UIKit – loadView vs viewDidLoad

Weak, unowned or sturdy subviews?

I’ve acquired various emails and tweets about this matter, so I made a decision to put in writing 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 suggest 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 should 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 a giant change and Apple additionally touched their inside view administration. Earlier than iOS6 it was a typical observe to outline weak subviews. As a result of they’d a powerful reference to it and so they weren’t releasing it except 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 cause was the addSubview technique. The documentation states that it will create a powerful reference, which mechanically 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 affordable, proper? 🧠

Weak subviews

Properly, the issue is that if you wish to outline a weak variable we now have to make use of an non-compulsory, however I do not like the thought of utilizing an non-compulsory 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 is not going anyplace. It is solely going to be “destroyed” when my view controller is deallocated. Ought to I declare it as an implicitly unwrapped non-compulsory?!? Perhaps.

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 unsuitable with unwrapped weak pointers, as a result of should 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 likely be nil. On this case there will not be any extra sturdy references and your view will likely be deallocated straight away, so if it is an implicitly unwrapped non-compulsory, then we now have a bother. Your app will crash should you attempt to entry the property, as a result of it should have a zero worth.

So sure you should use implicitly unwrapped non-compulsory 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 signifies that you do not belief Apple’s view administration system, which is ok, there will be bugs, however actually that is fairly an important characteristic and it has been round for a decade by now. 🙃

The opposite various is to make use of an everyday weak non-compulsory variable, however in that case you may all the time should test if it is nil or not, which goes to be a ache within the ass, however at the least you are going to be protected for positive. Private opinion: it will not definitely worth the effort in any respect and I by no means saved views like this.

Robust subviews

My suggestion is to belief Apple and outline your subviews as sturdy properties. Okay, this may also be problematic if in case you have different sturdy references to the identical stuff, however generally if the view controller has the one reference to that given subview you have to be completely wonderful.

Since it is a sturdy property you additionally should initialize the view, however that is not a giant 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 an everyday init() technique, that is even higher, becuase you’ll use auto structure for positive and this fashion can set the translatesAutoresizingMaskIntoConstraints property in a single go.

import UIKit

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

        self.translatesAutoresizingMaskIntoConstraints = false
    }
    
    @obtainable(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been carried out")
    }
    
    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 assessments 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 kind of equal, I might say that you just will not have to outline views as unowned references, as a result of they are often problematic if it involves initialization. It is normally higher to have a weak reference and test for nil values, however after all there will be some instances 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, nevertheless it’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 definitely should not name tremendous.loadView().

import UIKit

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

        
            
    }
}

In each different case while you simply wish to add views to the view hierarchy, it is utterly wonderful to name the tremendous technique. I am normally 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 is named. It’s attainable to configure views contained in the loadView technique too, however I want to maintain the hierarchy setup there and I place every part else contained in the viewDidLoad perform. I imply controller associated stuff solely, like organising navigation bar buttons and issues like this.

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

Conclusion

Primarily based on my present data, here’s what I like to recommend for contemporary UIKit builders:

• Outline your subviews as sturdy properties
• At all times test for leaks, implement deinit, use breakpoints or devices
• Use weak / unowned references if you need to break retain cycles
• Add views to the hierarchy within the loadView technique
• Use subclasses for styling views, make them reusable
• Outline structure constraint getters on the view subclass, activate them inside loadView
• Carry out remaining UI associated operations within the viewDidLoad perform

That is it. I am not saying that is the proper strategy, however for me it is positively the best way to go ahead with UIKit. I do know for positive that many individuals are nonetheless working with the framework and it’s right here to remain for a very long time. I hope the following tips will aid you to know UIKit just a bit bit higher. ☺️