One of the typical problems in workflow development is task
deletion. Usually users that interact with the task, have contribute permission
to the task which means they can simply delete the tasks that are created as a
part of workflow processing. Deleting a task can mess up the workflow and we may
need to handle it as a part of the workflow. But how can we stop the users from
deleting tasks? The solution is very simple. Item event handlers in MOSS/WSS
2007 can easily take care of this case. Item event handlers are events that are
registered to a list and mapped to a dll that is already deployed to GAC. When
an event (insert, delete and update) happens the event handler fires and execute
the code that can do something in response or may even cancel the event trigger
progression. This is exactly our scenario. We need to build an event handler
that when a user tries to delete a task, it checks the task status. If the
status is not "Completed" then in cancels the deletion and
displays an error message. To implement this simply create a class library
project in Visual Studio .NET and make a reference to Windows SharePoint
Services Library. Then add the following code. Inline code description is
included.
using
System;
using
System.Collections.Generic;
using
System.Text;
using
Microsoft.SharePoint;
namespace
StopActiveTaskDelete
{
//Inhertit your class from SPItemEventReceiver
public class
CActiveTasksDelete:
SPItemEventReceiver
{
// Override the ItemDeleting function. You
will find also ItemDeleted
// function that fires when the item is
deleted. For your scenario we
// need ItemDeleting to stop the delete
process before it is complete.
public
override void ItemDeleting(SPItemEventProperties
properties)
{
//Built in call to the initial definition
base.ItemDeleting(properties);
// Get reference to the current item being
deleted
SPListItem myItem =
properties.ListItem;
// Read the status field of the item being
deleted
String taskStatus =
myItem["Status"].ToString();
// Is the task status is Complete it is not active
task any more
// Otherwise we cancel the deletion
if (taskStatus !=
"Completed")
{
// This is the message that we'd like
to show to the user
// if he/she tries to delete an
active task
properties.ErrorMessage =
"This task is still in progress and cannot be deleted";
// This line actually cancels the
delete
properties.Cancel = true;
}
}
}
}
Sign the assembly with a strong name key and deploy it to the global assembly
cache. Now all you need to do is to introduce the this assembly to a task list
in SharePoint. There are different ways of doing it, but the simplest way is
using a simple consol application to do so.
Your script should look like this:
using
System;
using
System.Collections.Generic;
using
System.Text;
using
Microsoft.SharePoint;
namespace
RegsiterEventReceiver
{
class Program
{
static void
Main(string[] args)
{
// Get reference to the the site that
containd your task list
SPSite mySite =
new SPSite("http://sharepointSiteURL");
SPWeb myWeb = mySite.OpenWeb();
// Get the reference to your task list
SPList myList =
myWeb.Lists["Tasks"];
myList.EventReceivers.Add(SPEventReceiverType.ItemDeleting,
"StopActiveTaskDelete,
Version=1.0.0.0, Culture=neutral" +
//Replace this key with your own
assembly publick key token
", PublicKeyToken=8a1a592e4ca85c4c",
"StopActiveTaskDelete.CActiveTasksDelete");
// Don't forget to update the list
myList.Update();
// Make sure you add this life to feel
good after your
// Solution is deployed
successfully
Console.WriteLine("Haha,
done!");
}
}
}
Now go to the
SharePoint Site and try to delete an incomplete task. You will get this error
page.
And this code will protect active tasks from deletion happily ever
after.
Cheers
Alireza