是否可以在Swift中为协议实例设置观察者（KVO）

Question

Hi so I have a protocol called DTNavigationControllerDataSource which is defined as (leaving out the methods)

protocol DTNavigationControllerDataSource: NSObjectProtocol

Then, in my own custom UINavigationController subclass I have an instance variable of this protocol as follows.

var dataSource: DTNavigationControllerDataSource?

Basically I need to know when an object becomes the dataSource. ie The dataSource property is set. So I can call the dataSource when it is initially set, to setup some state. I've thought about using KVO however NSObjectProtocol doesn't define any methods for doing so. I'm not sure if this is even possible or if there is an alternative way outside of using KVO to know when the dataSource property inside DTNavigationController is set. I've also tried didSet and willSet but Xcode threw errors at me, as I think that is only available for primitives.

Answer 1

The didSet approach should work fine actually, had no issue with the following code in a playground (Xcode 7 GM):

class DTNavigationController : UINavigationController {
    var dataSource: DTNavigationControllerDataSource? {
        didSet {
            print("new data source: \(dataSource)")
        }
    }
}