How to access a referencing outlet from a different view controller? - swift

Question

I am new to Swift and Xcode. I am building an Financial Expense ios app.
In my first view controller, I created a referencing outlet for a label called expenseNum.
In my second view controller, I have a function for a button called Add Expense. When it is clicked, I need it to update the expenseNum variable with the amount of the expense.
What is the best way to go about this? I had created an object of the first view controller class and accessed it like "firstviewcontroller.expenseNum" but this will create a new instance of the class and I need it to be all the same instance so it can continuously add to the same variable. Thanks for the help!

Answer 1

You need a delegate
protocol SendManager {
func send(str:String)
}
In first
class FirstVc:UIViewcontroller , SendManager {
func send(str:string) {
self.expenseNum.text = str
}
}
when you present SecondVc
let sec = SecondVc()
sec.delegate = self
// present
In second
class SecondVc:UIViewcontroller {
var delegate:SendManager?
#IBAction func btnClicked(_ sender:UIButton) {
delegate?.send(str:"value")
}
}
// setting delegate
in viewDidLoad of SecondVc
if let first = self.tabBarController.viewControllers[0] as? FirstVc {
self.delegate = first
}

Answer 2

There are several ways you can pass data from ViewController2 to another ViewController1
The best way here is Protocol Delegates
Please follow below steps to pass data
In Your SecondViewController from where you want to send data back declare a protocol at the top of class declaration
protocol SendDataBack: class {
func sendDataFromSecondVCtoFirstVC(myValue: String)
}
Now in the class , declare a object of your protocol in same ViewController
weak var myDelegateObj: SendDataBack?
And now in your Add Expense button action just call the delegate method
myDelegateObj?.sendDataFromSecondVCtoFirstVC(myValue: yourValue)
Now go to your first ViewController
the place from where you have pushed/present to SecondViewController you must have taken the object of SecondVC to push to push from first
if let secondVC = (UIStoryboard.init(name: "Main", bundle: nil)).instantiateViewController(withIdentifier: "secondVCID") as? SecondViewController {
vc?.myDelegateObj = self
self.navigationController?.pushViewController(secondVC, animated: true)
**OR**
self.present(secondVC, animated: true, completion: nil)
}
now in your FirstViewController make an extension of FirstViewVC
extension FirstViewController: SendDataBack {
func sendDataFromSecondVCtoFirstVC(myValue: String) {
}
}

Answer 3

I think you can make a variable in your properties in second ViewController (before viewDidLoad method)
var delegate: FirstViewController? = nil
and use from the properties of the first view controller anywhere of the second view controller.
delegate!.mainTableView.alpha=1.0
//for example access to a tableView in first view controller

Answer 4

The simplest way to achieve this is to use a public var. Add a new Swift file to your project, call it Globals. Declare the public variable in Globals.swift like so:
public var theValue: Int = 0
Set its required value in the first ViewController, and you'll find you can read it in the second with ease.