GpsLayer and MVVM issues

EladNachmias

Hello,

I am trying to use the GpsLayer under MVVM architecture, however, as it seems - no luck yet.

Binding the GeoPositionWatcher to a property when using MVVM does not work (getter not reached).
The reason is that GpsLayer inherits DependencyObject, but DependencyObject does not implement DataContext.
So actually it is impossible to bind the DependencyProperty to a property on the ViewModel.
Microsoft states that the DO should inherit the DataContext from the containing FrameworkElement (esri:map in this case), but that in fact doesn't happen.

Would love for some opinion from ESRI about this - have you tested this in MVVM architecture?

Also - when a certain object/class implements visual capabilities (GpsLayer has  a GraphicsLayer, that allows actual creation of geometries, shapes, lines, etc), it should inherit FrameworkElement - providing the infrastructure of inheritance through dependency properties that the WPF Dependency Object+Dependency Property Backing data store offers.

Not to mention - The actual inheritance through DependencyObject  and not through FrameworkElement might cause visual problems (And I have personally had situations where the layer stopped refreshing and stopped redrawing, I would suggest this is related to the WPF rendering engine).

AnttiKajanus1

When working with Caliburn.Micro you can use DataContextProxy to define DataContext from the Map so you can bind to it since Caliburn handles ViewModel mapping automatically.

DataContext can be proxied with solution like this:

  public class DataContextProxy : Freezable     {         #region Overrides of Freezable          protected override Freezable CreateInstanceCore()         {             return new DataContextProxy();         }          #endregion          public object Data         {             get { return (object)GetValue(DataProperty); }             set { SetValue(DataProperty, value); }         }          public static readonly DependencyProperty DataProperty =             DependencyProperty.Register("Data", typeof(object), typeof(DataContextProxy), new UIPropertyMetadata(null));     }

And in the XAML you can use it like this

        <esri:Map>             <esri:Map.Resources>                     <local:DataContextProxy x:Key="proxy" Data="{Binding}" />             </esri:Map.Resources>             <esri:ArcGISTiledMapServiceLayer ID="PhysicalTiledLayer"                        Url="http://services.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer"/>              <esri:GraphicsLayer ID="MyGraphicsLayer"                      GraphicsSource="{Binding Path=Data.SearchResults, Source={StaticResource proxy}}" Renderer="{StaticResource MySimpleRenderer}" />         </esri:Map>

This is just one solution but seems to work quite well in the cases where you don't set ViewModels explicitly in the XAML.

Edit:
Note that when using proxy like this, you need to prefix binding to real proxy property since the solution is kind of relative binding. In this case, path is set to Data.SearchResults.