You can take the union of each FeatureSet.Features.Geometry.Extent and zoom to this resulting extent.
FeatureSet featureSet = args.FeatureSet;
if (featureSet != null && featureSet.Features.Count > 0)
{
ESRI.ArcGIS.Client.Geometry.Envelope env = new ESRI.ArcGIS.Client.Geometry.Envelope();
foreach (Graphic feature in featureSet.Features)
{
env = env.Union(feature.Geometry.Extent);
feature.Symbol = LayoutRoot.Resources["ResultsFillSymbol"] as FillSymbol;
graphicsLayer.Graphics.Insert(0, feature);
}
//ResultsDisplay.Visibility = Visibility.Visible;
MyMap.ZoomTo(env);
}
if (featureSet != null && featureSet.Features.Count > 0)
{
Envelope env = null;
foreach (Graphic feature in featureSet.Features)
{
if (env == null)
env = feature.Geometry.Extent;
else
env.Union(feature.Geometry.Extent);
feature.Symbol = LayoutRoot.Resources["MySymbol"] as SimpleFillSymbol;
graphicsLayer.Graphics.Insert(0, feature);
}
MyMap.ZoomTo(env);
}