How To Perform Paging with the DataGrid Windows Control by Using Visual Basic .NET (305271)

SUMMARY

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

The code samples in this article make use of DataSet objects. In ADO.NET, DataSet objects are filled in a single operation and reside in memory all of the time. If you are working with a large DataSet, this article describes how to display the data in chunks or pages programmatically.

This technique has some limitations. Please see the Troubleshooting section for more information.

back to the top

Requirements

• Microsoft Visual Basic .NET
• Microsoft SQL Server Northwind sample database

back to the top

Steps to Add Paging to a DataGrid Windows Control

When you page a DataGrid, you display data in page-size "chunks," that is, one page of records at a time. The sample code to follow copies the DataRow objects for each page from the DataSet in memory to a temporary table. The temporary table is then bound to the DataGrid control.

1. Open a new Visual Basic .NET Windows Application. Form1 is created by default.
2. Add DataGrid control, and set its ReadOnly property to True.
3. Place the following additional controls on Form1, and set their properties as shown below:

   Control	Name Property	Text Property
   Button	btnFirstPage	First Page
   Button	btnNextPage	Next Page
   TextBox	txtDisplayPageNo
   Button	btnPreviousPage	Previous Page
   Button	btnLastPage	Last Page
   TextBox	txtPageSize	5
   Button	btnFillGrid	Fill Grid

   
   
4. Copy and paste the following code into Form1's General Declaration section:

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

5. Copy and paste the following code before the "Windows Form Designer generated code" region to declare form-level variables for 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. Delete the following auto-generated code for Load event of Form1.

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

7. Copy and paste the following code after the "Windows Form Designer generated code" region:

   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. Modify the ConnectionString parameter in the code so that it points to an existing instance of the Northwind database.
9. Press the F5 key to build and run the project.
10. By default, the Page Size is set to 5 records, so you can change it in the text box.
11. Click Fill Grid. Notice that the Grid is filled with 5 records.
12. Click First Page, Next Page, Previous Page, and Last Page to browse between pages.

back to the top

Troubleshooting

• This technique only works for read-only DataGrid controls. When you import a row to a temporary DataTable object, you make a copy. Thus, changes that you make will not be saved to the main table.
• This technique does not work (and neither does a collection or an array) if you want the user to be able to navigate to child records through a DataRelation object or if you have records that are linked in a parent-child relation that appear on the form at the same time.

back to the top