xamarin,viewmodel,mvvmcross,lookup-tables , Why “removing any who's ViewModel PropertyType is an interface” when creating the MvvMCross View lookup table


Why “removing any who's ViewModel PropertyType is an interface” when creating the MvvMCross View lookup table

Question:

Tag: xamarin,viewmodel,mvvmcross,lookup-tables

When creating the default View lookup table in MvvMCross, there is a step "removing any who's ViewModel PropertyType is an interface". (http://slodge.blogspot.de/2013/01/overriding-view-lookup-convention-used.html) Why is this step performed?

It's clear, that you can't instantiate an interface, but I can navigate to Interface implementing ViewModels with ShowViewModel<IMyViewModel>(), if I write Mvx.Register<IMyViewModel, MyViewModel>(). Isn't the View creator using the DI table?


Answer:

When we were looking at this area of Mvx back in 2013 we didn't really find any users who wanted to hide each ViewModel behind interfaces, and we really didn't come across users who wanted to navigate using interfaces.

Instead users generally wanted:

In the case where interfaces were used for groupings - e.g. for IRefreshableViewModel then it was quite common to see a base View class implemented too - and to see it have an IRefreshableViewModel ViewModel property. It is these views that are supposed to be removed in the step you mention.

Because of this, we didn't use interfaces for the default ViewModel navigation... and so ViewModel's aren't in the DI/IoC/ServiceLocator lookup system.

However, we did leave Mvx open for adjustment - it's in the manifesto - so if your app wants to navigate by interfaces and if you want your Views to reference ViewModel interfaces instead of concrete classes, then you can absolutely do this - you'll just need to override the Setup steps to put your View-ViewModel lookup and your ViewModel factory in place (there are actually details on this in the wiki)


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