HiThe link from Nir's reply above seems to have a decent c# example. What problem are you having getting this to do what you want?
public static void CreateFeature(IFeatureClass featureClass, IPolyline polyline)
{
// Build the feature.
IFeature feature = featureClass.CreateFeature();
feature.Shape = polyline;
// Apply the appropriate subtype to the feature.
ISubtypes subtypes = (ISubtypes)featureClass;
IRowSubtypes rowSubtypes = (IRowSubtypes)feature;
if (subtypes.HasSubtype)
{
// In this example, the value of 3 represents the PVC subtype.
rowSubtypes.SubtypeCode = 3;
}
// Initialize any default values the feature has.
rowSubtypes.InitDefaultValues();
// Update the value on a string field that indicates who installed the feature.
int contractorFieldIndex = featureClass.FindField("CONTRACTOR");
feature.set_Value(contractorFieldIndex, "K Johnston");
// Commit the new feature to the geodatabase.
feature.Store();
}