MapTip's GraphicLayer Binding

Question

I can't make MapTip's GraphicLayer binding to work: in xaml:

in my ViewModel, I defined a mapTipLayer member: public FeatureLayer mapTipLayer { get { return (FeatureLayer)GetValue(mapTipLayerProperty); } set { SetValue(mapTipLayerProperty, value); } } public static readonly DependencyProperty mapTipLayerProperty = DependencyProperty.Register("mapTipLayer", typeof(FeatureLayer), typeof(MainPage), new PropertyMetadata(null)); and I am adding layers dynamically and set mapTipLayer: foreach (MapLayer mapLayer in mapLayers) // Loop through List with foreach { Debug.WriteLine(mapLayer.Url); if (mapLayer.Type == "ArcGISTiledMapServiceLayer") { Layers.Add(new ArcGISTiledMapServiceLayer() { ID=mapLayer.ID, Url=mapLayer.Url, Visible=mapLayer.Visible, Opacity=mapLayer.Opacity }); } else if (mapLayer.Type == "FeatureLayer") { FeatureLayer fLayer = new FeatureLayer() { ID = mapLayer.ID, Url = mapLayer.Url, Visible = mapLayer.Visible, Opacity = mapLayer.Opacity }; mapTipLayer = fLayer; Layers.Add(fLayer); } } Can someone help please? Thanks.

SomeGISGuy · Answer

Only FrameworkElements has a DataContext property (which a Layer is not), so you can't do binding without specific a source, either by using the source property in the binding or specifying the element name as Jennifer suggested.

JenniferNery · Answer

If you modify this sample http://help.arcgis.com/en/webapi/silverlight/samples/start.htm#MapTipWidget to set MapTip GraphicsLayer property in XAML with Element Binding:GraphicsLayer="{Binding ElementName=MyMap, Path=Layers[MyGraphicsLayer]}"

and comment-out this line in code-behind under (QueryTask_ExecuteCompleted)
//MyMapTip.GraphicsLayer = graphicsLayer;
the sample still works.

In your sample, it is difficult to tell what is wrong with your binding. But I suggest you check that MapTip.DataContext is pointed to an instance of your Model.

For example this binding statement:
GraphicsLayer="{Binding SomeProperty}" 
assumes that DataContext has been set to an object that contains a property SomeProperty of type GraphicsLayer. FeatureLayer is GraphicsLayer so it should have worked with your mapTipLayer property.

I suspect that DataContext is null or not the object that contains this property. Do you define a model class or are you using MainPage as your model? DependencyProperty.Register("mapTipLayer", typeof(FeatureLayer), typeof(  MainPage), new PropertyMetadata(null));

I think that if you are following MVVM pattern, mapTipLayer should have been a property of your Model class, separate from the MainPage UserControl.

SteveLi · Answer

in my xaml, i also tried

GraphicsLayer="{Binding mapTipLayer}"

it didn't work either.