Difference between SOLIDWORKS API Methods and Interfaces with and without "I"

There are two versions of methods, properties, and objects (interfaces) in the SOLIDWORKS API:

• Those starting with I (e.g. ISldWorks, IModelDoc2, IAnnotation, ISldWorks::IActiveDoc)
• Those without I (e.g. SldWorks, ModelDoc2, Annotation, SldWorks::ActiveDoc)

These two versions correspond to the same object or method. The main differences are as follows:

• Methods with the "I" prefix do not expose events.

Below is a snapshot of available events for a variable declared with SldWorks. Available events:

{ width=250 }

Below is a snapshot of available members for a variable declared with ISldWorks. No events available:

{ width=250 }

• Methods with the "I" prefix typically return a type-safe version of the interface instead of an object or IDispatch. This means that explicit casting is not required in type-safe languages (e.g. C#) at compile time:

ISldWorks app;
...
IModelDoc2 model = app.IActiveDoc; // Correct
IModelDoc2 model = app.ActiveDoc; // Compilation error
IModelDoc2 model = app.ActiveDoc as IModelDoc2; // Correct