How do I override this class property? [duplicate] - ios

Question

This question already has answers here:
Overriding a stored property in Swift
(14 answers)
Closed 5 years ago.
struct SectionData {
var items : [LiveCellObjectProtocol]
var title: String? = nil
subscript(index: Int) -> LiveCellObjectProtocol {
return items[index]
}
}
extension SectionData{
init(title: String? = nil){
self.title = title
self.items = []
}
}
class LiveCellTableViewController: UIViewController {
var sections: [SectionData] = {
return [SectionData(title: "aaa"), SectionData(title: "bbb"), SectionData(title: "ccc")]
}()
}
How do I override sections if I subclass this? I'd like to change the titles.
This doesn't build.
class SomeChild: LiveCellTableViewController {
override var sections: [SectionData] = {
return [SectionData(title: nil), SectionData(title: "Mutual"), SectionData(title: "Connections")]
}()
}

Answer 1

An override property cannot be a stored property. That's just the way Swift works (and this makes sense if you think about it). I list the possibilities in my book as follows:
If the superclass property is writable (a stored property or a computed property with a setter), the subclass’s override may consist
of adding setter observers to this property.
Alternatively, the subclass’s override may be a computed property. In that case:
If the superclass property is stored, the subclass’s computed
property override must have both a getter and a setter.
If the superclass property is computed, the subclass’s computed
property override must reimplement all the accessors that the
superclass implements. If the superclass property is read-only (it has
just a getter), the override can add a setter.
So the way to do what you want to do here is to override, not the property, but the class's initializer. Here's a highly simplified example:
class C {
var sections : [Int] = [1,2,3]
}
class CC : C {
override init() {
super.init()
super.sections = [4,5,6]
}
}
C().sections // [1,2,3]
CC().sections // [4,5,6]

Answer 2

You can't override a stored property in swift. You can use private storage and calculated properties to work around the issue. Something like this:
//: Playground - noun: a place where people can play
import Cocoa
struct SectionData {
let title: String
}
class ParentClass {
private let defaultSections = [SectionData(title: "Parent")]
var sections: [SectionData] {
return defaultSections
}
}
class ChildClass: ParentClass {
private let childSections = [SectionData(title: "Child")]
override var sections: [SectionData] {
return childSections
}
}
// If you wanted a child who appends sections
class AnotherChildClass: ParentClass {
private let childSections = [SectionData(title: "Child")]
override var sections: [SectionData] {
return super.sections + childSections
}
}
Also, because in your example you're just overriding the parent class functionality and your property is immutable, you could just make it a parameter passed in during init.
//: Playground - noun: a place where people can play
import Cocoa
struct SectionData {
let title: String
}
class ParentClass {
let sections: [SectionData]
init(sections: [SectionData]) {
self.sections = sections
}
}
class ChildClass: ParentClass {
}
let parent = ParentClass(sections: [SectionData(title: "Parent")])
let child = ChildClass(sections: [SectionData(title: "Child")])

Answer 3

Get rid of the equals signs:
var sections: [SectionData] {
return [SectionData(title: "aaa"), SectionData(title: "bbb"), SectionData(title: "ccc")]
}
That's why Xcode wanted parentheses. With the equals sign, your code block was defining an inline function, and the () calls the function, using the result to initialize your variable. Without the () you're trying to assign a function to an array.
Without the =, you're defining a property with a getter, which (I assume) is what you want.

Answer 4

Just change the value in your subclass after you create it, if you're loading it from a storyboard, the easiest place is in awakeFromNib:
class SomeChild: LiveCellTableViewController {
override func awakeFromNib() {
super.awakeFromNib()
sections = [SectionData(title: nil), SectionData(title: "Mutual"), SectionData(title: "Connections")]
}
}