UIKit – loadView vs viewDidLoad

Weak, unowned or sturdy subviews?

I’ve bought various emails and tweets about this subject, so I made a decision to jot down about it, as a result of it’s actually laborious to discover a correct reply for this query on the web. There are some nice posts and programming guides, some some articles are a bit older, nonetheless many individuals are asking the weak vs sturdy IBOutlet query even on the official boards, however noone actually explains the explanations, even on the boards they solely advocate this WWDC session video. So what is going on on right here? 🤔

I did a little analysis on the subject and the very very first thing that we must always state is that this: Apple eliminated the viewDidUnload technique in iOS6 and from that model the iOS view controller lifecycle modified a bit. If you do not know a lot in regards to the lifecycle strategies (demystified), it’s best to learn this text. This was fairly an enormous change and Apple additionally touched their inner view administration. Earlier than iOS6 it was a typical follow to outline weak subviews. As a result of that they had a powerful reference to it they usually weren’t releasing it until you eliminated it from the view hierarchy.

This was about 10 years in the past. Now why are we nonetheless afraid of sturdy subviews? The primary motive was the addSubview technique. The documentation states that it will create a powerful reference, which routinely triggered my mind and I outlined my views as weak pointers, since they are going have a powerful reference to their dad and mom. Appears cheap, proper? 🧠

Weak subviews

Nicely, the issue is that if you wish to outline a weak variable we’ve got to make use of an elective, however I do not like the thought of utilizing an elective variable for the reason that view goes to be all the time there, it is a part of the view hierarchy in some unspecified time in the future in, it isn’t going anyplace. It is solely going to be “destroyed” when my view controller is deallocated. Ought to I declare it as an implicitly unwrapped elective?!? Possibly.

import UIKit

class ViewController: UIViewController {

    weak var foo: UILabel! 
    weak var bar: UILabel? 
    
    override func viewDidLoad() {
        tremendous.viewDidLoad()

        
        foo.removeFromSuperview()
        foo.textual content = "crash"
    }
}

Really you possibly can go improper with unwrapped weak pointers, as a result of in the event you take away your view from the view hiearchy in some unspecified time in the future in time earlier than the view controller deallocation then your weak pointer will probably be nil. On this case there will not be any extra sturdy references and your view will probably be deallocated instantly, so if it is an implicitly unwrapped elective, then we’ve got a bother. Your app will crash in the event you attempt to entry the property, as a result of it’ll have a nil worth.

So sure you should utilize implicitly unwrapped elective variables to retailer subviews, however solely in case you are positive that you’re not going to take away it from the hiearchy. This additionally implies that you do not belief Apple’s view administration system, which is ok, there will be bugs, however actually that is fairly an important function and it has been round for a decade by now. 🙃

The opposite different is to make use of a daily weak elective variable, however in that case you will all the time should test if it is nil or not, which goes to be a ache within the ass, however no less than you are going to be protected for positive. Private opinion: it will not well worth the effort in any respect and I by no means saved views like this.

Sturdy subviews

My advice is to belief Apple and outline your subviews as sturdy properties. Okay, this will also be problematic when you’ve got different sturdy references to the identical stuff, however on the whole if the view controller has the one reference to that given subview try to be completely positive.

Since it is a sturdy property you additionally should initialize the view, however that is not an enormous deal. You may all the time initialize a view with a .zero body and that is it. Alternatively you possibly can create a subclass with a daily init() technique, that is even higher, becuase you’re going to use auto format for positive and this manner can set the translatesAutoresizingMaskIntoConstraints property in a single go.

import UIKit

class Label: UILabel {
    
    init() {
        tremendous.init(body: .zero)

        self.translatesAutoresizingMaskIntoConstraints = false
    }
    
    @out there(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been applied")
    }
    
    deinit {
        print("deinit Label")
    }
}

class ViewController: UIViewController {

    
    var foo: Label = .init()
    var bar: UILabel = .init(body: .zero)
    
    override func viewDidLoad() {
        tremendous.viewDidLoad()
        
    }
    
    deinit {
        print("deinit ViewController")
    }
    
}

By implementing a customized deinit technique and even higher, by making a symbolic breakpoint you possibly can simply detect retain cycles and repair reminiscence points. I made some exams and I can affirm you do not have to be afraid of sturdy views, each the viewcontroller and the view goes to be deallocated if it is wanted. 👻

Unowned subviews

Unowned and weak are roughly equal, I might say that you simply will not must outline views as unowned references, as a result of they are often problematic if it involves initialization. It is often higher to have a weak reference and test for nil values, however in fact there will be some circumstances the place you would possibly want an unowned subview reference.

Utilizing loadView and viewDidLoad

The loadView technique can be utilized to create your personal views manually. You need to by no means name this technique immediately, but it surely’s save to override it. The opposite factor that you shouldn’t is that in case you are utilizing this technique to override the foundation view, then you definately should not name tremendous.loadView().

import UIKit

class ViewController: UIViewController {
    
    override func loadView() {
        view = UIView(body: .zero)

        
            
    }
}

In each different case whenever you simply wish to add views to the view hierarchy, it is fully positive to name the tremendous technique. I am often implementing this technique to setup views and constraints.

import UIKit 

class ViewController: UIViewController {

    var foo: Label = .init()
    
    override func loadView() {
        tremendous.loadView()
        
        view.addSubview(foo)
        
        NSLayoutConstraint.activate([
            view.centerXAnchor.constraint(equalTo: foo.centerXAnchor),
            view.leadingAnchor.constraint(equalTo: foo.leadingAnchor),
            view.trailingAnchor.constraint(equalTo: foo.trailingAnchor),
            foo.heightAnchor.constraint(equalToConstant: 44),
        ])
    }
}

This manner I can make sure that each single view is prepared by the point the viewDidLoad technique known as. It’s doable to configure views contained in the loadView technique too, however I desire to maintain the hierarchy setup there and I place every thing else contained in the viewDidLoad perform. I imply controller associated stuff solely, like establishing navigation bar buttons and issues like this.

As I discussed this in my earlier article, I desire to make use of subclasses to configure my views, I additionally transfer format constraints there (as a perform that returns them primarily based on some parameters) to maintain the view controller clear. Contained in the viewDidLoad technique I can carry out extra consumer interface associated actions, however that is it I do not use it for including or styling views anymore.