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 create a simple paging mechanism for the
DataGrid Windows control.
The code samples in this article use
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 sample uses the Customers table from
the Microsoft SQL Server Northwind database as the database backend. If you
connect to any other database or to a different table, make sure that you
update the code accordingly.
This technique has some limitations. See
the
Troubleshooting section for more
information.
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Requirements
The following list outlines the recommended hardware, software,
network infrastructure, and service packs that are required:
- Microsoft Windows 2000 Professional, Microsoft Windows 2000
Server, Microsoft Windows 2000 Advanced Server, Microsoft Windows NT 4.0 Server
or later
- Microsoft Visual Studio .NET
- Microsoft Visual J# .NET Beta 2
- Microsoft SQL Server 7.0 or later
This article assumes that you are familiar with the following
topics:
- Visual J# .NET
- ADO.NET fundamentals and syntax
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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.
- Open a new Visual J# .NET Windows Application
project.
- Add DataGrid control, and then set its ReadOnly property to True.
- Place the following additional controls on Form1, and set
their properties as follows:
|
| 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 |
| DataGrid | dataGrid1 | |
- In the Toolbox, click the Data tab.
- Double-click the SqlDataAdapter.
- Follow the instructions in the wizard.
- Right-click the SqlDataAdapter.
- Click to select Generate Data Set.
- Follow the instructions in the wizard.
- Open the properties for the SqlConnection. If you do not see the logon password after the user ID, type
it.
- Paste the following code in the top of the Form1 Code
window. Make sure that each namespace is referenced just one time. By default, System and System.Data may already be referenced.
import System.*;
- Paste the following code at the top of public class Form1 to declare form-level variables for Form1:
DataTable dtSource;
int PageCount;
int maxRec;
int pageSize;
int currentPage;
int recNo;
- Paste the following code in the constructor for the form:
// Standard Error Handling
try
{
// Get Data
dtSource = dataSet11.get_Tables ().get_Item("customers");
// Fill the DataSet
sqlDataAdapter1.Fill (dataSet11, "customers");
}
catch (Exception error)
{
// Display Error
MessageBox.Show ("Constructor failed with error: " + error);
}
- Paste the following code immediately after the static void Main method so that this code is form-level in scope:
// Get Data
private void LoadPage ()
{
// Local Declaration
int loop,
start,
stop,
rows;
DataTable dtTemp;
// Standard Error Handling
try
{
// Initialize
rows = dtSource.get_Rows ().get_Count ();
dtTemp = dtSource.Clone ();
// Error Checking
if (rows < 1)
{
MessageBox.Show ("No Data to Show", "Empty Table");
return;
}
// Set Loop Values
if (currentPage == PageCount) stop = maxRec;
else stop = pageSize * currentPage;
start = recNo;
// Transfer Data to Temporary Table
for (loop = start; loop < stop; loop ++)
{
dtTemp.ImportRow (dtSource.get_Rows ().get_Item(loop));
recNo ++;
}
// Show Data
dataGrid1.set_DataSource (dtTemp);
DisplayPageInfo ();
}
catch (Exception error)
{
MessageBox.Show ("LoadPage failed with error: " + error);
}
}
// Output Data
private void DisplayPageInfo()
{
txtDisplayPageNo.set_Text ("Page " + currentPage + " / " + PageCount);
}
// Notify to Fill Data Grid
private boolean CheckFillButton()
{
// Check if the user clicks the "Fill Grid" button.
if (pageSize == 0)
{
MessageBox.Show("Set the Page Size, and then click the Fill Grid button!");
return false;
}
else {return true;}
}
- Double-click the Fill Grid button to open the code window for btnFillGrid. Paste the following code in the btnFillGrid_Click event procedure:
// Set the start and max records.
pageSize = Convert.ToInt32(txtPageSize.get_Text ());
maxRec = dtSource.get_Rows ().get_Count ();
PageCount = maxRec / pageSize;
// Adjust the page number if the last page contains a partial
// page
if ((maxRec % pageSize) > 0) PageCount ++;
// Initial seeings
currentPage = 1;
recNo = 0;
// Display the content of the current page.
LoadPage();
- Double-click the First Page button to open the code window for btnFirstPage. Paste the following code in the btnFirstPage_Click event procedure:
// Verify Data
if (CheckFillButton() == false) return;
//Check if you are already at the first page.
if (currentPage == 1)
{
MessageBox.Show("You are at the First Page!");
return;
}
// Reset to First Page
currentPage = 1;
recNo = 0;
LoadPage();
- Double-click the Next Page button to open the code window for btnNextPage. Paste the following code in the btnNextPage_Click event procedure:
// If the user did not click the "Fill Grid" button, then
// return
if (CheckFillButton() == false) return;
// Check if the user clicks the "Fill Grid" button.
if (pageSize == 0)
{
MessageBox.Show("Set the Page Size, and then click the Fill Grid button!");
return;
}
// Check if you are already at the last page.
currentPage ++;
if (currentPage > PageCount)
{
currentPage = PageCount;
if (recNo == maxRec)
{
MessageBox.Show("You are at the Last Page!");
return;
}
}
LoadPage();
- Double-click the Previous Page button to open the code window for btnPreviousPage. Paste the following code in the btnPreviousPage_Click event procedure:
// Notify User
if (CheckFillButton() == false) return;
// Set Record Count
if (currentPage == PageCount)
recNo = pageSize * (currentPage - 2);
//Check if you are already at the first page.
currentPage --;
if (currentPage < 1)
{
MessageBox.Show("You are at the First Page!");
currentPage = 1;
return;
}
else {recNo = pageSize * (currentPage - 1);}
LoadPage();
- Double-click the Last Page button to open the code window for btnLastPage. Paste the following code in the btnLastPage_Click event procedure:
// Notify User
if (CheckFillButton() == false) return;
//Check if you are already at the last page.
if (recNo == maxRec)
{
MessageBox.Show("You are at the Last Page!");
return;
}
// Set Tracking
currentPage = PageCount;
recNo = pageSize * (currentPage - 1);
LoadPage();
- Press the F5 key to build and run the project.
- By default, the Page Size is set to 5 records. You can change this in the text
box.
- Click Fill Grid. Notice that the DataGrid is filled with 5 records.
- Click First Page, Next Page, Previous Page, and Last Page to view these pages.
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Troubleshooting
- This technique only works for read-only DataGrid controls. When you import a row to a temporary DataTable object, you make a copy. Therefore, changes that you make are not
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 locate child records through a DataRelation object or if you have records that are linked in a parent-child
relation and that appear on the form at the same time.
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