Need technical advice about passing data through UINavigationController - ios

Question

First of all a small introduction, im relatively new to Swift and to programming in general, been doing it for the last year and loving every and each new thing of this vast world.
My post is about some technical advices and to know if the decisions that are being made in my company make some sense.
I will first address the design that is being suggested and next my conclusions.
The design that's being implemented;
We are working in a big app, this app has some flows where they follow a sequence of 5 to 8 controllers, our team leader insists in this design pattern;

Let’s call the first controller a holder and the holder(black border) is responsible to have a container, this container has a proper navigation controller(red border), also, the holder hold all the data(orange) that those secondary controllers are generating.
Diagram of what this pattern is trying to achieve
To do this every red border controller has a method:

private func getParent() -> HolderViewController? {
if let parent = navigationController?.parent as? HolderViewController {
return parent
}
return nil
}
And to write in holder we call the method;
getParent().someModelInstance.someModelProperty = "some data”
Conclusion;
Passing data through navigation controller seems to go against to the single responsibility principle.
Creating strong references in every controller, even if I ensure that the navigationController is properly deinit when flow ends, does not seem a good option, this could lead to memory leaks and retain cycles.
I cannot ensure that, for some hod reason, two controllers try to access the same property at the same time.
This seems the Singleton Design pattern but with a limited “scope”
Resolutions;
Since I am new and I’m working in a company, and, every company has a hierarchy my objective above all is to learn if my conclusions are wrong and have better and more concise explanation about this.
First of all, to address the problem of memory leaks I created a concurrentQueue.
Instead of accessing the model directly to write in it I tried to address it through a method that will use a keyPath instead of the model directly, this is the method I’m using to write in the model;
In holder:
class HolderViewController: UIViewController {
#IBOutlet weak var bottomNavigationContainer: UIView!
private var bottomNavigationController: UINavigationController!
private var someModel: SomeModel!
private let concurrentQueue: DispatchQueue = DispatchQueue(label: "concurrentQueue", attributes: .concurrent)
override func viewDidLoad() {
super.viewDidLoad()
setupBottomNavigation()
}
private func setupBottomNavigation() {
rootController = SecondayViewController()
if let root = rootController {
bottomNavigationController = UINavigationController(rootViewController: root)
addChild(bottomNavigationController)
bottomNavigationController.view.frame = bottomNavigationContainer.bounds
bottomNavigationContainer.addSubview(bottomNavigationController.view)
}
}
}
extension HolderViewController {
public func setValueInModel<Value>(_ value: Value, forKey path: WritableKeyPath<SomeModel, Value>) {
concurrentQueue.async(flags: .barrier) { [weak someModelInstance] in
if var obj = someModelInstance {
obj[keyPath: path] = value
}
}
}
public func readFromHolder() -> SomeModel {
concurrentQueue.sync {
return self.someModelInstance
}
}
}
This methods will be called like this;
class SecondayViewController: UIViewController {
var someString: String = "some data"
private func getParent() -> HolderViewController? {
if let parent = navigationController?.parent as? HolderViewController {
return parent
}
return nil
}
private func setValueInHolder(string: String) {
getParent().setValueInModel(string, forKey: \.someModelProperty)
}
private func readFromHolder() -> String {
return getParent().readFromHolder().someModelProperty
}
}
This look like some messy code to do a simple thing, we could use closures, delegates, segues etc… but my team leader does not like the other, simpler and more common solutions. Forgot to mention, every of our controllers has a xib and we do not use storyboards.
I know the basics of how to use the other options, what I’m trying is to understand if this is or it isn’t a good solution and why, and if my way of thinking and my methods make any sense.
Remember, every conclusion I took or every solution I've implemented could be wrong, that’s why I’m sharing with you my thoughts in order to learn from your advices and experience
Thanks in advance. :)
Stay safe!

Answer 1

As a preface: this type of question may be more fitting for the code review community
I can tell just by looking at the first diagram where your concern starts. Seeing the data flow as a graph you notice that there is a cycle. There is a time an a place where this may be use full (for performance more than anything) and memory management is extremely important to keep in mind in that case.
You may notice that after the call to addChild(_:) adds the contained controller to children: [UIViewController] and sets its parent property. But this done for you by the library.
Similar to the concept of the ViewController where views are dumb and the logic is contained in the view controller. I would similarly decouple the children from the parent view controllers moving most of the logic away from the children and coupling using the appropriate mechanism.
With that said I rarely find much value in using KVO with swift there are other mechanism that accomplish the same thing.
It really does depend on what the relationships are between the controllers are and what functions they have. There isn't much there to go off of. I'll leave that up to you to discover what solution you really need and the best guidance I found for this was on NSHipster's blog describing the communication mechanism to use for loose/strong coupling vs one-to-one and one-to-many relationships.
Also should point out that:
if let root = rootController {
bottomNavigationController =
UINavigationController(rootViewController: root)
addChild(bottomNavigationController)
bottomNavigationController.view.frame =
bottomNavigationContainer.bounds
bottomNavigationContainer.addSubview(bottomNavigationController.view)
}
You should be using willMove and didMove and move any set up there.