Library tutorials & articles
Object-Oriented ASP.NET
- Introduction
- Real World Example
- A Better Way
- Putting it All Together
Real World Example
For this example I will be using a common scenario developers encounter with the DataGrid. The DataGrid gives us some powerful pre-built column objects, including command columns which allow the user to press buttons (or links) to select, edit, or delete items in the grid. Imagine you are writing a web form which uses a DataGrid having a "Delete" column, and you want to make the user confirm the deletion before actually deleting the item.
This is accomplished by using some client-side javascript to invoke the confirm function in the onclick handler:
<... onclick="return confirm('Are you sure?');" >
The way that you attach this code to the Delete button is to add to the item's Attributes collection when the item is created:
Control.Attributes.Add("onclick", "return
confirm('Are you sure?')");
You will typically find code like this in the Page class which is handling
the OnItemCreated event of the grid. It usually goes something like this:
private void InitializeComponent()
{
this.grid.ItemCreated += new System.Web.UI.WebControls.DataGridItemEventHandler(this.OnItemCreated);
// ...(other handlers)...
}
private void OnItemCreated(object sender, System.Web.UI.WebControls.DataGridItemEventArgs
e)
{
if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem)
{
Button btn = e.Item.FindControl("delbutton");
btn.Attributes.Add("onclick", "return confirm('Are you sure?')");
}
}
I find this approach to be flawed for two reasons:
- Encapsulation is being violated. Why is it the job for the Page object to fiddle around with the internal attributes of the datagrid? It would be ideal if the page object could simply set a boolean property to enable the confirmation message box.
- If you want to have delete confirmations for all 5 grids in all 5 pages
of your application, you are going to have to repeat at least some of this
code 5 times in your page classes. You can try to work around this by sharing
some common code, but you still have to hook up an event handler for each grid
in each page's
InitializeComponent.
Related articles
Related discussion
-
Very Urgent regarding deleting the images from a folder
by rameshbandi (2 replies)
-
New style of Javascript used in extenders.
by mittalpa (0 replies)
-
roulette game in windows application
by pdhanik (1 replies)
-
Chart insertation in a windows form...
by pdhanik (1 replies)
-
Bookstore in trieste
by atmir04041987 (1 replies)
Related podcasts
-
StackOverflow uses ASP.NET MVC - Jeff Atwood and his technical team
Scott chats with Jeff Atwood of CodingHorror.com and most recently, StackOverflow.com. Jeff and Joel Spolsky and their technical team have created a new class of application using ASP.NET MVC. What works, what doesn't, and how did it all go down?
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?
This thread is for discussions of Object-Oriented ASP.NET.