public class CIMSimpleRenderer : CIMRenderer, System.ComponentModel.INotifyPropertyChanged, System.Xml.Serialization.IXmlSerializable  

public Task SetFeatureLayerSymbolAsync(FeatureLayer ftrLayer, CIMSymbol symbolToApply)
{
  if (ftrLayer == null || symbolToApply == null)
    throw new System.ArgumentNullException();

  return QueuedTask.Run(() =>
  {

    //Get simple renderer from the feature layer
    CIMSimpleRenderer currentRenderer = ftrLayer.GetRenderer() as CIMSimpleRenderer;
    if (currentRenderer == null)
      return;

    //Set symbol's real world setting to be the same as that of the feature layer
    symbolToApply.SetRealWorldUnits(ftrLayer.UsesRealWorldSymbolSizes);

    //Update the symbol of the current simple renderer
    currentRenderer.Symbol = symbolToApply.MakeSymbolReference();
    //Update the feature layer renderer
    ftrLayer.SetRenderer(currentRenderer);
  });
}

public Task SetFeatureLayerSymbolFromStyleItemAsync(
           FeatureLayer ftrLayer, SymbolStyleItem symbolItem)
{
  if (ftrLayer == null || symbolItem == null)
    throw new System.ArgumentNullException();

  return QueuedTask.Run(() =>
  {
    //Get simple renderer from the feature layer
    CIMSimpleRenderer currentRenderer = ftrLayer.GetRenderer() as CIMSimpleRenderer;
    if (currentRenderer == null)
      return;
    //Get symbol from the SymbolStyleItem
    CIMSymbol symbol = symbolItem.Symbol;

    //Set symbol's real world setting to be the same as that of the feature layer
    symbol.SetRealWorldUnits(ftrLayer.UsesRealWorldSymbolSizes);

    //Update the symbol of the current simple renderer
    currentRenderer.Symbol = symbol.MakeSymbolReference();
    //Update the feature layer renderer
    ftrLayer.SetRenderer(currentRenderer);
  });
}