How to call a function from another controller in swift - swift

Question

I set the Show Charts button on the DetailView Controller which triggers the getChartData function and shows me the values in display view in charts, now I want to call that function in the didselectrow on the main Viewcontroller so that the chart is loaded automatically, but it fails.
When I tried to call that function in didselectrow (DVC.getChartsData) I got the error "Thread 1: Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value"
DVC.getChartsData
Thread 1: Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value
ViewController:
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
let Storyboard = UIStoryboard(name: "Main", bundle: nil)
let DVC = Storyboard.instantiateViewController(withIdentifier: "DetailViewController") as! DetailViewController
DVC.getDetailName = coin[indexPath.row].name
let formatedRoundingPrice = (coin[indexPath.row].price as NSString).floatValue * currencymodel.indexValue
let formatedPrice = String (format: "%.3f", formatedRoundingPrice)
DVC.getDetailPrice = formatedPrice
self.navigationController?.pushViewController(DVC, animated: true)
let percentage = String ((coin[indexPath.row].percent as NSString).floatValue)
DVC.getDetailPercent = percentage
tableView.deselectRow(at: indexPath, animated: true)
//DVC.getChartData()
}
DetailViewController:
#IBAction func tapLineChart(_ sender: Any) {
getChartData()
}
func getChartData () {
let chart = HITLineChartView(frame: CGRect(x: 0, y: 0, width: UIScreen.main.bounds.width, height: displayView.bounds.height))
displayView.addSubview(chart)
let max = String((priceResult.max() ?? 0.0).rounded(.up))
let min = String((priceResult.min() ?? 0.0).rounded(.down))
let maxChange = abs((listOfChanges.max()) ?? 0.0).rounded(.up)
let minChange = abs((listOfChanges.min()) ?? 0.0).rounded(.up)
absMaxPercentage = Int(maxChange > minChange ? maxChange : minChange)
titles = ["\(getDetailName) closing price is \(getDetailPrice)"]
print(data)
chart.draw(absMaxPercentage,
values: listOfChanges,
label: (max: max, center: "", min: min),
dates: namesArray,
titles: titles)
addCloseEvent(chart)
finalURL = baseURL + "bitcoin" + "/market_chart?vs_currency=usd&days=5"
print(finalURL)
getBitcoinData(url: finalURL)
}
How to load my charts tap on a specific tableview cell instead of tapping on tapLineChart.
https://imgur.com/fg2502P
https://imgur.com/C4AzaRY
https://imgur.com/jOrwujy

Answer 1

if you want to call a function on viewControllerB that you declare from viewController A.
just create the object of the class file you want to use the function from
var obj mainVC = MainViewController()
class MainViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
}
func commonMethod() {
print("From the main class")
}
}
Using that object, call the function in another file where you mean to use it
class OtherViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
mainVC.commonMethod()
// Do any additional setup after loading the view, typically from a nib.
}
}
Additionally, You can also create a new swift file, name it Global.swift, create all your functions that you want to use throughout the application here. They become "global functions"

Answer 2

You will want to use delegates or observers to pass data between view controllers.
I'm new to tutorials, but I wrote a bit about this here: https://www.eankrenzin.com/swift-blog/pass-data-throughout-your-app-with-observers-and-notifications-xcode-11-amp-swift-5
You should use optional binding to unwrap your VC let DVC = Storyboard.instantiateViewController(withIdentifier: "DetailViewController") as! DetailViewController
Your code is crashing because of that line. Check your interface builder to make sure the identifier is correct. Edit: this line was not causing a crash, but it is still better to use optional binding.The line is: https://imgur.com/CVP1x6H
NOTE: It is terrible practice to litter your app with instances when delegates and observers could work. Also do NOT have globals. Globals are disastrous for debugging and create tech debt.