Handle UIView common initialization in swift - ios

Question

Some special classes like UIView have more than one designated initializer.
In Objective-X, we could factor common initialization into a separate function
- (id)initWithCoder:(NSCoder *)aDecoder {
if (self = [super initWithCoder:aDecoder]) {
[self initialize];
}
return self;
}
- (id)initWithFrame:(CGRect)frame {
if (self = [super initWithFrame:frame]) {
[self initialize];
}
return self;
}
In Swift this is no longer a possibility because the following code results 'self used before super.init call'
override init(frame: CGRect) {
self.initialize()
super.init(frame: frame)
}
required init(coder aDecoder: NSCoder) {
self.initialize()
super.init(coder: aDecoder)
}
Placing self.initialize after super.init is no help, either, since my entire purpose is initializing members. The following would result in 'property self.X not initialized at super.init call'
var X : Int
override init(frame: CGRect) {
super.init(frame: frame)
self.initialize()
}
required init(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
self.initialize()
}
What should i do if i want to factor common initialization in this case? Note that i specifically do not want to use awakeFromNib because i want my objects to be available in any related awakeFromNib implementations in my object hierarchy. Note also that optionals do not make sense for my use case.

Answer 1

The obvious answer is to call initialize after calling super.init:
override init(frame: CGRect) {
super.init(frame: frame)
self.initialize()
}
However, you probably have some instance variables that you want to initialize in the initialize method. The facts are these:
You must initialize all member variables before calling super.
You may not call methods on self (or access computed properties on self) before calling super.init.
The inexorable conclusion is that if you have instance variables you want to initialize in initialize, you must declare each such variable with var, not let, and do one of these things:
Give the instance variable a default value:
var name: String = "Fred"
Make the instance variable Optional, and let it be initialized to nil:
var name: String?
Make the instance variable ImplicitlyUnwrappedOptional, and let it be initialized to nil:
var name: String!
My preference at this point is #2 (make it Optional and initialized to nil).

Answer 2

There's a neat solution to this here: https://stackoverflow.com/a/26772103/2420477
Basically, mark your two init functions convenience and then have them call out to a third private init function that has your common initialisation code.
For your case, you could use something like this:
class MyView: UIView {
let X: Int // No need to use an optional, as we assign this in an initializer
enum InitMethod {
case Coder(NSCoder)
case Frame(CGRect)
}
override convenience init(frame: CGRect) { // Marking as convenience let's us call out to another constructor
self.init(.Frame(frame))!
}
required convenience init?(coder aDecoder: NSCoder) { // Marking as convenience let's us call out to another constructor
self.init(.Coder(aDecoder))
}
private init?(_ initMethod: InitMethod) {
// You can put your common initialization code here:
X = 1
switch initMethod {
case let .Coder(coder): super.init(coder: coder)
case let .Frame(frame): super.init(frame: frame)
}
}
}