Engine中如何实现唯一值渲染时按字段值分组渲染？

IColor color1 = pEnumRamp.Next(); 

ISimpleFillSymbol fillSym1 = new SimpleFillSymbolClass(); 

fillSym1.Color = color1; 

pUniqueValueRenderer.AddValue(1, TYPES, fillSym1 as ISymbol); 

pUniqueValueRenderer.AddReferenceValue(2, 1); 

pUniqueValueRenderer.AddReferenceValue(3, 1); 

pUniqueValueRenderer.set_Label(1, type1); 



IColor color2 = pEnumRamp.Next(); 

ISimpleFillSymbol fillSym2 = new SimpleFillSymbolClass(); 

fillSym2.Color = color2; 

pUniqueValueRenderer.AddValue(4, TYPES, fillSym2 as ISymbol); 

pUniqueValueRenderer.AddReferenceValue(5, 4); 

pUniqueValueRenderer.AddReferenceValue(6, 4); 

pUniqueValueRenderer.set_Label(4, type2); 

​