo
   ???	btnPreviousPage	????? ?????
   ???	btnLastPage	????? ?????
   ??? ?????	txtPageSize	5
   ???	btnFillGrid	????? ????

   
   
4. ?? ????????? ?????, ?? Form1 ?? ??????? Declaration ?????? ??? ????? ??? ???????:

   Imports System
   Imports System.Data
   Imports System.Data.SqlClient
   					

5. ?? ????????? ????? ?? ????? ??? ???????????"Windows ??????? ??????? ??? ????? ???? ???" ??????? Form1 ?? ??? ???????-???? ?? ?? ????? ???? ?? ???:

       Private da As SqlDataAdapter
       Private ds As DataSet
       Private dtSource As DataTable
       Private PageCount As Integer
       Private maxRec As Integer
       Private pageSize As Integer
       Private currentPage As Integer
       Private recNo As Integer
   					

6. ????? ????: ????? ??? ?? ??? ???????? ????Form1 ??????

   Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) _
     Handles MyBase.Load
   
   End Sub
   					

7. ?? ????????? ????? ?? ????? ??? ??????????? ???"Windows ??????? ??????? ??? ????? ???? ???" ??????? ???:

   Private Sub Form1_Load(ByVal sender As System.Object, _
       ByVal e As System.EventArgs) Handles MyBase.Load
   
       'Open Connection.
       Dim conn As SqlConnection = New SqlConnection( _ 
   "Server=(local)\netsdk;uid=sa;pwd=;database=northwind")
   
       'Set the DataAdapter's query.
       da = New SqlDataAdapter("select * from customers", conn)
       ds = New DataSet()
   
       ' Fill the DataSet.
       da.Fill(ds, "customers")
   
       ' Set the source table.
       dtSource = ds.Tables("customers")
   
   End Sub
   
   Private Sub btnNextPage_Click(ByVal sender As System.Object, _ 
       ByVal e As System.EventArgs) Handles btnNextPage.Click
   
       'If the user did not click the "Fill Grid" button then Return
       If Not CheckFillButton() Then Return
   
       'Check if the user clicked the "Fill Grid" button.
       If pageSize = 0 Then
           MessageBox.Show("Set the Page Size, and then click the ""Fill Grid"" button!")
           Return
       End If
   
       currentPage = currentPage + 1
   
       If currentPage > PageCount Then
           currentPage = PageCount
   
           'Check if you are already at the last page.
           If recNo = maxRec Then
               MessageBox.Show("You are at the Last Page!")
               Return
           End If
       End If
   
       LoadPage()
   End Sub
   
   Private Sub btnPreviousPage_Click(ByVal sender As System.Object, _ 
       ByVal e As System.EventArgs) Handles btnPreviousPage.Click
   
       If Not CheckFillButton() Then Return
   
       If currentPage = PageCount Then
           recNo = pageSize * (currentPage - 2)
       End If
   
       currentPage = currentPage - 1
   
       'Check if you are already at the first page.
       If currentPage < 1 Then
           MessageBox.Show("You are at the First Page!")
           currentPage = 1
           Return
       Else
           recNo = pageSize * (currentPage - 1)
       End If
   
       LoadPage()
   End Sub
   
   Private Sub LoadPage()
       Dim i As Integer
       Dim startRec As Integer
       Dim endRec As Integer
       Dim dtTemp As DataTable
       Dim dr As DataRow
   
       'Duplicate or clone the source table to create the temporary table.
       dtTemp = dtSource.Clone
   
       If currentPage = PageCount Then
           endRec = maxRec
       Else
           endRec = pageSize * currentPage
       End If
   
       startRec = recNo
   
       'Copy the rows from the source table to fill the temporary table.
       For i = startRec To endRec - 1
           dtTemp.ImportRow(dtSource.Rows(i))
           recNo = recNo + 1
       Next
   
       DataGrid1.DataSource = dtTemp
       DisplayPageInfo()
   
   End Sub
   
   Private Sub btnFirstPage_Click(ByVal sender As System.Object, _ 
       ByVal e As System.EventArgs) Handles btnFirstPage.Click
   
       If Not CheckFillButton() Then Return
   
       ' Check if you are already at the first page.
       If currentPage = 1 Then
           MessageBox.Show("You are at the First Page!")
           Return
       End If
   
       currentPage = 1
       recNo = 0
   
       LoadPage()
   
   End Sub
   
   Private Sub btnLastPage_Click(ByVal sender As System.Object, _ 
       ByVal e As System.EventArgs) Handles btnLastPage.Click
   
       If Not CheckFillButton() Then Return
   
       ' Check if you are already at the last page.
       If recNo = maxRec Then
           MessageBox.Show("You are at the Last Page!")
           Return
       End If
   
       currentPage = PageCount
   
       recNo = pageSize * (currentPage - 1)
   
       LoadPage()
   
   End Sub
   
   Private Sub DisplayPageInfo()
       txtDisplayPageNo.Text = "Page " & currentPage.ToString & "/ " & PageCount.ToString
   End Sub
   
   Private Sub btnFillGrid_Click(ByVal sender As System.Object, _ 
       ByVal e As System.EventArgs) Handles btnFillGrid.Click
   
       'Set the start and max records. 
       pageSize = txtPageSize.Text
       maxRec = dtSource.Rows.Count
       PageCount = maxRec \ pageSize
   
       ' Adjust the page number if the last page contains a partial page.
       If (maxRec Mod pageSize) > 0 Then
           PageCount = PageCount + 1
       End If
   
       'Initial seeings
       currentPage = 1
       recNo = 0
   
       ' Display the content of the current page.
       LoadPage()
   
   End Sub
   
   Private Function CheckFillButton() As Boolean
   
       'Check if the user clicks the "Fill Grid" button.
       If pageSize = 0 Then
           MessageBox.Show("Set the Page Size, and then click the ""Fill Grid"" button!")
           CheckFillButton = False
       Else
           CheckFillButton = True
       End If
   End Function
   					

8. ??????? ????ConnectionString???????? ??? ????? ?? it ????????? ??????? ??? ?? ?????? ??????? ?? ????? ???? ???
9. ????? ?? ????????? ?? ????? ?? ??? F5 ????? ??????
10. ???????? ??? ??, ????? ???? ??? ??, 5 ??????? ???? ?? ??? ???? ?? ??? ????? ??? ??? ??? ???? ????
11. ????? ????,????? ????. ????? ??? ?? ????? 5 ??????? ?? ??? ???
12. ????? ????,????? ?????,???? ?????,????? ?????, ??????? ???????????? ?? ??? ??????? ???? ???? ?? ????

?????? ??????

• ???? ?? ??? ?? ????? ???? ??? ???? ???? -DataGrid???????? ??? ?? ?? ???? ?????? ?? ???? ?? ???????DataTable????????, ?? ?? ????????? ?????? ??????, ?? ?? ???????? ????? ???? ?????? ????? ?????? ?? ????
• ?? ????? ?? ??? ???? ???? ?? (?? neither ?????? ?? ???? ??) ??? ?? ?????????? ?????? ?????? ?????? ??? ??????? ???? ??? ????? ???? ?? ??? ???DataRelation???????? ?? ??? ???? ??? ?????? ??? ?? ?????? ?????? relation ?? ???? ?? ?? ??? ?? ??????? ?? ?? ?? ??? ??? ??? ???? ????

ADO.NET ?? ???? ??? ???? ??????? ?? ??? ????? ????? MSDN ??? ????:???? ??????? ?? ???, Microsoft .NET Framework SDK ????? ????????: