Highlight all features associated with selected feature via relationship in ArcObjects C#

Question

I am trying to highlight those features which are associated (via Relationship) to the selected feature in ArcObjects C#.

public void IRelationship_Example(IFeature feature)
{
    //assumes that only one RelationshipClass exists for the Origin feature class
    IEnumRelationshipClass enumRelClass = feature.Class.get_RelationshipClasses(esriRelRole.esriRelRoleAny);
    IRelationshipClass relClass = enumRelClass.Next();
    //if a feature with no Relationships established has been selected, exit
    if (relClass == null)
    {
        return;
    }
    ESRI.ArcGIS.esriSystem.ISet relSet = relClass.GetObjectsRelatedToObject((IObject)feature);
    relSet.Reset();
    //If an Attributed Relationship does not exist, exit
    if (relClass.IsAttributed != true)
    {
        return;
    }
    IFeature destinationFeature = (IFeature)relSet.Next();
    while (destinationFeature != null)
    {
        IRelationship relationship = relClass.GetRelationship((IObject)feature, (IObject)destinationFeature);
        IRow row = (IRow)relationship;
        object attributeValue;
        if (row.get_Value(0) == null)
        {
            attributeValue = "0";
        }
        else
        {
            attributeValue = row.get_Value(0);
        }
        MessageBox.Show("Destination OID: {0}  Origin OID:  {1}  Attribute value:  {2}", relationship.DestinationObject.get_Value(0), relationship.OriginObject.get_Value(0), attributeValue);
        destinationFeature = (IFeature)relSet.Next();
    }
} 

I am newbie in ArcGIS Products.

As shown in above image, once, I select the feature, I can able to highlight all associated features.

For selecting feature I am using following Code:

newselection = true;  //set newselection to true on every mouse click.
HighlightClickedFeature(Layer, 22, activeView);

private void HighlightClickedFeature(IFeatureLayer layer, int featureOid, IActiveView activeView)
{
        IFeatureClass featureClass = layer.FeatureClass;
        IFeature feature = featureClass.GetFeature(featureOid);
        IGeometry geometry = feature.Shape;

        ISpatialFilter spatialFilter = new SpatialFilter();
        spatialFilter.Geometry = geometry;
        spatialFilter.GeometryField = featureClass.ShapeFieldName;
        spatialFilter.SpatialRel = esriSpatialRelEnum.esriSpatialRelIntersects;
        spatialFilter.WhereClause = "OBJECTID = " + featureOid;

        IFeatureSelection featureSelection = layer as IFeatureSelection;
        if (featureSelection != null)
        {
            if (newselection == true)
            {
                //featureSelection.Add(feature);
                //featureSelection.CombinationMethod = esriSelectionResultEnum.esriSelectionResultAdd;
                //featureSelection.SelectionSet.Combine(selectionSet, esriSetOperation.esriSetUnion, selectionSet2);
                featureSelection.SelectFeatures(spatialFilter, esriSelectionResultEnum.esriSelectionResultNew, false);
                newselection = false;
            }
            else
            {
                featureSelection.SelectFeatures(spatialFilter, esriSelectionResultEnum.esriSelectionResultAdd, false);
            }
            activeView.Refresh();
        }
    }

Answer 1

Things like feature selection on the map and highlights happen at the layer level, not the feature class level. So while you can identify the features in the relationship class, you'll need to go to find the associated layers on your map and select the features through there. You can loop through the layers like this:

public IEnumerable<IFeatureLayer> GetLayers()
{
    var layer_enum = (ArcMap.Document as IMxDocument).FocusMap.Layers;
    ILayer layer;
    while ((layer = layer_enum.Next()) != null)
        if (layer.Valid && layer is IFeatureLayer)
            yield return layer as IFeatureLayer;
}

I'm not very familiar with relationship classes, but you'll want to at least look for a a feature layer that has the FeatureClass property as the feature class you're looking for.

Layers can also have definition queries that can limit which features are visible on that layer, such as a layer for only one particular subtype. You may need to check the definition query as well as that might filter out the features you're trying to highlight.

To then select the features you can cast the layer to IFeatureSelection and then use the Add or SelectFeatures functions to select all your features.

//remove previous selection
(ArcMap.Document as IMxDocument).FocusMap.ClearSelection();

//Add method
IFeature feature;
IFeatureLayer layer;
(layer as IFeatureSelection).Add(feature);

//SelectFeatures method
IFeatureLayer layer;
List<int> oids;
IQueryFilter filter = new QueryFilter();
filter.WhereClause = $"{layer.FeatureClass.OIDFieldName} IN ({String.Join(",", oids)})"
(layer as IFeatureSelection).SelectFeatures(filter, esriSelectionResultEnum.esriSelectionResultNew, false);