public SpatialQueryFilter()

public async Task SearchingAFeatureClass()
{
  await ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
  {
    using (Geodatabase geodatabase = new Geodatabase(new DatabaseConnectionFile(new Uri("path\\to\\sde\\file\\sdefile.sde"))))
    using (FeatureClass schoolBoundaryFeatureClass = geodatabase.OpenDataset<FeatureClass>("LocalGovernment.GDB.SchoolBoundary"))
    {
      // Using a spatial query filter to find all features which have a certain district name and lying within a given Polygon.
      SpatialQueryFilter spatialQueryFilter = new SpatialQueryFilter
      {
        WhereClause = "DISTRCTNAME = 'Indian Prairie School District 204'",
        FilterGeometry = new PolygonBuilderEx(new List<Coordinate2D>
        {
          new Coordinate2D(1021880, 1867396),
          new Coordinate2D(1028223, 1870705),
          new Coordinate2D(1031165, 1866844),
          new Coordinate2D(1025373, 1860501),
          new Coordinate2D(1021788, 1863810)
        }).ToGeometry(),

        SpatialRelationship = SpatialRelationship.Within
      };

      using (RowCursor indianPrairieCursor = schoolBoundaryFeatureClass.Search(spatialQueryFilter, false))
      {
        while (indianPrairieCursor.MoveNext())
        {
          using (Feature feature = (Feature)indianPrairieCursor.Current)
          {
            // Process the feature. For example...
            Console.WriteLine(feature.GetObjectID());
          }
        }
      }
    }
  });
}