How to Remove Items from a DataGrid Bound to an ObservableCollection?

RussCoffey

How do I remove items from a DataGrid bound to an ObservableCollection?  I can remove items from the ObservableCollection, but the DataGrid does not update.  (And I might more correcly phrase the question as "how do I properly bind a DataGrid to an ObservableCollection to realize full functionality of interaction with the DataGrid"?)  Here is the background.

Step 1: Allow the user to select line features, which are then displayed as graphics in a graphicslayer and attribute information in a DataGrid.
Solution: The "Spatial Query" sample code did this quite nicely.

Step 2: Allow the user to keep working with the selection set, adding/removing records. 
My solution that doesn't work yet: Write the results of the QueryTask into an ObservableCollection and alter the binding of the DataGrid to be the ObservableCollection instead of the QueryTask results.

My solution for Step 2 works well for performing the SpatialQuery repeatedly and adding new rows to the DataGrid.  I can remove graphics and items from the ObservableCollection (verified by checking the Count property after each delete), but I cannot tell why the DataGrid will not recognize deletes.

Thanks for any help or suggestions.

.........j.russ


Here is my code as it currently stands, and I realize that I probably have a few crossed wires at this point.


  private void MyDrawSurface_DrawComplete(object sender, ESRI.ArcGIS.Client.DrawEventArgs args)
  {

   QueryTask queryTask = new QueryTask("http://arcserverdev/arcgis/rest/services/ETS/Record_Drawing_Request/MapServer/5");
   queryTask.ExecuteCompleted += QueryTask2_ExecuteCompleted;
   queryTask.Failed += QueryTask2_Failed;

   Query query = new ESRI.ArcGIS.Client.Tasks.Query();
   query.OutSpatialReference = MyMap.SpatialReference;

   // Specify fields to return from query
   query.OutFields.AddRange(new string[] { "INSTALLPROJID", "IDFEATURE", "DIAMETER", "MATERIAL" });
   query.Geometry = args.Geometry;

   // Return geometry with result features
   query.ReturnGeometry = true;

   queryTask.ExecuteAsync(query);

  }


  private void QueryTask2_ExecuteCompleted(object sender, ESRI.ArcGIS.Client.Tasks.QueryEventArgs args)
  {
   FeatureSet featureSet = args.FeatureSet;
   GraphicsLayer graphicsLayer = MyMap.Layers["MySelectionGraphicsLayer"] as GraphicsLayer;

   if (featureSet == null || featureSet.Features.Count < 1)
   {
    MessageBox.Show("No features returned from query");
    return;
   }

   if (first_spatial_query)
   {
    _thisgrid.Clear(); //Should already be empty anyway
    Binding resultFeaturesBinding = new Binding("LastResult");
    resultFeaturesBinding.Source = _thisgrid;
    resultFeaturesBinding.Mode = BindingMode.TwoWay;
    QueryDetailsDataGrid.SetBinding(DataGrid.ItemsSourceProperty, resultFeaturesBinding);
    QueryDetailsDataGrid.ItemsSource = _thisgrid;

////I realize that this next block of code overwrites/undoes some of the previous lines of code, but these are the lines that allow the graphics and the DataGrid to be in sync (and obviously I am still experimenting).
    QueryDetailsDataGrid.Columns.Clear();
    QueryDetailsDataGrid.ItemsSource = featureSet;  // featureSet.Features;
    foreach (KeyValuePair<string, string> kv in featureSet.FieldAliases)
    {
     DataGridTextColumn dataGridColumn = new DataGridTextColumn();
     Binding b = new Binding("Attributes");
     b.Converter = new DictionaryConverter();
     b.ConverterParameter = kv.Key;
     dataGridColumn.Binding = b;
     dataGridColumn.Header = kv.Value;
     QueryDetailsDataGrid.Columns.Add(dataGridColumn);
    }

    first_spatial_query = false;
   }

   if (featureSet != null && featureSet.Features.Count > 0)
   {
    foreach (Graphic feature in featureSet.Features)
    {
     feature.Symbol = LayoutRoot.Resources["ResultsLineSymbol"] as LineSymbol;
     graphicsLayer.Graphics.Insert(graphicsLayer.Graphics.Count, feature);
     PipeItem newrow = new PipeItem(feature.Geometry as ESRI.ArcGIS.Client.Geometry.Polyline, feature.Attributes["INSTALLPROJID"].ToString(), feature.Attributes["IDFEATURE"].ToString(), feature.Attributes["DIAMETER"].ToString(), feature.Attributes["MATERIAL"].ToString());
     _thisgrid.Add(newrow);
    }
    //MessageBox.Show(graphicsLayer.Graphics.Count + " graphics created.");
    ResultsDisplay.Visibility = Visibility.Visible;

   }

   MyDrawSurface.IsEnabled = false;
  
  }


Here is one of the points where I am trying to remove a record from the DataGrid (any record at this point - I am currently just trying to remove the first one in the list).

  private void GraphicsLayer_MouseEnter_DeleteRecords(object sender, GraphicMouseEventArgs args)
  {
   //The next two lines work fine for removing the graphic
   GraphicsLayer selectionGraphicslayer = MyMap.Layers["MySelectionGraphicsLayer"] as GraphicsLayer;
   selectionGraphicslayer.Graphics.Remove(args.Graphic);
     //The next line removes a record from the ObservableCollection, but does nothing to the DataGrid.
   _thisgrid.RemoveAt(0);
  }


And finally, here is my ObservableCollection:

public class PipeGrid : ObservableCollection<PipeItem>
{
}

public class PipeItem
{
  private ESRI.ArcGIS.Client.Geometry.Polyline geom;
  private string projid;
  private string idf;
  private string dia;
  private string mat;

  public PipeItem(ESRI.ArcGIS.Client.Geometry.Polyline GEOM, string ProjID, string IDF, string DIA, string MAT)
  {
   this.GEOMETRY = GEOM;
   this.IDFEATURE = IDF;
   this.INSTALLPROJID = ProjID;
   this.DIAMETER = DIA;
   this.MATERIAL = MAT;
  }

  public ESRI.ArcGIS.Client.Geometry.Polyline GEOMETRY
  {
   get { return geom; }
   set { geom = value; }
  }
  public string INSTALLPROJID
  {
   get { return projid; }
   set { projid = value; }
  }
  public string IDFEATURE
  {
   get { return idf; }
   set { idf = value; }
  }

  public string DIAMETER
  {
   get { return dia; }
   set { dia = value; }
  }
  public string MATERIAL
  {
   get { return mat; }
   set { mat = value; }
  }
}

JenniferNery

The key here is to assign the DataGrid's ItemsSource once through Binding to an instance of your ObservableCollection and manipulate this collection instead of re-assigning the DataGrid's ItemsSource because that will defeat the purpose of Binding.

In your XAML, you can create an instance of your PipeGrid or simply use esri's GraphicCollection.

  <Grid x:Name="LayoutRoot" Background="White">
  <Grid.Resources>
   <esri:GraphicCollection x:Key="MyGraphicCollection"/>
  </Grid.Resources>
<!-- more code goes here -->
     <slData:DataGrid x:Name="QueryDetailsDataGrid" ItemsSource="{Binding Source={StaticResource MyGraphicCollection}}"
<!-- more code goes here -->

In the code-behind, you can grab the instance of your ObservableCollection and update them after the query has completed.

        public MainPage()
        {
            InitializeComponent();
            myGraphics = this.LayoutRoot.Resources["MyGraphicCollection"] as GraphicCollection;
        }
        GraphicCollection myGraphics;
        void QueryTask_ExecuteCompleted(object sender, ESRI.ArcGIS.Client.Tasks.QueryEventArgs args)
        {
            FeatureSet featureSet = args.FeatureSet;
            if (featureSet != null && featureSet.Features.Count > 0)
            {
                if (myGraphics != null)
                {
                    myGraphics.Clear();
                    foreach (Graphic g in featureSet.Features)
                        myGraphics.Add(g);
                }
            }
        }

This way anytime you remove a graphic from myGraphics, the DataGrid updates itself.