topic Re: MapView Events handled in ViewModel in .NET Maps SDK Questions

MapView Events handled in ViewModel

HS_PolkGIS — Thu, 02 Nov 2023 11:46:56 GMT

Does ESRI have a single example of a MapView event being handled from a ViewModel using the best MVVM approach possible?

I am using the basic Display a Map example from ESRI and added Prism for commands and the event aggregator. How would you handle the GeoViewTapped event in the MapViewModel?

Edit

Thank you for the responses already. I should have included this in the original post.

Using WPF and .NET 6 and starting with this tutorial. https://developers.arcgis.com/net/maps-2d/tutorials/display-a-map/

Re: MapView Events handled in ViewModel

BjørnarSundsbø1 — Wed, 01 Nov 2023 21:27:36 GMT

Hi,

This post covered some of this, but unfortunately it appears the links are broken. https://community.esri.com/t5/arcgis-maps-sdks-native-blog/blogpost-navigating-the-mapview-from-a-viewmodel/ba-p/886181

I don't have the opportunity to search or access my version of this code, but look for MapViewController in some of Morten's git repositories. While not a full answer, at least it is something to point you in the right direction.

I would implement the GeoViewTapped through custom WeakEventManager implementations to avoid memory leaks.

Re: MapView Events handled in ViewModel

dotMorten_esri — Wed, 01 Nov 2023 21:44:21 GMT

The approach is the same you use with any view events - the Maps SDK isn't special in this regard. Depending on which UI framework you use, it's slightly different though. For instance MAUI using the MAUI Community Toolkit you can execute a command from an event:

<esri:MapView Map="{Binding Map, Source={StaticResource VM}}"> <esri:MapView.Behaviors> <mauitoolkit:EventToCommandBehavior EventName="GeoViewTapped" x:TypeArguments="esri:GeoViewInputEventArgs" Command="{Binding GeoViewTappedCommand, Source={StaticResource VM}}" /> </esri:MapView.Behaviors> </esri:MapView>

In WPF you can use the Behaviors SDK to do the same thing:

<esri:MapView Map="{Binding Map, Source={StaticResource VM}}"> <Behaviors:Interaction.Triggers> <Behaviors:EventTrigger EventName="GeoViewTapped" > <Behaviors:InvokeCommandAction Command="{Binding GeoViewTappedCommand, Source={StaticResource VM}}" PassEventArgsToCommand="True" /> </Behaviors:EventTrigger> </Behaviors:Interaction.Triggers> </esri:MapView>

In WinUI and UWP, you can bind straight to a method in your VM using x:Bind:

GeoViewTapped="{x:Bind VM.OnGeoViewTapped}"

Prism also offers some documentation on this:
- https://prismlibrary.com/docs/wpf/interactivity/event-to-command.html
- https://prismlibrary.com/docs/maui/behaviors/eventtocommandbehavior.html

Re: MapView Events handled in ViewModel

dotMorten_esri — Wed, 01 Nov 2023 22:00:57 GMT

You don't really need a controller for reacting to events (see my other response). For performing operations on the view, this PR in the works might be of interest: https://github.com/Esri/arcgis-maps-sdk-dotnet-toolkit/pull/528 (you could just pull the controller code and have a play with it until this is in the toolkit)

Re: MapView Events handled in ViewModel

JoeHershman — Thu, 02 Nov 2023 12:51:14 GMT

You don't actually say what you are developing in. If you have Prism setup, I would use the CommandToEvent from Prism instead of the MAUI toolkit like Morten shows below. But basically same principle. As a rule if using Prism stick with all of their implementations, don't mix and match MAUI toolkit and Prism implementations

Or you could just fire your own events, which is what I have done. You can inject IEventAggregator into the code behind that has the MapView . I create an Event for each of the MapView interactions and wire them up

private void WireUpMapViewEventHandlers(IEventAggregator eventAggregator) { MapView.GeoViewTapped += (s, e) => { eventAggregator.GetEvent<GeoViewTappedEvent>().Publish(e); }; MapView.GeoViewDoubleTapped += (s, e) => { eventAggregator.GetEvent<GeoViewDoubleTappedEvent>().Publish(e); }; MapView.GeoViewHolding += (s, e) => { eventAggregator.GetEvent<GeoViewHoldingEvent>().Publish(e); }; MapView.ViewpointChanged += (s, e) => { eventAggregator.GetEvent<ViewpointChangedEvent>().Publish(MapView.VisibleArea.Extent); }; MapView.NavigationCompleted += (s, e) => { eventAggregator.GetEvent<NavigationCompletedEvent>().Publish(MapView.VisibleArea.Extent); }; }

This way everything if just published and I can hook into in any Module

Re: MapView Events handled in ViewModel

HS_PolkGIS — Thu, 02 Nov 2023 12:38:10 GMT

Joe, thank you for the response on this and your snippet is exactly what I am looking for. However, I am a bit confused on how to achieve this.

How are you injecting the IEventAggregator into the View?

For ViewModels, I would pass the IEventAggregator as a parameter in the constructor.

Re: MapView Events handled in ViewModel

JoeHershman — Thu, 02 Nov 2023 13:11:43 GMT

You still haven't mentioned what framework you are using.

You should be able to inject the IEventAggregator into the View code behind. Prism will handle this. I have WPF and Xamarin Forms code that use this approach for events associated to View updates or actions

public MobileAppMapView(IEventAggregator eventAggregator) { _eventAggregator = eventAggregator; InitializeComponent(); WireUpMapViewEventHandlers(eventAggregator); SetupEventListeners(eventAggregator); }

I have not done this with a View using regions in Xamarin, because when I originally built out my Xamarin architecture Prism hadn't introduced Regions in Xamarin yet. But it should still work

Re: MapView Events handled in ViewModel

HS_PolkGIS — Thu, 02 Nov 2023 14:23:36 GMT

My framework is WPF and I have tried what you suggested but I run into an error when adding a parameter to the View Constructor.

This is where I register (autofac) the View in the Application_Startup, the XAML where the view is used, and the View's code behind. The XAML shows a warning and throws a runtime error due to lacking a parameter-less constructor.

builder.RegisterType<MapView>().AsSelf();

<mViews:MapView DataContext="{Binding MapViewModel}" />

private IEventAggregator _eventAggregator; public MapView(IEventAggregator eventAggregator) { InitializeComponent(); _eventAggregator = eventAggregator; RegisterMapViewEvents(_eventAggregator); } private void RegisterMapViewEvents(IEventAggregator eventAggregator) { MyMapView.GeoViewTapped += (s, e) => { eventAggregator.GetEvent<OnClickMapEvent>().Publish(e); }; }

Re: MapView Events handled in ViewModel

JoeHershman — Thu, 02 Nov 2023 16:17:04 GMT

So if you are using Prism, then you should be using the Prism container. I think Prism 7 had an Autofac version, but they depreciated that. starting at Prism 8. I would suggest Prism.DryIoc as that is the direction they are moving with Prism 9. You want to add one of the Prism packages with a container either Prism.Unity or Prism.DryIoc and then let Prism do the rest

Prism provides a method in App.Xaml.cs to override with registrations.

protected override void RegisterTypes(IContainerRegistry containerRegistry) { containerRegistry.Register<IComboBoxItem, ComboBoxItem>(); containerRegistry.Register<IToolbarCommand, ToolbarCommand>(); containerRegistry.RegisterSingleton<IConnectionCheck, PortalConnectionCheck>(); containerRegistry.RegisterSingleton<ILog4NetFacade, Log4NetLogger>(); //If you did not have Modules or Regions you could register a view for Navigation here containerRegistry.RegisterForNavigation<MobileAppMapView, MobileAppMapViewModel>(); }

If you have Modules the initialization is done in the IModule implementation and would be along these lines

/// <summary> /// Map Module is primary application module responsible for inital loading /// of the map and all interations with the MapView /// </summary> public class MapModule : ModuleBase // I have a ModuleBase class that implements IModule so that common initialization code is put there { public override void RegisterTypes(IContainerRegistry containerRegistry) { base.RegisterTypes(containerRegistry); containerRegistry.Register<IMapLoadService, MapLoadService>(); } public override void OnInitialized(IContainerProvider containerProvider) { base.OnInitialized(containerProvider); //RegionManager comes from base class this is is how one gets RegionManager in Module // RegionManager = containerProvider.Resolve<IRegionManager>(); RegionManager.RegisterViewWithRegion(RegionNames.MapRegion, typeof(MobileAppMapView)); } }

There is no need to be setting a DataContext, Prism does that for you

As an aside: I would avoid naming my View MapView, I find this confuses things sometimes because it is the same name as the esri class

Re: MapView Events handled in ViewModel

JoeHershman — Thu, 02 Nov 2023 23:29:02 GMT

Attached is a sample of Prism setup using the sample app shown in help. Even with the APIKey I am getting a token error, but the general setup of Prism with injecting IEventAggregator all works

Re: MapView Events handled in ViewModel

HS_PolkGIS — Fri, 03 Nov 2023 14:59:34 GMT

I will take a look at your sample and thanks again for your help. Your above post will be marked as the answer as I think that does answer the MapView question.