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I'm using PRISM 4 Navigation API with Unity in WPF. I have a tree-view that initiates a RequestNavigate passing in the selected tree node's ID (GUID).

_regionManager.RequestNavigate(RegionNames.DetailRegion,
    ViewNames.SiteView + "?ID=" + site.ID);

In my module, I have registered the view/view-model like so:

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

When I select different nodes from the tree view, the DetailsRegion displays the SiteDetailsView as expected, but when I like to navigate back to the same node, a new view/view-model is created.

I tried to break at IsNavigationTarget(NavigationContext navigationContext) but this method appears to never be called.

Where have i gone wrong? Thanks in advance.

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1 Answer

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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());
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