How to quick get all symbols for feature layer with ArcObjects

Question

I have a FeatureLayer and I want to enumerate all the symbols used in it. Simple way - it is to call SymbolByFeature for each features. Something approximately likes:

Dim l as IFeatureLayer
Dim c as IFeatureCursor
Dim r as IFeatureRender
Dim f as IFeature
Dim s as ISymbol

Set r = IGeoFeatureLayer(l).Renderer
Set c = l.Search(0, True)
Set f = c.NextFeature

Do Until f is Nothing
  Set s = r.SymbolByFeature(f)
  [...]  ' check whether this symbol is in collection and add it if necessary
  Set f = c.NextFeature
Loop

The problem with this method is that it too long, especially when there is a lot of features in the feature layer.
Question: Is there a faster way to get a collection of all the symbols in a feature layer?

Answer 1

This is my solution (in C++)

esriCarto::IFeatureLayerPtr l = get_layer(); // it is taken from somewhere
esriCarto::ILegendInfoPtr info = l;

for (long i = 0; i < info->LegendGroupCount; ++i) {
    esriCarto::ILegendGroupPtr group = info->GetLegendGroup(i);

    for (long j = 0; j != group->ClassCount; ++j) {
            esriCarto::ILegendClassPtr c = group->GetClass(j);
            some_function_to_add_symbol(c->Symbol);
    }
}

Answer 2

You could put in if statements to handle each different coclass that implements IFeatureRenderer. e.g. For IUniqueValueRenderer, you can loop through each value, and get the symbol associated with the value. For ISimpleRenderer, just get the single symbol, etc.