Caliburn.Micro 3.0 equivalent to Xamarin.Forms Navigation.PushModalAsync - xamarin

Question

Does Caliburn.Micro 3.0 (and Caliburn.Micro.Xamarin.Forms) implement functionality to mimic/support Navigation.PushModalAsync in Xamarin.Forms?

Answer 1

No. It's not build in, but its easy to enhance it. Usually, MvvM frameworks are navigating by ViewModels. Caliburn is following this pattern. So it needs some kind of navigation service. This navigationservice is responsible for creating the Views for the ViewModels and call the view framework (Xamarin.Froms in our case) specific navigation functions. NavigationPageAdapter is the thing we are searching for. Now let's enhance it.
public interface IModalNavigationService : INavigationService
{
Task NavigateModalToViewModelAsync<TViewModel>(object parameter = null, bool animated = true);
// TODO: add more functions for closing
}
public class ModalNavigationPageAdapter : NavigationPageAdapter, IModalNavigationService
{
private readonly NavigationPage _navigationPage;
public ModalNavigationPageAdapter(NavigationPage navigationPage) : base(navigationPage)
{
_navigationPage = navigationPage;
}
public async Task NavigateModalToViewModelAsync<TViewModel>(object parameter = null, bool animated = true)
{
var view = ViewLocator.LocateForModelType(typeof(TViewModel), null, null);
await PushModalAsync(view, parameter, animated);
}
private Task PushModalAsync(Element view, object parameter, bool animated)
{
var page = view as Page;
if (page == null)
throw new NotSupportedException(String.Format("{0} does not inherit from {1}.", view.GetType(), typeof(Page)));
var viewModel = ViewModelLocator.LocateForView(view);
if (viewModel != null)
{
TryInjectParameters(viewModel, parameter);
ViewModelBinder.Bind(viewModel, view, null);
}
page.Appearing += (s, e) => ActivateView(page);
page.Disappearing += (s, e) => DeactivateView(page);
return _navigationPage.Navigation.PushModalAsync(page, animated);
}
private static void DeactivateView(BindableObject view)
{
if (view == null)
return;
var deactivate = view.BindingContext as IDeactivate;
if (deactivate != null)
{
deactivate.Deactivate(false);
}
}
private static void ActivateView(BindableObject view)
{
if (view == null)
return;
var activator = view.BindingContext as IActivate;
if (activator != null)
{
activator.Activate();
}
}
}
We just declared the interface IModalNavigationService that extends INavigationService and implement it in our ModalNavigationPageAdapter. Unfortunately Caliburn made alot of functions private, so we have to copy them over to our inherited version.
In caliburn you can navigate via navigationservice.For<VM>().Navigate(). We want to follow this style, so we have to implement something like navigationservice.ModalFor<VM>().Navigate() which we do in an extension method.
public static class ModalNavigationExtensions
{
public static ModalNavigateHelper<TViewModel> ModalFor<TViewModel>(this IModalNavigationService navigationService)
{
return new ModalNavigateHelper<TViewModel>().AttachTo(navigationService);
}
}
This method returns a ModalNavigateHelperthat simplifies the usage of our navigation service (similar to Caliburn's NavigateHelper). It's nearly a copy, but for the IModalNavigationService.
public class ModalNavigateHelper<TViewModel>
{
readonly Dictionary<string, object> parameters = new Dictionary<string, object>();
IModalNavigationService navigationService;
public ModalNavigateHelper<TViewModel> WithParam<TValue>(Expression<Func<TViewModel, TValue>> property, TValue value)
{
if (value is ValueType || !ReferenceEquals(null, value))
{
parameters[property.GetMemberInfo().Name] = value;
}
return this;
}
public ModalNavigateHelper<TViewModel> AttachTo(IModalNavigationService navigationService)
{
this.navigationService = navigationService;
return this;
}
public void Navigate(bool animated = true)
{
if (navigationService == null)
{
throw new InvalidOperationException("Cannot navigate without attaching an INavigationService. Call AttachTo first.");
}
navigationService.NavigateModalToViewModelAsync<TViewModel>(parameters, animated);
}
}
Last but not least, we have to use our shiny new navigation service instead of the old one. The App class is registering the NavigationPageAdapter for the INavigationService as singleton in PrepareViewFirst. We have to change it as follows
public class App : FormsApplication
{
private readonly SimpleContainer container;
public App(SimpleContainer container)
{
this.container = container;
container
.PerRequest<LoginViewModel>()
.PerRequest<FeaturesViewModel>();
Initialize();
DisplayRootView<LoginView>();
}
protected override void PrepareViewFirst(NavigationPage navigationPage)
{
var navigationService = new ModalNavigationPageAdapter(navigationPage);
container.Instance<INavigationService>(navigationService);
container.Instance<IModalNavigationService>(navigationService);
}
}
We are registering our navigation service for INavigationService and IModalNavigationService.
As you can see in the comment, you have to implement close functions that call PopModalAsync by yourself.