Creating SharePoint 2010 Event Receivers in Visual Studio 2010

转：http://msdn.microsoft.com/en-us/library/gg252010(v=office.14).aspx

Summary:  Learn how to create an event receiver for Microsoft SharePoint 2010 by using Microsoft Visual Studio 2010.

Applies to:  Microsoft SharePoint Foundation 2010 | Microsoft SharePoint Server 2010 | Microsoft Visual Studio 2010

Provided by:  Ben Hedges, Point8020

Microsoft Visual Studio 2010 provides a project type that enables you to build event receivers that perform actions before or after selected events on a Microsoft SharePoint 2010 site. This example shows how to add an event to the adding and updating actions
for custom list items.

This SharePoint Visual How To describes the following steps for creating and deploying an event receiver in Visual Studio 2010:

1. Overriding the itemAdding event and the itemUpdating event.

2. Verifying that the list to which the item is being added is the Open Position list.

3. Elevating permissions so that the code can access a secure site to retrieve approved job titles.

4. Comparing approved Job Titles with the title of a new item that is created in the
   Open Position list.

5. Canceling the event when the Job Title is not approved.

In this example, a secure subsite contains a list named Job Definitions that specifies allowed job titles for roles in the organization. Along with job titles, the list also contains confidential salary information for the job title and
is therefore secured from users. In the main site, a list named Open Positions tracks vacancies in the organization. You create two event receivers for the
itemAdding and itemUpdating events that verify that the title of the open position matches one of the approved titles in the
Job Definitions list.

Prerequisites

Before you start, create the subsite and lists that you will need.

To create the Job Definitions subsite

1. On the main site, on the Site Actions menu, click New Site.

2. In the New Site dialog box, click Blank Site.

3. On the right of the dialog box, click More Options.

4. In the Title box, type Job Definitions.

5. In the Web Site Address box, type JobDefinitions.

6. In the Permissions section, click Use Unique Permissions, and then click
   Create.

7. In the Visitors to this site section, select Use an existing group, and then select
   Team Site Owners. Click OK.

To create the Job Definitions list

1. In the Job Definitions site, create a custom list named
   Job Definitions with the following columns:

   • Title (Default column)

   • MinSalary (Currency)

   • MaxSalary (Currency)

   • Role Type (Choice: Permanent, Contract)

2. Add several jobs to this list. Note the titles that you specify for each job that you create because you will need them later.

To create the Open Positions list

• In the parent site, create a custom list named Open Positions with the following columns:

  • Title (Default column)

  • Location (Single line of text)

Creating an Event Receiver

Next, create an Event Receiver project in Visual Studio 2010, and add code to the events receiver file.

To create a SharePoint 2010 event receiver in Visual Studio 2010

1. Start Visual Studio 2010.

2. On the File menu, click New, and then click
   Project.

3. In the New Project dialog box, in the Installed Templates section, expand either
   Visual Basic or Visual C#, expand SharePoint, and then click
   2010.

4. In the template list, click Event Receiver.

5. In the Name box, type VerifyJob.

6. Leave other fields with their default values, and click OK.

7. In the What local site do you want to use for debugging? list, select your site.

8. Select the Deploy as a farm solution option, and then click
   Next.

9. On the Choose Event Receiver Settings page, in the What type of event receiver do you want? list, select
   List Item Events.

10. In the What Item should be the event source? list, select
    Custom List.

11. Under Handle the following events, select the An item is being added and the
    An item is being updated check boxes. Click Finish.

To modify the events receiver file

1. In the events receiver file, add the following code to the class.

   VB

   Copy

   Public Function CheckItem(ByVal properties As SPItemEventProperties) As Boolean
   Dim jobTitle As String = properties.AfterProperties("Title").ToString()
       Dim allowed As Boolean = False
       Dim jobDefWeb As SPWeb = Nothing
       Dim jobDefList As SPList
       Dim privilegedAccount As SPUser = properties.Web.AllUsers("SHAREPOINT\SYSTEM")
      Dim privilegedToken As SPUserToken = privilegedAccount.UserToken
   
       Try
           Using elevatedSite As New SPSite(properties.Web.Url, privilegedToken)
               Using elevatedWeb As SPWeb = elevatedSite.OpenWeb()
                   jobDefWeb = elevatedWeb.Webs("JobDefinitions")
                   jobDefList = jobDefWeb.Lists("Job Definitions")
   
                   For Each item As SPListItem In jobDefList.Items
                       If item("Title").ToString() = jobTitle Then
                           allowed = True
                           Exit For
                       End If
                   Next
   
               End Using
           End Using
   
           Return (allowed)
   
       Finally
           jobDefWeb.Dispose()
       End Try
   End Function
   

   C#

   Copy

   bool checkItem(SPItemEventProperties properties)
     {
         string jobTitle = properties.AfterProperties["Title"].ToString();
         bool allowed = false;
         SPWeb jobDefWeb = null;
         SPList jobDefList;
         SPUser privilegedAccount = properties.Web.AllUsers[@"SHAREPOINT\SYSTEM"];
         SPUserToken privilegedToken = privilegedAccount.UserToken;
         try
         {
             using (SPSite elevatedSite = new SPSite(properties.Web.Url, privilegedToken))
             {
                 using (SPWeb elevatedWeb = elevatedSite.OpenWeb())
                 {
                     jobDefWeb = elevatedWeb.Webs["JobDefinitions"];
                     jobDefList = jobDefWeb.Lists["Job Definitions"];
                     foreach (SPListItem item in jobDefList.Items)
                     {
                         if (item["Title"].ToString() == jobTitle)
                         {
                             allowed = true;
                             break;
                         }
                     }
                 }
             }
             return (allowed);
         }
         finally
         {
             jobDefWeb.Dispose();
         }
     }
   

2. In the EventReceiver1 file, replace the ItemAdding method with the following code.

   VB

   Copy

   Public Overrides Sub ItemAdding(properties as SPItemEventProperties)
       Try
           Dim allowed As Boolean = True
   
           If properties.ListTitle = "Open Positions" Then
               allowed = CheckItem(properties)
           End If
   
           If allowed = False Then
               properties.Status = SPEventReceiverStatus.CancelWithError
               properties.ErrorMessage = _
                 "The job you have entered is not defined in the Job Definitions List"
               properties.Cancel = True
           End If
   
       Catch ex As Exception
           properties.Status = SPEventReceiverStatus.CancelWithError
           properties.ErrorMessage = ex.Message
           properties.Cancel = True
       End Try
   End Sub
   

   C#

   Copy

   public override void ItemAdding(SPItemEventProperties properties)
       {
         try
           {
               bool allowed = true;
   
               if (properties.ListTitle == "Open Positions")
               {
                allowed = checkItem(properties);
               }
   
                  if (!allowed)
               {
                  properties.Status = SPEventReceiverStatus.CancelWithError;
                  properties.ErrorMessage =
                    "The job you have entered is not defined in the Job Definitions List";
                  properties.Cancel = true;
               }
           }
           catch (Exception ex)
           {
               properties.Status = SPEventReceiverStatus.CancelWithError;
               properties.ErrorMessage = ex.Message;
               properties.Cancel = true;
           }
       }
   

3. In the EventReceiver1 file, replace the ItemUpdating method with the following code.

   VB

   Copy

   Public Overrides Sub ItemUpdating(properties as SPItemEventProperties)
           Try
               Dim allowed As Boolean = True
   
               If properties.ListTitle = "Open Positions" Then
                   allowed = CheckItem(properties)
               End If
   
               If allowed = False Then
                   properties.Status = SPEventReceiverStatus.CancelWithError
                   properties.ErrorMessage = _
                     "The job you have entered is not defined in the Job Definitions List"
                   properties.Cancel = True
               End If
   
           Catch ex As Exception
               properties.Status = SPEventReceiverStatus.CancelWithError
               properties.ErrorMessage = ex.Message
               properties.Cancel = True
   
           End Try
   End Sub
   

   C#

   Copy

   public override void ItemUpdating(SPItemEventProperties properties)
       {
   
           bool allowed = true;
   
           if (properties.ListTitle == "Open Positions")
           {
               allowed = checkItem(properties);
           }
   
           try
           {
   
               if (!allowed)
               {
                   properties.Status = SPEventReceiverStatus.CancelWithError;
                   properties.ErrorMessage =
                     "The job you have entered is not defined in the Job Definitions List";
                   properties.Cancel = true;
               }
           }
           catch (Exception ex)
           {
               properties.Status = SPEventReceiverStatus.CancelWithError;
               properties.ErrorMessage = ex.Message;
               properties.Cancel = true;
           }
       }
   

To deploy the project

1. In Solution Explorer, right-click the project, and then click
   Deploy.

2. In the SharePoint site, in the Open Positions list, click
   Add new item.

3. In the Title field, provide a title for a job description that does not exist in the
   Job Definitions list in the secured subsite.

4. Click Save. You receive a message from the event receiver.

5. In the Title field, provide a title for a job description that exists in the
   Job Definitions list in the secured subsite.

6. Click Save. The position is created.

• The solution overrides the ItemAdding and ItemUpdating methods and verifies whether the list that is being added to is the
  Open Positions list. If it is, a call is made to the CheckItem method, passing in the properties that are associated with the event.

• In the CheckItem method, the permissions are elevated to ensure successful access to the secured subsite. The job titles that are in the approved list are compared to the job title of the
  properties.AfterProperties property associated with the event. If any title matches, the
  allowedBoolean variable is set to true, and the method returns.

• Depending on the value of the allowed variable, the calling method either permits the event or sets the
  properties.ErrorMessage property and then cancels the event using
  properties.cancel.