Making ViewController slimmer by moving TableView away

Question

I am quite new into programming and facing some issues while trying to slim down my ViewController by moving creation of the tableView and associated views to the separate class and moving delegates and datasource from VC to separate one.

My constellation of current files and work is as follows:

After network connection, when data are received, I am calling inside a closure class to set view which will have embedded UITableView.
Fetched data are being saved into the CoreData stack

I instantiate view from another class

var detailView: DetailView! { return self.view as? DetailView }

Once I will download first part of the UI (separate call which works fine)

I am moving onto the part which is messy and surpass my abilities

I call a function createReposCard()

        dispatchGroup.notify(queue: dispatchQueue) {
            DispatchQueue.main.async {

                // slide animation
                UIView.animate(withDuration: 0.75, delay: 0.5, usingSpringWithDamping: 0.9, initialSpringVelocity: 0.0, options: [], animations: {
                    self.detailView.reposCard.center = CGPoint(x: self.detailView.reposCard.center.x, y: self.detailView.reposCard.center.y-UIScreen.main.bounds.height)
                }, completion: nil)
                self.detailView.createReposCard(for: self.repos)
                self.detailView.detailsTableView.reloadData()
                self.activityIndicator.stopAnimating()
                self.activityIndicator.removeFromSuperview()
            }
        }

Code is incomplete to depict the problem only, but what it does one by one. I am passing info about selected user (irrelevant info) then I am making a reference to my DetailsViewController which still e.g. holds CoreData stack

In initializer I am instantiating detailsViewController and passing it onto the class which holds delegates (I am passing it to have there reference to the CoreData)

class DetailView: UIView {


    var selectedUser: User?


    var detailsViewController: DetailsViewController!


    let detailsTableView: UITableView = {
        let tableView = UITableView()
        tableView.frame = CGRect.zero
        tableView.register(UITableViewCell.self, forCellReuseIdentifier: "reposCell")
        return tableView
    }()

init(selectedUser:User, frame: CGRect) {
        super.init(frame: frame)
        self.selectedUser = selectedUser

        detailsViewController = DetailsViewController()
        let tableViewDelegates = TableViewDelegates(detailsViewController: detailsViewController)
        detailsTableView.delegate = tableViewDelegates
        detailsTableView.dataSource = tableViewDelegates
    }

And finally code jumps into the depicted class where I am knocked down by "Unexpectedly found nil while implicitly unwrapping..."

public class TableViewDelegates: NSObject, UITableViewDataSource,UITableViewDelegate {

    private let detailsViewController: DetailsViewController

    init(detailsViewController: DetailsViewController){
        self.detailsViewController = detailsViewController
        super.init()
    }

   public func numberOfSections(in tableView: UITableView) -> Int {
        return detailsViewController.fetchedResultsController.sections?.count ?? 1

    }
...

Actually I don't know if my concept is good as I feel quite lost, but my intentions were as follows:

Move View creation to other class
Move TableView delegates to other class Finally - move networking and CoreData to other class.

But as I see, simple data passing is overcoming my abilities.

score 2 · Answer 1 · answered Aug 22 '19 at 16:04

I think this question can be divided into two parts:

1) Why is my variable nil when I unwrap it?

I don't think we have enough information to answer this accurately, but my overall approach would be like this:

Check what nil variable is being unwrapped;
Make sure this variable is being properly initialized;
Make sure that the object is not being incorrectly deinitialized;
If you're using Storyboard, use the inspectors to check if everything is set correctly.

There's a particular observation about step 2: you should check the order of execution of your methods to make sure that the variable is properly initialized. Why am I emphasizing this? Because there's a chance that some view (e.g., detailView) is initialized like an ordinary UIView, and then you try to access an element that is not part of a UIView object (e.g., a table view). In other words, check if you're setting the custom views before you try to access them.

2) How to structure the project in a more organized way?

This is a more interesting question, and I think that choosing a better approach will help you to avoid issues like what you're experiencing. I will divide this into some topics. Everything here is my personal opinion and doesn't necessarily reflect the best approach, especially because "best" is subjective here.

PersistenceManager class

First, passing a reference of a view controller to another class just to access CoreData doesn't seem like a good option. A better approach would be to have a PersistenceManager class, for example. You could use an object of this class to fetch and save data. You could pass this object instead of the view controller.

In some architectures (e.g., VIPER), it wouldn't be correct for the view controller to access the persistence directly, so it would be more appropriate to pass an array of already fetched objects. For example:

class TableViewController {
    private let tableView: UITableView!
    private var currentlyDisplayedUsers: [Users]?

    func displayUsers(_ users: [Users]) {
        self.currentlyDisplayedUsers = users
        self.tableView.reloadData()
    }
}

In the example above, the tableView would display currentlyDisplayedUsers, which would be updated by the method displayUsers, which would be called by someone else, like a Presenter.

Network class

Second, I think you should have a network class to download data from the internet. You would use instances of the Network class in the application logic. In other words, you would have something like

// This is in the application logic
// In MVC, the logic is in the Controller, while in VIPER the logic is in the Interactor
class ApplicationLogic {
    let networkAPI: Network?

    ...

    func fetchUserData() {
        networkAPI?.fetchUsers() { data, error in
            // Update the UI based on the response
            // Using the previous example, you could call displayUsers here
        }
    }
}

TableView, TableViewDelegate, and TableViewDataSource

Finally, how to organize these guys. UITableViewDelegate is responsible for telling us about events in the table, while UITableViewDataSource is responsible for filling the table with data, which means that both are strongly related to the table view itself. That said, imho, both should be implemented in different swift files, but as extensions of the view controller that has a reference to the table view. Something like

// TableViewController+UITableViewDelegate.swift
extension TableViewController: UITableViewDelegate {
    ...
}

// TableViewController+UITableViewDataSource.swift
extension TableViewController: UITableViewDataSource {
    ...
}

Using this approach, the delegate and the data source would have access to the users array, mentioned earlier. Here is an example of how to implement a similar approach using VIPER.

So, I hope I could provide a basic idea on these topics. If you want to understand more about how to structure your code, I suggest researching iOS design patterns and architectural patterns. Some architectural design patterns that are famous in iOS development are MVC, MVP, MVVM, and VIPER.

Making ViewController slimmer by moving TableView away

1 Answers1

1) Why is my variable nil when I unwrap it?

2) How to structure the project in a more organized way?