Bind graphics of GraphicLayer.[Bind GraphicCollection]

[StefhanCampos]

hi,

I am using MVVM approuch and i need bind graphics of GraphicLayer i try:

<esri:GraphicsLayer ID="test" Graphics="{Binding graphics}" />


private GraphicCollection graphics;
        public GraphicCollection Graphics
        {
            get {
                return graphics;
            }
            set {
                graphics = value;
                OnPropertyChanged("graphics");
            }
        }


the application hangs, not display nothing...anyone know how i can solve this issue?

[JenniferNery]

You can define your GraphicCollection in Xaml under UserControl.Resources as such:

 
  <esri:GraphicCollection x:Key="MyGraphics" />

and then create the binding to Graphics this way:

  <esri:GraphicsLayer ID="MyGraphicsLayer"
                                Graphics="{Binding Source={StaticResource MyGraphics}}">

Any changes to your GraphicCollection should affect the Graphics in your GraphicsLayer.

Jennifer

[BjørnarSundsbø]

Hi

How do I get MyGraphics to contain the data from my ViewModels Graphics collection without monitoring changes to my viewmodel and adding them to the resource?

[JenniferNery]

If you want to define the Binding in XAML, I don't see another way to do so without defining an instance of your ViewModel under Resource.

If your ViewModel object looked like this

   public class MyViewModelObject : INotifyPropertyChanged
    {
        public MyViewModelObject()
        {
            Graphics = new GraphicCollection();
        }
        private GraphicCollection graphics;
        public GraphicCollection Graphics
        {
            get { return graphics; }
            set
            {
                if (graphics != value)
                {
                    graphics = value;
                    OnPropertyChanged("Graphics");
                }
            }            
        }
        public event PropertyChangedEventHandler PropertyChanged;
        public void OnPropertyChanged(string property)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(property));
        }

You might be expecting that when you set your UserControl's DataContext to an instance of your ViewModel in code-behind like this:

            MyViewModelObject obj = new MyViewModelObject();
            this.DataContext = obj;

the following XAML-code would just work:

            <esri:GraphicsLayer ID="MyGraphicsLayer" Graphics="{Binding Graphics}">

Unfortunately, this is not the case. While your Map can inherit the DataContext of your UserControl, GraphicsLayer will not. GraphicsLayer, unlike Map or any other UIElement, does not have a DataContext and will therefore fail to resolve this type of Binding.

If you wish to define the Binding in code-behind, these two are equivalent:
XAML:

        <Grid.Resources>
            <local:MyViewModelObject x:Key="obj"/>
        </Grid.Resources>
<!-- more code here -->
  <esri:GraphicsLayer ID="MyGraphicsLayer" Graphics="{Binding Source={StaticResource obj}, Path=Graphics, Mode=TwoWay}" >

Code-behind:

            MyViewModelObject obj = new MyViewModelObject();
            GraphicsLayer layer = this.MyMap.Layers["MyGraphicsLayer"] as GraphicsLayer;
            System.Windows.Data.Binding binding = new System.Windows.Data.Binding("Graphics");
            binding.Source = obj;
            binding.Mode = System.Windows.Data.BindingMode.TwoWay;
            System.Windows.Data.BindingOperations.SetBinding(layer, GraphicsLayer.GraphicsProperty, binding);

Either way will let you modify the elements in your Map's GraphicsLayer.

            obj.Graphics.Add(new Graphic() { Geometry = new MapPoint(17, 15) });