c#xaml mvvm xamarin.forms arcgis-runtime-net

Expose XAML Element to ViewModel to run methods Xamarin Forms

I need to be able to run methods on a XAML element in my ViewModel, I have 3 files - DataPrepPage.cs, DataPrepPage.xaml and DataPrepViewModel.cs.

In my XAML(DataPrepPage.xaml) page I have the element like this:

<esriUI:MapView x:Name="MapElement" 
                Map="{Binding Map}"/>

I set my binding context on the parent grid element like this:

<Grid.BindingContext>
     <local:DataPrepViewModel/>
</Grid.BindingContext>

Of course I can access my MapView element and methods in the code-behind like this for example:

MapElement.GraphicsOverlays.Add(MyOverlay);

So the problem is I need to be able to do this in the ViewModel but the x:Name does not expose it to my ViewModel.

At the moment I have a static in my ViewModel

public static MapView MapView;

And I assign my element to it in the constructor of my page code-behind:

    public DataPrepPage ()
    {
        InitializeComponent ();
        DataPrepViewModel.MapView = MapElement;
    }

Which allows me to do this in my ViewModel:

MapView.GraphicsOverlays.Add(MyOverlay);

So the question is:

How do I expose the element to my ViewModel without using a static? || How can I run methods on an element from the ViewModel?

Solution

The whole idea behind MVVM is that your view and viewmodel are de-coupled. You're asking how to couple them together again. Short answer: don't.

You can Bind the GraphicsOverlays in XAML:

        <esri:MapView x:Name="MapView1" Height="517" MapViewTapped="MapView1_MapViewTapped">

            <!-- Add a Map. -->
            <esri:Map x:Name="Map1">

                <!-- Add a backdrop ArcGISTiledMapServiceLayer. -->
                <esri:ArcGISTiledMapServiceLayer ID="myArcGISTiledMapServiceLayer" 
                  ServiceUri="http://services.arcgisonline.com/ArcGIS/rest/services/Canvas/World_Light_Gray_Base/MapServer" />

            </esri:Map>

            <!-- Add a MapView.GraphicsOverlays collection. -->
        <esri:MapView.GraphicsOverlays>

            <!-- Add a GraphicsOverlay to hold Graphics added via code behind from a FindTask operation. Set the Renderer to draw the polygon graphics. -->
            <esri:GraphicsOverlay Renderer="{StaticResource mySimpleRenderer}"/>

        </esri:MapView.GraphicsOverlays>

    </esri:MapView>