Warning –  this post is somewhat techie so if you’re not a developer you may want to go find something more interesting to do!

I’ve been doing some work with SharePoint Feature Receivers recently and found the official documentation to be somewhat … lacking.

SharePoint Feature Receivers allow you to run code when a Feature such as a web part or template is installed, activated, deactivated and removed. They are often used for installation/setup tasks that can’t be done using XML incantations in Manifest.xml, Elements.xml and Feature.xml.

I am not going to give a step-by-step guide to Feature Receivers (see the excellent How to add a Feature Receiver to a Feature from SharePoint dev wiki) but plan to detail information that I was struggling to find anywhere else.

I am only going to cover the scenario of a Feature encapsulated in a solution package and not installing features directly using STSADM -o InstallFeature as that requires the files are manually placed in the 12\Template\Features\ directory so is not as friendly as distributing .wsp files and is not something that you can really give to customers/server admins.

Scope

SharePoint Features can be targeted at the Farm, Web Application, Site Collection or Web Site scope. The target will effect things like where you can manage the feature activation from in the UI and at which point (and how many times) the Feature receiver events are called.

Scope	Activate/Deactivate Features (2007)
Web Site	Site Actions > Site Settings > Site Administration > Site features
Site Collection	Site Actions > Site Settings > Site Collection Administration > Site collection features
Web Application	SharePoint Central Admin > Application Management > SharePoint Web Application Management > Manage Web application features
Farm	SharePoint Central Admin > Operations > Global Configuration > Manage farm features

SharePoint Feature lifecycle

Stage	Event	Trigger with STSADM -o	Trigger with UI
Add to solution store		AddSolution
Deployment to server/farm	FeatureInstalled	DeploySolution	Central Admin > Operations > Solution Management
Activation to SCOPE	FeatureActivated	ActivateFeature or If Farm scoped then on DeploySolution if ActivateOnDefault is set to true (default) If WebApplication scoped then on creating of a new WebApplication if ActivateOnDefault is set to true. AutoActivateInCentralAdmin is true for Web Application, Site and Web scoped features	See scope table above
Upgrade	FeatureUpgrading (new for 2010)	UpgradeSolution
Deactivation from SCOPE	FeatureDeactivating	On RetractSolution if still activated when called or DeactivateFeature	See scope table above
Retraction from server/farm	FeatureUninstalling	RetractSolution	Central Admin > Operations > Solution Management
Delete from solution store		DeleteSolution

SharePoint Administration Timer Jobs

Deployment and Retraction actually setup a timer job (which can be executed ‘immediately’ or at a specified time. If the “Windows SharePoint Services Administration” Service is not running then you will be warned that these jobs will not be executed and you can force execution by running STSADM -o ExecAdmSvcJobs on all servers in your farm.

Windows Identity

You can’t be sure which windows identity a feature event receiver will be running under as you don’t know if it will be called by STSADM (cmd.exe), “Windows Share Services Administration” timer service (WSSADMIN.EXE) or the WebUI (w3wp.exe with the app pools identity) – so ensure you are not relying on privileges (for example) that may be given to a logged on domain admin when using STSADM but not the app pools identity.

Event	Windows Identity
	Triggered with STSADM	Triggered by UI
FeatureInstalled	Logged on user	Identity of Web Applications Application Pool.
FeatureActivated	Identity of “Windows SharePoint Serviecs Administration” service or Logged on user if forcing by STSADM -o ExecAdmSvcJobs
FeatureDeactivating
FeatureUninstalling	Logged on user	Identity of Web Applications Application Pool.

SharePoint Context

Because you can’t be sure where the FeatureReceiver is being called from (command line, timer service, web ui) you can’t use the normal method of getting a SPSite/SPWeb object.

SPSite site = SPContext.Current.Site;

SPWeb web = SPContext.Current.Web;

Instead you can access the context through SPFeatureReceiverProperties.Feature.Parent see Matt’s handy extension method (beware though, it doesn’t cover Web Application or Farm scopes)

Note – you only get a SPFeatureRecieverProperties.Feature reference with FeatureActivated and FeatureDeactivating – its null for Installed and Uninstalling.

Scope	FeatureActivated and FeatureDeactivating
Web Site	SPWeb
Site CollectionSP	SPSite
Web Application	SPWebApplication
Farm	SPWebService though this seems a little useless – in most cases you would want to get SPFarm.Local

Tags: SharePoint, SharePoint Development