MvvmCross migration causing a Xamarin Custom iOS View Presenter issue - xamarin

Question

While creating a CustomIosViewPresenter (of type MvxIosViewPresenter), in MVVMCross 5.x, there was a Show override that I was able to use to get the IMvxIosView so as to update the UIViewController presentation style using the PresentationValues from the ViewModel.
I had this code and it worked:
// Worked before
public override void Show(IMvxIosView view, MvvmCross.ViewModels.MvxViewModelRequest request)
{
if (request.PresentationValues != null)
{
if (request.PresentationValues.ContainsKey("NavigationMode") &&
request.PresentationValues["NavigationMode"] == "WrapInModalWithNavController")
{
var vc = view as IModalPresentation;
vc.ModalPresentationAttribute = new MvxModalPresentationAttribute
{
WrapInNavigationController = true,
ModalPresentationStyle = UIModalPresentationStyle.OverFullScreen,
ModalTransitionStyle = UIModalTransitionStyle.CoverVertical
};
}
}
base.Show(view, request);
}
But after migrating to MvvmCross 7.1, the older override doesn't work anymore and I have to use this instead, but there is no view passed into the Show override, how do I get it?
I tried this code below, but view is null and it's not able to cast it this way var view = viewType as IMvxIosView;
// Doesn't work now
public override Task<bool> Show(MvxViewModelRequest request)
{
if (request.PresentationValues != null)
{
if (request.PresentationValues.ContainsKey("NavigationMode") &&
request.PresentationValues["NavigationMode"] == "WrapInModalWithNavController")
{
var viewsContainer = Mvx.IoCProvider.Resolve<IMvxViewsContainer>();
var viewType = viewsContainer.GetViewType(request.ViewModelType);
var view = viewType as IMvxIosView;
var vc = view as IModalPresentation;
vc.ModalPresentationAttribute = new MvxModalPresentationAttribute
{
WrapInNavigationController = true,
ModalPresentationStyle = UIModalPresentationStyle.OverFullScreen,
ModalTransitionStyle = UIModalTransitionStyle.CoverVertical
};
}
}
return base.Show(request);
}
The reason I need this is because without this function when I close the special flow of view controllers that need this, its not closing all the view controllers in that flow, it closes only one of them at a time.

Answer 1

What you would normally do with MvvmCross if you want to navigate within a Modal ViewController is firstly add a MvxModalPresentationAttribute to the modal that will host the rest of the navigation where you set WrapInNavigationController to true.
For the children, it would just be regular child navigation, no attributes needed.
If you then want to control how the modal is popping you would create your own MvxPresentationHint and register it in your presenter using AddPresentationHintHandler.
Then you would in your ViewModel where you want to change the presentation call NavigationService.ChangePresentation(your hint).
As for the Presentation Hint, it should probably just call CloseModalViewControllers and that would probably do what you want.

Answer 2

TLDR: Feel for the developers that will come after you and build stuff the right way
So I dug into the MvvmCross MvxIosViewPresenter source code and was able to use this new override CreateOverridePresentationAttributeViewInstance()
I needed the request object to see the presentation values so I updated the Show function that gets called before the other override as follows:
MvxViewModelRequest _request;
public override Task<bool> Show(MvxViewModelRequest request)
{
_request = request;
return base.Show(request);
}
And I was able to get the ViewController this way, in order to selectively present it as a modal:
{
var view = base.CreateOverridePresentationAttributeViewInstance(viewType);
if (_request.PresentationValues.ContainsKey("NavigationMode") &&
_request.PresentationValues["NavigationMode"] == "WrapInModalWithNavController")
{
var vc = view as IModalPresentation;
vc.ModalPresentationAttribute = new MvxModalPresentationAttribute
{
WrapInNavigationController = true,
ModalPresentationStyle = UIModalPresentationStyle.OverFullScreen,
ModalTransitionStyle = UIModalTransitionStyle.CoverVertical
};
return vc;
}
return view;
}
And then the closing of the modal was another challenge, that I was able to figure out using the TryCloseViewControllerInsideStack and ChangePresentation overrides