Using ArcGIS Desktop 10.2.2, Advanced license. I created a new coded domain for a string field. I added the domain to an existing field. When I edit the features, i would expect to get a list of the coded values from the domain as a dropdown menu. This is not happening. What am I missing - is there a simple check mark or radio button setting?
Make sure subtypes have not been defined for one of the fields in the feature class you are assigning a domain to. In the Feature Class Properties, choose "Subtypes". If a subtype field has been defined, click into each row in the table "Subtypes" and add the domain in the table "Default Values and Domains" below. A dropdown menu will appear only for the features belonging to one of the subtypes for which you have added the domain.
If your feature class contains subtypes, it is not enough to see the domain assigned to the correct field in the "Fields" tab of the Feature Class Properties.
maffa's answer can be carried out programmatically using the optional 'subtype_code' parameter of arcpy.AssignDomainToField_management() where (all) the subtype codes and descriptions can be given as a list of strings e.g. ["0: Unknown", "1: Concrete", "2: Asphalt"]