Swift - UITableView doesn't work with delegates - ios

Question

The problem is that UITableView.dataSource works fine with extensions, but does not work with delegates.
I created new project and added just one UITableView to the storyboard.
Here is the code using extension:
import UIKit
class ViewController: UIViewController {
#IBOutlet weak var tableView: UITableView!
override func viewDidLoad() {
super.viewDidLoad()
tableView.dataSource = self
// tableView.dataSource = Delegate()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
}
extension ViewController: UITableViewDataSource {
//class Delegate: NSObject, UITableViewDataSource {
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
print(1) // called several times
return 1
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
print(2) // called
var cell = tableView.dequeueReusableCell(withIdentifier: "UITableViewCell")
if cell == nil {
cell = UITableViewCell(style: .default, reuseIdentifier: "UITableViewCell")
}
return cell!
}
}
Using delegate:
import UIKit
class ViewController: UIViewController {
#IBOutlet weak var tableView: UITableView!
override func viewDidLoad() {
super.viewDidLoad()
// tableView.dataSource = self
tableView.dataSource = Delegate()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
}
//extension ViewController: UITableViewDataSource {
class Delegate: NSObject, UITableViewDataSource {
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
print(1) // called several times
return 1
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
print(2) // doesn't called
var cell = tableView.dequeueReusableCell(withIdentifier: "UITableViewCell")
if cell == nil {
cell = UITableViewCell(style: .default, reuseIdentifier: "UITableViewCell")
}
return cell!
}
}
Has anyone encountered such a problem?

Answer 1

You need to store your Delegate object in you view controller. The reason for this is that dataSource variable of UITableView is a weak variable (so as to prevent retain cycles) - it means that if it isn't stored somewhere in a strong variable, it will immediately get deallocated.
tableView.dataSource = Delegate()
Here you assign new instance of Delegate to a weak variable and nowhere else. Do something like this
class ViewController: UIViewController {
var delegate = Delegate()
override func viewDidLoad() {
super.viewDidLoad()
tableView.dataSource = self.delegate
}

Answer 2

The dataSource and delegate are both weak. So your Delegate() object with no strong reference will be released after viewDidLoad().
If you want to use delegate this way, just var delegate: Delegate! in your ViewController. Then in the viewDidLoad() :
self.delegate = Delegate()
tableView.delegate = self.delegate