UITableView not refreshing after dismissing ViewController above - ios

Question

I have a ViewController being presented using Apple's new default ModalTransitionStyle. And when that ViewController is dismissed, the ViewController below (that has a TableView) doesn't update the table.
I have tried ViewWill/DidAppear but in both cases, I get the error "Unexpectedly found nil while unwrapping an optional Value" when trying to access the table.
I have checked what methods get called and I found that numberOfRowsInSection gets called and cellForRowAtIndexPath doesn't get called. The table is for sure visible. It is not height 0 and numberOfRowsInSection doesn't get 0 returned.
I made a quick test project to demonstrate what I mean.
Image when App Runs
When Popup button clicked
When i go back
import UIKit
var cells = 5
class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
#IBOutlet weak var table: UITableView!
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return cells
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "test")
return cell!
}
override func viewDidLoad() {
super.viewDidLoad()
table.reloadData()
// Do any additional setup after loading the view.
}
#IBAction func popup(_ sender: Any) {
performSegue(withIdentifier: "popover", sender: self)
}
}
import UIKit
class PopoverViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
cells += 1
// Do any additional setup after loading the view.
}
#IBAction func back(_ sender: Any) {
let vc = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(identifier: "vc") as! ViewController
self.dismiss(animated: true)
}
}
What should happen is that everytime i go back to the view 1 more cell is being displayed. I checked if the count "Cell" is being increased and it is. I just cant figure out how to reload the table.

Answer 1

Old answer:
DispatchQueue.main.async { [weak self] in
self?.table.reloadData()
}
New Answer:
One of the your mistakes is that
let vc = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(identifier: "vc") as! ViewController
self.dismiss(animated: true, completion: {
vc.table.reloadData()
})
The vc is not your living Main Controller, you've to send living controller's reference.
By the way.
class PopoverViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
cells += 1
// Do any additional setup after loading the view.
}
#IBAction func back(_ sender: Any) {
let vc = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(identifier: "vc") as! ViewController
self.dismiss(animated: true, completion: {
vc.table.reloadData()
})
}
}
And your viewDidLoad method should be like:
override func viewDidLoad() {
super.viewDidLoad()
//table.reloadData()
// Do any additional setup after loading the view.
view.addSubview(table)
table.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
table.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
table.heightAnchor.constraint(equalTo: view.heightAnchor).isActive = true
table.widthAnchor.constraint(equalTo: view.widthAnchor).isActive = true
NotificationCenter.default.addObserver(self,
selector: #selector(notify),
name: .notifier,
object: nil)
self.navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: UIBarButtonItem.SystemItem.action,
target: self,
action: #selector(hh))
}
hh function is just for programmatically present Popover
#objc private func notify(notification: NSNotification){
//do stuff using the userInfo property of the notification object
print("notification has called")
DispatchQueue.main.async {
self.table.reloadData()
}
}
extension Notification.Name {
static let notifier = Notification.Name("notifier")
}
And change your cells variable like this:
var cells = 5{
didSet{
NotificationCenter.default.post(name: .notifier, object: nil)
}
}
I've created a Notification pattern to messaging between pages. It worked for me. When you increase cells instance Notification has notified and cell's has updated.

Answer 2

As i understand ViewController is parent, PopoverViewController is child. After child is dismissed, parent should update tableview.
viewDidLoad is called once for parent, it wont be called for dismissal of child.
So, you may define any delegate or closure for child view controller, which reload tableview at parent. you can call it at completion of dismiss.
dismiss(animated: Bool, completion: (() -> Void)?)
class PopoverViewController: UIViewController {
var onDismiss: (() -> Void)?
//...
}
// Also add this method to viewcontroller
class ViewController: UIViewController {
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier = "popover" {
guard let popoverVC = segue.destination as? PopoverViewController else {
return
}
popoverVC.onDismiss = { [unowned self] in
self.tableView.reloadData()
}
}
}
Also you don't need to create parent for dismissal.
let vc = UIStoryboard(name: "Main".. this line is unnecessary. this new vc is not shown so if you try to reach it, crash will occur due to outlets' nil value.