Pass variables from one ViewController to another in Swift
I have a calculator class, a first ViewController to insert the values and a second ViewController to show the result of the calculation. Unfortunately I get a error called "Can't unwrap Optional.None" if I click the button. I know it's something wrong with the syntax, but I don't know how to improve it.
The button in the first Viewcontroller is set to "Segue: Show (e.g. Push)" in the storyboard to switch to the secondViewController if he gets tapped.
the calculator class is something like:
class Calculator: NSObject {
func calculate (a:Int,b:Int) -> (Int) {
var result = a * b
return (result)
}
}
The Viewcontroller calls the function, inserts a/b and wants to change the label which is located in the secondviewcontroller:
class ViewController: UIViewController {
@IBAction func myButtonPressed(sender : AnyObject) {
showResult()
}
var numberOne = 4
var numberTwo = 7
var myCalc = Calculator()
func showResult () {
var myResult = myCalc.calculate(numberOne, b: numberTwo)
println("myResult is \(String(myResult))")
var myVC = secondViewController()
myVC.setResultLabel(myResult)
}
And here is the code of the secondViewController
class secondViewController: UIViewController {
@IBOutlet var myResultLabel : UILabel = nil
func setResultLabel (resultValue:Int) {
myResultLabel.text = String(resultValue)
}
init(coder aDecoder: NSCoder!)
{
super.init(coder: aDecoder)
}
Solution 1:
In Swift, everything is public by default. Define your variables outside the classes:
import UIKit
var placesArray: NSMutableArray!
class FirstViewController: UIViewController {
//
..
//
}
and then access it
import UIKit
class TableViewController: UITableViewController {
//
placesArray = [1, 2, 3]
//
}
Solution 2:
The problem here is that the FirstViewController
has no reference to the instance of SecondViewController
. Because of this, this line:
secondViewController.setResultLabel(myResult)
does nothing (except probably causing the Can't unwrap Optional.None
error). There are a few ways to solve this problem. If you are using storyboard segues you can use the -prepareForSegue
method of UIViewController
. Here is an example:
In FirstViewController:
override func prepareForSegue(segue: UIStoryboardSegue!,sender: AnyObject!){
//make sure that the segue is going to secondViewController
if segue.destinationViewController is secondViewController{
// now set a var that points to that new viewcontroller so you can call the method correctly
let nextController = (segue.destinationViewController as! secondViewController)
nextController.setResultLabel((String(myResult)))
}
}
Note: this code will not run as is because the function has no access to the result variable. you'll have to figure that out yourself :)