以编程方式在Objective-C中创建属性？

Question

How can you create a property in objective-c programmatically?

Background:

• so effectively, based on data you read in from a store, create properties on a class
• specifically I wanted to create some typed properties to represent my "eventtypes" which I store in core data - so whilst the EventTypes are in coredata in the EventTypes entity, I could read them in at run time to a class and then reference them list "EventTypes.ACTIVE_EVENT"

The overall goal I had in mind was:

• keep types in the core data store modelled
• but still have a way to easily access a managed object type instance (eg ACTIVE_EVENT) programmatically via use of the simple property approach .

Answer 1

A regular Objective C property normally causes the compiler to generate code for getters and setters. But an iOS app isn't allowed to add any new executable code due to security sandbox restriction, so at run time you can't programmatically do this the same way as the compiler.

What you can do is use the Objective C runtime to emulate getting and setting a property, perhaps using the forwardInvocation: and methodSignatureForSelector: methods for handling unrecognized messages. The backing property state data could be stored, for instance, in some sort of mutable dictionary of property elements held by the class object. Then the object might act (a bit more slowly) as if it had implemented the property you created programmatically.