Delegation to pass data back from modally presented view controller - ios

Question

Let's say we have two view controllers, a parent with a label and a modally presented child with a table view. How would I pass the user's selection in the table view back to the parent using delegation?
ViewController1:
var delegate: vc2delegate?
override func viewDidLoad {
super.viewDidLoad()
let label.text = ""
}
ViewController2:
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 5
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "Cell") as! Cell
let selections = ["1", "2", "3", "4", "5"]
cell.selections.text = selections[indexPath.row]
return cell
}
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
if let cell = tableView.cellForRow(at: indexPath) as? Cell {
cell.didSelect(indexPath: indexPath as NSIndexPath)
}
dismiss(animated: true, completion: nil)
}
//wherever end of class is
protocol vc2delegate {
// delegate functions here
}
Do I even have the right approach? I never really got down this pattern and I think it's crucial for me to learn for iOS. Another tricky caveat may be that viewDidLoad() doesn't get called when you dismiss a modal view controller.

Answer 1

Take a look at the UIViewController life cycle docs: ViewDidLoad only gets called once.
There are plenty of guides on how to do this, just do a quick search.
You'll need to update the dataSource logic as I added a quick string array, and you'll most likely have something a bit more complex, but the idea is still the same.
BTW, I used your naming convention of vc1/vc2, but I hope you have more meaningful names for your controllers.
In your code you have the delegate on the wrong VC. Here is a quick code sample of what it should look like:
class VC1: UIViewController {
let textLabel = UILabel()
// whenever you're presenting the vc2
func presentVC2() {
var vc2 = VC2()
vc2.delegate = self
self.present(vc2, animated: true, completion: nil)
}
}
extension VC1: VC2Delegate {
func updateLabel(withText text: String) {
self.textLabel.text = text
}
}
protocol VC2Delegate: class {
func updateLabel(withText text: String)
}
class VC2: UIViewController {
weak var delegate: VC2Delegate?
let dataSource = ["string 1", "tring 2"]
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
let string = dataSource[indexPath.row]
self.delegate?.updateLabel(withText: string)
dismiss(animated: true, completion: nil)
}
}

Answer 2

You can use callback function also to update your label from tableview:
1) Declare callback function into your VC2:
var callback:((String) -> Void)?
2) Call this function in your tableview CellForRowAt method in VC2:
let dataSource = ["string 1", "tring 2"]
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let string = dataSource[indexPath.row]
var cell = tableView.dequeueReusableCell(withIdentifier: "yourCell") as! YourCell
//here you can call callback function & pass string to VC1
cell.callback?(dataSource[indexPath.row])
}
3) Now you can call callback closure in VC1 in anywhere you call your VC2:
class VC1: UIViewController {
let textLabel = UILabel()
//I'm calling this(presentVC2()) function on ViewDidLoad you can call anywhere you want
func viewDidLoad() {
super.viewDidLoad()
presentVC2()
}
// whenever you're presenting the vc2
func presentVC2() {
var vc2 = VC2()
vc2.callback = { text in
self.textLabel.text = text
}
self.present(vc2, animated: true, completion: nil)
}
}