Microsoft SharePoint 2007 Technologies

17.2 Working with Events 533

Chapter 17

17.2 Working with Events

So now that we understand the type of event handlers that can be written,

let’s look at the actual process involved in creating and implementing an

event handler. The process in and of itself is quite straightforward and

involves three main stages: creation, deployment, and registration. The cre-

ation stage typically involves a developer creating an event handler assembly

that overrides the relevant event receiver methods. Once the assembly file has

been created, the developer can then package the assembly into a solution file

for the administrator to deploy on the appropriate Web servers. Once the

event handler is installed all that remains is for the event receivers to be regis-

tered with the appropriate SharePoint containers, such as a specific Web site

or a set of document libraries. To make the administrator’s life a lot easier,

and make the deployment process more streamlined, the developer can

include the registration process as part of the solution package.

The following section will take you through the process of implement-

ing a simple event handler that prevents items from being deleted from a

specific document library within a specific SharePoint Web site, regardless

of the user’s permission level.

17.2.1 Creating an Event Handler

The first step in the process is to create the event handler. The event handler

needs to be able to trap when a user attempts to delete a Web site within our

site collection; therefore, our event handler will need to inherit the

SPItemEventReceiver class and override the ItemDeleting method. To

follow along with the example, create a new C# Class Library project in

Visual Studio 2005, add a reference to

Microsoft.SharePoint, and add

the code listed in Figure 17.14. Once the code is entered, you can build the

project assembly.

Figure 17.14

ItemDeleting code.

534 17.2 Working with Events

SharePoint event handler assemblies must be strongly named and

deployed to the global assembly cache (GAC) before they can be used. As a

quick refresh, you can use the Strong Name Tool (sn.exe) to strongly name

your assembly or, alternatively, use the Signing tab available in Visual Studio

2005. If you are using the Signing tab, then your assembly is strongly named

as part of the build process.

At this stage the assembly file has been created; next we need to deploy

the file and register the event handler.

17.2.2 Deploying an Event Handler

Once again, event handler assemblies must be strongly named and

deployed to the GAC before they can be used. A very simple way to deploy

an assembly file to the GAC is to drag the strongly named .dll build file

from its project directory and drop it into the GAC, which is usually

located in the

\WINDOWS\assembly directory. This particular method of

deployment is fine for demonstration purposes, but when it comes to pro-

duction, the recommended method of deploying event handlers is to lever-

age the Solution Deployment framework. Doing so allows you to inherit

all the benefits of the framework, such as providing a central place for

deployment to all appropriate Web applications and Web front-end servers,

providing a central place for upgrades and for retracting the solution, and

being able to package the deployment and registration of the event handler.

Chapter 11, Introduction to SharePoint Development, explains the steps

involved in packaging and deploying a Web Part solution; since an event

handler is just a .dll, the same technique can the applied to deploy the

event handler to the GAC of all the appropriate Web front-end servers.

As previously mentioned, the registration of the event handler can be

incorporated into the deployment process by including a registration

mechanism in the solution deployment files. For example, the solution

deployment package could include a Feature that, upon activation, would

register the event handlers to all the relevant SharePoint containers; upon

deactivation, the same Feature would unregister the event handlers. More

information on how to create Features that handle activation events can be

found in Chapter 16, Features.

17.2.3 Registering an Event Handler

The registration of an event handler refers to the process that takes a specific

method that a custom event handler overrides and binds it to a SharePoint

object such as a list, document library, or even a content type. For example,

in our scenario we can bind the

ItemDeleting method from our assembly to

a specific SharePoint list. If you examine the object model you will see that