Question

When using Unity 2.0 for dependency injection within a web application, it appears that user controls, pages, etc will all need make explicit calls to retrieve the container and “fetch” the dependencies … so using the annotations like [dependency] won’t offer any value. This is likely since the location of the container (application context, http context cache, etc.) is unknown in the web configuration.

Since Unity itself provides method interception, isn’t there a way to “tell” unity how to fetch the container correctly when you build your own web application? Rather than having to create base classes for page, etc.?

Answer 1

The problem is that the WebForms Pages and Controls are not set up to allow for construction by dependency injection, so Unity never gets invoked at all unless the class invokes Unity itself. I’ve found the best pattern in these cases is to invoke the DI framework in the constructor via a Service Locator and then use annotations to mark dependency properties. Something like this:

public MyPage()
{
    // Injector is a wrapper class so you can change the underlying DI framework
    // later if necessary.
    Injector.Inject(this); 
}

[Dependency]
public SomeService MyService {get;set;}