Library tutorials & articles
Object-Oriented ASP.NET
- Introduction
- Real World Example
- A Better Way
- Putting it All Together
Putting it All Together
Now comes the beautiful part. Once we have created our derived DataGrid class
called ConfirmDelDataGrid, using it and leveraging its new built-in functionality
is a snap. First, add a @Register tag on the .aspx page to register the datagrid
class and use it rather than <asp:DataGrid>:
<%@ Register tagprefix="dg" Namespace="ooaspnet" Assembly="ooaspnet" %>
<
!-- (page layout & design here)... -->
<
dg:ConfirmDelDataGrid id="grid" runat="server" ..... ><dg:ConfirmDelDataGrid>
You'll also need to set the code-behind in your .cs file to use the new derived class: protected ConfirmDelDataGrid grid;
private void Page_Load(object sender, System.EventArgs e)
{
if (!IsPostBack)
{
grid.ConfirmOnDelete = true;
grid.DataSource = new string[4] { "red", "green", "blue", "purple" };
grid.DataBind();
}
}
This is as simple as it gets. We have a new DataGrid subclass with a property that lets us automatically add confirmation message boxes, without knowing (or caring) at the Page level how it works.
Also, if we ever decide to improve the code for attaching the javascript, we can just modify the code inside the ConfirmDelDataGrid class once. Every page that uses this class will automatically benefit from the changes.
Conclusion
Programming ASP.NET allows us to take advantage of the powerful features of the underlying languages that we use. We can use object-oriented design features such as inheritance and encapsulation to develop re-usable classes that work autonomously and do not require glue code on the Page objects.
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I am getting as error message of
C:\Program Files\ASP.NET Starter Kits\ASP.NET Portal (CSSDK)\PortalCSSDK\RegDataGrid.cs(20): The type or namespace name 'DataSource' could not be found (are you missing a using directive or an assembly reference?)
and
C:\Program Files\ASP.NET Starter Kits\ASP.NET Portal (CSSDK)\PortalCSSDK\RegDataGrid.cs(54): The type or namespace name 'DataGridItemEventArgs' could not be found (are you missing a using directive or an assembly reference?)
when running the code. What am I missing?
Here is the code I am running.
using System;
namespace ASPNET.StarterKit.Portal
{
/// <summary>
///
/// </summary>
public class RegDataGrid : System.Web.UI.WebControls.DataGrid
{
public RegDataGrid()
{
//
// TODO: Add constructor logic here
//
}
// Class member that stores the index of the "Delete" column of this grid
protected int delcol = -1;
protected override ArrayList CreateColumnSet(PagedDataSource dataSource, bool useDataSource)
{
// Let the DataGrid create the columns
ArrayList list = base.CreateColumnSet (dataSource, useDataSource);
// Examine the columns
delcol=0;
foreach (DataGridColumn col in list)
{
// If this column is the "Delete" button command column...
if ((col is ButtonColumn) && (((ButtonColumn)col).CommandName == "Delete"))
{
// Found it
break;
}
delcol++;
}
// If we did not find a delete column, invalidate the index
if (delcol == list.Count) delcol = -1;
// Done
return list;
}
// Property to enable/disable deletion confirmation
protected bool confirmdel = true;
public bool ConfirmOnDelete
{
get { return confirmdel; }
set { confirmdel = value; }
}
protected override void OnItemDataBound(DataGridItemEventArgs e)
{
// Create it first in the DataGrid
base.OnItemDataBound (e);
// Attach javascript confirmation to the delete button
if ((confirmdel) && (delcol != -1))
{
e.Item.Cells[delcol].Attributes.Add("onclick", "return confirm('Are you sure?')");
}
}
}
}
Mick:
shoot me an email at elliotmrodriguezathotmaildotcom and I will send you the class file. Perhaps we can work together on this.
Oddly enough, when I compile (without errors) and set a reference to the file in my web page, the grid never gets displayed. I've stepped through the code on the webpage that sets its properties, and they work fine; Intellisense shows my properties for the class, so I know its being seen, but none of the events in the class itself get called. I am perplexed.
Greg Ennis, can you also help?
Hi Elliot,
Is there any chance that you can show me the code for the derived datagrid in VB.net.
Im having trouble creating it myself. Im new to this subclassing stuff.
Thank you
Mick Lennon
Louth
Ireland
You have to add the class manually as a generic class, then use the Inherits statement
Public Class DeleteDataGrid ' or whatever you want to call it
Inherits System.Web.UI.WebControls.DataGrid
Hitting ENTER after the Inherits statement will make the stubs appear automagically for both CreateControlHierarchy and PrepareControlHierarchy. OnItemDataBound, however, does not show up; you will have to add the function signature yourself.
HTH
great article. I was able to implement the grid in VB.NET quite easily, and I plan on extending it in similar fashion to create DataGrids with selectable rows. Thanks Greg!
I'm using VB.NET 2003 and I don't see the "Add" option when I right click in the Class view either.
Great article, but am I missing something. I go into Class view, but I get no "Add" option when I right-click on the project. This is an ASP.Net (VB.Net) project, so is it the case that this is not available in ASP.Net projects?
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