How to share an implementation of the interface using prism?

Question

Based on MSDN,if you registered an existing instance of an object using the RegisterInstance method, the container returns the same instance for all calls to Resolve or ResolveAll or when the dependency mechanism injects instances into other classes.

I create a project for dataService layer and used

container.RegisterInstance<IQuoteSource>(new IBQuoteSource());

I expect whenever I need IQuoteSource, only one instance is created during the lifetime of the application. But in another project assembly when I use the interface in the constructor, what happend is another IBQuoteSource is created.(As I can see the constructor of IBQuoteSource is called again) So how to share one implementation of the interface across the application?

public ClickViewModel( IQuoteSource quoteSource)
{
    this.quoteSource = quoteSource;
    ComboItems = new List<string>() { "GTC Order", "Day Order" };
    SelectedComBoItem = ComboItems[1];
}

Answer 1

I think you've misinterpeted the doco - using RegisterInstance means that the same implementation of the registered interface will be returned, not the same concrete instance.

To get what you want, you need to use a ContainerControlledLifetimeManager:

container.RegisterInstance<IQuoteSource>( new IBQuoteSource()
                                        , new ContainerControlledLifetimeManager()
                                        ); 

(note: untested line of code!) This will effectively use the singleton pattern with your container - the initial instance created is used every time that interface is resolved.

Also, just to nitpick - I would suggest you change the name of IBQuoteSource - it's an actual class, not an interface so ideally it shouldn't have a capital I prepended on the front of the class name.