在 Swift 中子类化 NSObject - 初始化器的最佳实践

Question

Here is the layout of an example Class, can someone guide me on what's best practice when creating a subclass of NSObject?

class MyClass: NSObject {

    var someProperty: NSString! = nil

    override init() {
        self.someProperty = "John"
        super.init()
    }

    init(fromString string: NSString) {
        self.someProperty = string
        super.init()
    }

}

Is this correct, am I following best practice here?

I wonder if I'm correctly setting up the initializers (one that sets the string to a default, and one which I can pass in a string)?

Should I call super.init() at the end of each of the initializers?

Should my more specific (the one that takes a string) initializer simply call self.init() at the end rather than super.init() ?

What is the right way to set up the initializers in Swift when subclassing NSObject ? - and how should I call the super init ?

This question (albeit in Objective C) suggests you should have an init, which you always call and simply set the properties in more specific inits: Objective-C Multiple Initialisers

Answer 1

I'm not Swift ninja but I would write MyClass as:

class MyClass: NSObject {
    
    var someProperty: NSString // no need (!). It will be initialised from controller 
    
    init(fromString string: NSString) {
        self.someProperty = string
        super.init() // can actually be omitted in this example because will happen automatically.
    }
    
    convenience override init() {
        self.init(fromString:"John") // calls above mentioned controller with default name
    }        
}

---

See the initialization section of the documentation

Answer 2

If someProperty can be nil, then I think you want to define the property as:

var someProperty: NSString?

This also eliminates the need for a custom initializer (at least, for this property), since the property doesn't require a value at initialization time.

Answer 3

In complement to the answers, a good idea is to call super.init() before other statements. I think it's a stronger requirement in Swift because allocations are implicit.