Unable to share data between tab view controllers? - swift

Question

I am making an app where I take in user input and display it as a chart, which requires an array of data. I have managed to save data in an array using core data and I cannot figure out how to share that data from one tab to the other TabViewController.
here is how the data is stored and fetched in the FirstViewController
let number = Numbers(context: PersistenceService.context)
number.numberInArray = Int16(numberEnteredInSlider)
PersistenceService.saveContext()
testArray.append(Int(Double(number.numberInArray)))
var numbers = [Numbers]() // Where Numbers = NSManaged Class
var fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Numbers")
do {try numbers = PersistenceService.context.fetch(fetchRequest) as! [Numbers]
for number in numbers {
print(number.numberInArray)
}
}catch {
print("error")
}
and here is the output(printed testarray):
SAVED
2
5
6
5
Now I want to share this test array from one view controller to another(chartsViewController)
this is what I have tried
class chartsViewController: UIViewController {
let mainVC = mainViewController(nibName: "mainViewController", bundle: nil)
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
print(mainVC.testArray)
updateGraph()
func updateGraph() {
var lineChartEntry = [ChartDataEntry]() //this is the Array that will eventually be displayed on the graph.
for i in 0..<mainVC.testArray.count {
//
let value = ChartDataEntry(x: Double(i), y: Double(mainVC.testArray[i]))
// here we set the X and Y status in a data chart entry
lineChartEntry.append(value)
// here we add it to the data set
}}
//only showing the part needed. I have tried the same solution with another array and it worked.
}
and the output comes as [0]
I have also tried making a singleton but that didn't work out.

Answer 1

To pass data between tabs on UITabBarController /tabBar, what needs to be done is to have an intermediate. (This is usually the main UITabBarController)
Pic of UITabBarController and the child tabbar
Create a Class and link it to this TabBarController within IB
class BaseTBController: UITabBarController {
// Provide the variable which we want to pass
var workoutTitle: String = "Select a Workout"
override func viewDidLoad() {
super.viewDidLoad()
}
}
Assuming you want to pass data from TabBar2 to TabBar1, then on TabBar2 (in this case, I have it as a UITableView). In the delegate method:
extension VCLibrary: UITableViewDelegate{
// method to run when table view cell is tapped
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
// prepare to store the data to be passed to another TabBar
let tabbar = tabBarController as! BaseTBController
tabbar.workoutTitle = jsonErgWorkouts[indexPath.row].title
// Automatically select Tab1 after choosing
self.tabBarController?.selectedIndex = 0
// Deselect the selected row once we move to Tab1
tableView.deselectRow(at: indexPath, animated: true)
}
}
After selecting the data to be passed, the code (above) will automatically switch to Tab1. Within Tab1, the following code is aimed to receive the passed data
override func viewDidAppear(_ animated: Bool) {
// Obtain Passed in values from BaseTBController
let tabbar = tabBarController as! BaseTBController
// populate the Title as passed from Tab2
workoutTitleLabel.text = tabbar.workoutTitle
}
I learned this from:
https://www.youtube.com/watch?v=GL8-eM93EvQ