Why do we need to set delegate to self? Why isn't it defaulted by the compiler?

Question

I think I fully understand the concept of delegation, my question is that when we do:

class someViewController : UIViewController, UITableViewDelega         


        

Answer 1

would it ever be possible that we wouldn't want to set tableView.delegate to self

Yes, if you would implement datasource and delegate in it's own class.

why is Xcode forcing us to do some extra work here?

to allow as much freedom in our architectures as possible.

---

An example with separate classes for datasource and delegate.

class TableViewDatasource: NSObject, UITableViewDataSource {
    // implement datasource
}

class TableViewDelegate : NSObject, UITableViewDelegate {
    // implement delegate
}

class ViewController: UIViewController {

     IBOutlet weak var tableView: UITableView! {
         didSet {
              tableView.dataSource = tableViewDatasource
              tableView.delegate = tableViewDelegate
         }
     }

     let tableViewDatasource = TableViewDatasource()
     let tableViewDelegate = TableViewDelegate()

}

This allows higher reusability and favours composition over inheritance, if you'd allow view controllers to hold different implementations of delegate and datasource.

You deal with smaller classes and those are easier to test and maintain.

It is even possible to design complete apps, that don't need any view controller subclasses.

---

datasource/delegate design can be as sophisticated as you like.

As an example I want to show you a new project of mine: TaCoPopulator. It is a framework to populate table view and collection views transparently by splitting it up in distinct task to follow the SOLID Principles:

import UIKit

class CollectionViewController: UIViewController {

    @IBOutlet weak var collectionView: UICollectionView!
    private var datasource: ViewControllerDataSource?

    override func viewDidLoad() {
        super.viewDidLoad()
        self.datasource = ViewControllerDataSource(with: collectionView)
    }
}

---

import UIKit

class TableViewController: UIViewController {

    @IBOutlet weak var tableView: UITableView!
    private var datasource: ViewControllerDataSource?

    override func viewDidLoad() {
        super.viewDidLoad()
        self.datasource = ViewControllerDataSource(with: tableView)
    }
}

---

import TaCoPopulator


class IntDataProvider: SectionDataProvider {

    override init(reuseIdentifer: @escaping (Int, IndexPath) -> String) {
        super.init(reuseIdentifer: reuseIdentifer)
        DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 2) {
            self.provideElements([1,2,3,4,5,6,7,8,9])
            DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 2) {
                self.provideElements(self.elements() + [10, 11, 12, 13, 14, 15])
            }
        }
    }
}

---

import TaCoPopulator


class ViewControllerDataSource {
    init(with populatorView: PopulatorView) {
        self.populatorView = populatorView
        setup()
    }

    var intSelected: ((Int, IndexPath) -> Void)?
    var stringSelected: ((String, IndexPath) -> Void)?

    let dp1 = IntDataProvider {
        _ in return "Cell"
    }

    let dp2 = StringDataProvider {
        _ in return "Cell"
    }


    weak var populatorView: PopulatorView?
    var populator: Populator?

    func setup(){
        dp1.selected = {
            [weak self] element, indexPath in
            self?.intSelected?(element, indexPath)
        }

        dp2.selected = {
            [weak self] element, indexPath in
            self?.stringSelected?(element, indexPath)
        }

        let collectionViewCellConfig: (Any, TextCollectionViewCell, IndexPath) -> TextCollectionViewCell  = {
            element, cell, _ in
            cell.textLabel?.text = "\(element)"
            return cell
        }

        let tableViewViewCellConfig: (Any, UITableViewCell, IndexPath) -> UITableViewCell  = {
            element, cell, _ in
            cell.textLabel?.text = "\(element)"
            return cell
        }

        if  let populatorView  = populatorView as? UICollectionView {
            let  section1factory = SectionCellsFactory(parentView: populatorView, provider: dp1, cellConfigurator: collectionViewCellConfig)
            let  section2factory = SectionCellsFactory(parentView: populatorView, provider: dp2, cellConfigurator: collectionViewCellConfig)
            self.populator = Populator(with: populatorView, sectionCellModelsFactories: [section1factory, section2factory])
        }

        if  let populatorView  = populatorView as? UITableView {
            let section1factory = SectionCellsFactory(parentView: populatorView, provider: dp1, cellConfigurator: tableViewViewCellConfig)
            let section2factory = SectionCellsFactory(parentView: populatorView, provider: dp2, cellConfigurator: tableViewViewCellConfig)
            self.populator = Populator(with: populatorView, sectionCellModelsFactories: [section1factory, section2factory])
        }
    }

}