SharePoint Dependency Injection Approach
I just finished delivering a SharePoint workflow application in which I developed what could be called a start to framework that I would like to reuse in my next project. The framework currently has many features such as:
- An “Object-List Mapping” infrastructure complete with lazy initialization of objects and collections, converters, and caching
- A list item event broker
- Several handy web controls
- Logging
- State management
- Plenty of Utility Helpers
Each major feature is defined with an interface, and there is a single context class scoped to an SPWeb that holds references to each feature provider. For this last application, and I imagine I will do this for most applications going forward, I extended the context class to hold additional references to application-specific business logic helpers and data access interfaces.
In order to accomplish dependency injection of the feature providers, there is a context factory interface that is responsible for constructing and initializing contexts. I implemented a static ”default” context factory that when called upon, it first looks in the SPWeb property bag to see if a predefined custom context factory type has been specified. If it finds one, it constructs a new instance of the custom factory and returns the context from the custom factory’s CreateContext method.
public static class SPAppContextFactory { public const string CustomSPAppContextFactoryKey = "custom_context_factory_key"; public static void RegisterSPAppContextFactory<T>(this SPWeb web) where T : ISPAppContextFactory { web.AllProperties[CustomSPAppContextFactoryKey] = typeof(T).AssemblyQualifiedName; web.Update(); } public static void UnregisterSPAppContextFactory(this SPWeb web) { if (web.Properties.ContainsKey(CustomSPAppContextFactoryKey)) { web.AllProperties[CustomSPAppContextFactoryKey] = null; web.Update(); } } public static SPAppContext CreateSPAppContext(this SPWeb web) { // First check Web Properties if an alternate factory is specified if (web.AllProperties.ContainsKey(CustomSPAppContextFactoryKey)) { string customFactoryTypeName = web.AllProperties[CustomSPAppContextFactoryKey]; Type customFactoryType = Type.GetType(customFactoryTypeName, true); ISPAppContextFactory customFactory = (ISPAppContextFactory)Activator.CreateInstance(customFactoryType); return customFactory.CreateContext(web); } // Create the Default Context return new SPAppContext(web); } |
You can now register your applications custom context factory in the FeatureActivated method of a feature receiver. You’ll need to include the namespace of your static factory class in order to make the extension methods available, and then simply call the RegisterSPAppContextFactory extension method .
public override void FeatureActivated(SPFeatureReceiverProperties properties) { var web = (SPWeb)properties.Feature.Parent; web.RegisterSPAppContextFactory<MyCustomContextFactoryClass>(); } public override void FeatureDeactivating(SPFeatureReceiverProperties properties) { var web = (SPWeb)properties.Feature.Parent; web.UnregisterSPAppContextFactory(); } |
The context factory now serves as a single place where all dependencies are wired up, and the framework is now able to instantiate custom contexts without being aware of any feature provider implementation.
November 10th, 2012 at 3:51 am
Hello, Trent.
As I understand you suggest to store some instance of the known type in Web properties and later any time its needed get an instance from Web properties again, typecast and use.
Thank you for your suggestion!