In the SqlArticlesProvider, I added a new Public method to retrieve something from the database. In Visual Studio, the new method is not shown by Intellisense using the SiteProvider approach -- SiteProvider.Articles. If I use "new SqlArticlesProvider()." the new class appears in the Intellisense list.

What am I missing? Must all methods in SqlArticlesProvider be public overrides of an abstracted class defined in ArticlesProvider?

Thanks in advance for any help.
Tom

Hi,
SiteProvider.Articles points to an abstract ArticlesProvider's static function which creates an instance of needed provider class, in this case SqlArticlesProvider. (SqlArticlesProvider implements ArticlesProvider) and returns it as ArticlesProvider.

So, SiteProvider.Articles "sees" only function known to him.

What you can do: define your new function as "public abstract" in ArticlesProvider and implement it SqlArticlesProvider.

Or as you just did, create a new instance of SqlArticlesProvider class and use it as object.

Essentially, yes. The Liskov Substitution Principle again.

This is because the application is written to be able to work against any provider that implements ArticlesProvider.

The actual concrete provider implementation is determined by using reflection at runtime. The actual inside nuts and bolts of any particular concrete provider does not matter to the methods that call it. Because they all implement ArticlesProvider, the caller knows that the abstract methods and properties of ArticlesProvider are guaranteed to be available.

SiteProvider.Articles is of type ArticlesProvider, so if you program against SiteProvider.Articles, it can only "see" the members defined in ArticlesProvider.

If any new methods are "exclusive" to a class, and not first defined as abstract in ArticlesProvider, then there is no way that Intellisense can know about them.

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