Swift IOS Issues updating Label in DetailView from MasterView - ios

Question

My first posting on stackoverflow, so sorry if its not right
I am using the Master/Detail View template in XCode. This is a BLT Central app and it gets notified of events happening on the BLE device.
I have a Master view, this is updated using
public func UpdateView() {
tableView.beginUpdates()
tableView.reloadRows(at: self.tableView.indexPathsForVisibleRows!, with: .none)
tableView.endUpdates()
}
This works fine and the TableView shows the updates live whenever the BLE notifies
However I also want to update the detail view live, incase this is being shown.
I have the label linked in the DetailView via:
#IBOutlet weak var detailDescription: UILabel!
And it updates just fine when the MasterView seques to the DetailView
However if I try to update the Label when the BLE notify arrives the #IBOutlet detailDescription has turned to nil, so the update fails (Label not linked)
func UpdateDetail() {
guard let label = detailDescription else {
return; //Label not linked
}
label.text = "New Data"
}
The UpdateDetail() function is also used in viewDidLoad() and in that case its working fine
Whats really weird is that if I add a timer in the DetailView to just do the update
var timer : Timer? = nil
#objc func fireTimer() {
DispatchQueue.main.async {
self.UpdateDetail()
}
}
It works fine, so its possibly something to do with calling the UpdateDetail() function from outside the Detail class.
I have checked if the detailDescription reference gets reset by adding a didSet to the property, and its only called once when the view is loaded
Guess I could use the timer work around, but I am totally baffled why the detailItem appears as nil sometimes, so would be grateful for a sanity check.
UPDATE Gone back to basics_______
So I have now gone back to the standard Apple Master->Detail view template and added a simple timer which updates the list. The ListView updates fine, however it still does not update the detail view dynamically. outside its own class.
I am using on a 1 second timer after MainView is loaded, the list view updates fine, however the detail does not.
When debugging it steps into configureView() fine, but detailDescriptionLabel is nil after the first viewDidLoad()
Have tried all the suggestions below, however in each case the weak reference to the label is nil after the initial Load
Totally baffled
#objc func doTimer() {
for index in 0..<objects.count {
objects[index]=(objects[index] as! NSDate).addingTimeInterval(1)
}
tableView.beginUpdates()
tableView.reloadRows(at: self.tableView.indexPathsForVisibleRows!, with: .none)
tableView.endUpdates()
DispatchQueue.main.async {
self.detailViewController?.configureView()
}
}
Full code for MasterViewController.swift here, rest is the same as standard template.
import UIKit
class MasterViewController: UITableViewController {
var detailViewController: DetailViewController? = nil
var objects = [Any]()
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
navigationItem.leftBarButtonItem = editButtonItem
let addButton = UIBarButtonItem(barButtonSystemItem: .add, target: self, action: #selector(insertNewObject(_:)))
navigationItem.rightBarButtonItem = addButton
if let split = splitViewController {
let controllers = split.viewControllers
detailViewController = (controllers[controllers.count-1] as! UINavigationController).topViewController as? DetailViewController
}
//Added timer here
_ = Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(doTimer), userInfo: nil, repeats: true)
}
//Update data in list
#objc func doTimer() {
for index in 0..<objects.count {
objects[index]=(objects[index] as! NSDate).addingTimeInterval(1)
}
tableView.beginUpdates()
tableView.reloadRows(at: self.tableView.indexPathsForVisibleRows!, with: .none)
tableView.endUpdates()
DispatchQueue.main.async {
self.detailViewController?.configureView()
}
}
override func viewWillAppear(_ animated: Bool) {
clearsSelectionOnViewWillAppear = splitViewController!.isCollapsed
super.viewWillAppear(animated)
}
#objc
func insertNewObject(_ sender: Any) {
objects.insert(NSDate(), at: 0)
let indexPath = IndexPath(row: 0, section: 0)
tableView.insertRows(at: [indexPath], with: .automatic)
}
// MARK: - Segues
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "showDetail" {
if let indexPath = tableView.indexPathForSelectedRow {
let object = objects[indexPath.row] as! NSDate
let controller = (segue.destination as! UINavigationController).topViewController as! DetailViewController
controller.detailItem = object
controller.navigationItem.leftBarButtonItem = splitViewController?.displayModeButtonItem
controller.navigationItem.leftItemsSupplementBackButton = true
}
}
}
// MARK: - Table View
override func numberOfSections(in tableView: UITableView) -> Int {
return 1
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return objects.count
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)
let object = objects[indexPath.row] as! NSDate
cell.textLabel!.text = object.description
return cell
}
override func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
// Return false if you do not want the specified item to be editable.
return true
}
override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {
if editingStyle == .delete {
objects.remove(at: indexPath.row)
tableView.deleteRows(at: [indexPath], with: .fade)
} else if editingStyle == .insert {
// Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view.
}
}
}

Answer 1

My answer is based on the provided Git repository.
In MasterViewController - you are calling self.detailViewController?.configureView() but you never assign the detail controller and because it's nil it fails to call the configureView function. You can do that in prepare(for segue: UIStoryboardSegue, sender: Any?) by setting self.detailViewController = controller
This won't still help you with the update of the label value.
The reason fo that is because in #objc func doTimer() { you are always setting (overriding) a new Date object into your array (what you probably aimed for is to update value for same reference). Because of this, the reference you assigned to detailViewController is different and you never update the detailItem in your timer. Hence calling the configureView won't make any change as the value remained the same.

Answer 2

It's happening because your detailDescription label is weak "weak var detailDescription". and each time you write this code
guard let label = detailDescription else {
return; //Label not linked
}
label.text = "New Data"
you create a new object and assign value to that object. So the original value for detailDescription label object doesn't change. Try using the same detailDescription object everytime when you change its value.