PRISM WPF - Navigation creates new view every time

The problem was in such a place that I never expected... Debugging the Navigation API lead me to the RegionNavigationContentLoader

public object LoadContent(IRegion region, NavigationContext navigationContext)

When i stepped further down the code, I noticed a call to:

protected virtual IEnumerable<object> GetCandidatesFromRegion(    IRegion region,    string candidateNavigationContract)

I noticed that the naming here is key to matching the view to the view-model.

In my example, the name for each part was:

public class SiteDetailsViewModel { ... } // ViewModelpublic class SiteDetailsView { ... } // ViewViewNames.SiteView = "SiteView" // ViewName constant

When I inadvertently made the following change:

ViewName.SiteView = "SiteDetailsView"

Everthing worked.

Conclusion

The name of the ViewModel must start with the same name you used to identify your view.

I tested this out by changing my view to:

public class MyView { ... }

and still using the same view name to register with the container and navigation:

_container.RegisterType<object, MyView>(ViewNames.SiteView);..._regionManager.RequestNavigate(RegionNames.DetailRegion,    ViewNames.SiteView + "?ID=" + site.ID);

This seems to work also. So it seems the name of the View-Model is intrinsically linked to the view name used to navigate to that view.

NOTE

This is only when you're using IoC and Unity with the PRISM 4 Navigation API. This doesn't seem to happen when using MEF.

Further Investigation

I am also aware that some guides have told us to use the typeof(MyView).FullName when registering the view with the Container...

_container.RegisterType<object, MyView>(typeof(MyView).FullName);

I personally think this is a mistake. By using the view's full name, you are creating a depending between the view and any one who wishes to navigate to that view...

_regionManager.RequestNavigate(RegionNames.DetailRegion,    typeof(MyView).FullName + "?ID=" + site.ID);

The registration of the View and the ViewModel is the problem. To have only one view you have to use a different lifetime manager. Without specifying a lifetime manager the TransientLifetimeManager is used which always returns a new instance on resolve. To have only one single instance you have to use the ContainerControlledLifetimeManager or the HierarchicalLifetimeManager:

_container.RegisterType<SiteDetailsViewModel>(new ContainerControlledLifetimeManager());_container.RegisterType<object, SiteDetailsView>(ViewNames.SiteView, new ContainerControlledLifetimeManager());