How do you pass data between view controllers in Swift? - ios

Question

I tried creating global variables and updating the information when the view is loaded but data isn't being rendered.
GLOBAL VARIABLES
var viewName:String = ""
var viewDuration:String = ""
var viewPeriod:String = ""
var viewMinAmp:String = ""
var viewMaxAmp:String = ""
var viewStep:String = ""
var viewType:String = ""
Is there a more efficient way of passing information other than having global variables?
#IBOutlet var txtName: UITextField!
#IBOutlet var txtDuration: UITextField!
#IBOutlet var txtPeriod: UITextField!
#IBOutlet var txtMinAmp: UITextField!
#IBOutlet var txtMaxAmp: UITextField!
#IBOutlet var txtStep: UITextField!
#IBOutlet var txtType: UITextField!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
setInfo(viewName, duration: viewDuration, period: viewPeriod, minAmp: viewMinAmp, maxAmp: viewMaxAmp, step: viewStep, type: viewType)
}
func setInfo(name: String, duration: String, period: String, minAmp: String, maxAmp: String, step: String, type: String) {
txtName.text = name
txtDuration.text = duration
txtPeriod.text = period
txtMinAmp.text = minAmp
txtMaxAmp.text = maxAmp
txtStep.text = step
txtType.text = type
}

Answer 1

One solution would be to override prepareForSegue(segue:sender:) from within the view controller which contains the data that you wish to pass to the destination view controller.
override func prepareForSegue(segue: UIStoryboardSegue!, sender: AnyObject!) {
if (segue.identifier == "YourSegueName") {
//get a reference to the destination view controller
let destinationVC:ViewControllerClass = segue.destinationViewController as! ViewControllerClass
//set properties on the destination view controller
destinationVC.name = viewName
//etc...
}
}

Answer 2

For Swift 3.0
final class Shared {
static let shared = Shared() //lazy init, and it only runs once
var stringValue : String!
var boolValue : Bool!
}
To set stringValue
Shared.shared.stringValue = "Hi there"
to get stringValue
if let value = Shared.shared.stringValue {
print(value)
}
For Swift version below 3.0
You can pass data between views using singleton class. It is easy and efficient way. Here is my class ShareData.swift
import Foundation
class ShareData {
class var sharedInstance: ShareData {
struct Static {
static var instance: ShareData?
static var token: dispatch_once_t = 0
}
dispatch_once(&Static.token) {
Static.instance = ShareData()
}
return Static.instance!
}
var someString : String! //Some String
var selectedTheme : AnyObject! //Some Object
var someBoolValue : Bool!
}
Now in my ViewControllerOne I can set above variable.
//Declare Class Variable
let shareData = ShareData.sharedInstance
override func viewDidLoad() {
self.shareData.someString ="Some String Value"
}
And in my ViewControllerTwo I can access someString as
let shareData = ShareData.sharedInstance
override func viewDidLoad() {
NSLog(self.sharedData.someString) // It will print Some String Value
}

Answer 3

Personally, I prefer ways as follow:
If you want to jump forward between two view controllers (from A to B), as -pushViewController:animated: in navigation, you can define a property of model for Controller B and expose it publicly, then set this property explicitly before jumping from Controller A, it's pretty straightforward;
In case you want to jump backward from Controller B to A, use Delegate+Protocol mode. Controller B drafts a public protocol and own a "delegate" property, any object who would like to be the delegate of Controller B shall comply and implement its protocol(optionally). then prior to the jumping-backward, Controller B makes its delegate perform certain action(s) listed in protocol, the data could be transferred in this way;
Under certain circumstance, you may want to transfer data from a Controller(or controllers) to other multiple Controllers, use Notification mechanism if this is the case.
Apple has detailed instructions about delegate mode, notification mode in official documentation, check them out in XCode, :)

Answer 4

Just need to follow 3 steps, let's assume you want to pass data from ViewControllerA to ViewControllerB:
create a segue between ViewControllerA and ViewControllerB
name the segue with a Identifier in the attributes inspector of it
override the prepareForSegue(segue: UIStoryboardSegue!, sender: AnyObject!) at ViewControllerA
For step#3,:
if you are not using swift 2.1, please follow #Scott Mielcarski 's answer at this question
for people who are using swift 2.1, or who get error "Cannot convert value of type 'UIViewController' to specified type 'your view Controller class name', After following #Scott Mielcarski 's answer at this question, Please use:let destinationVC:ViewControllerClass = segue.destinationViewController as! ViewControllerClass instead of
let destinationVC:ViewControllerClass = segue.destinationViewController
This is tested on Swift 2.1.1 and it works for me.

Answer 5

If you don't actually want to pass data between view controllers but rather simply want to store a global variable you can do this:
This gives a great explanation for how to do this in Swift 5: https://www.hackingwithswift.com/example-code/system/how-to-save-user-settings-using-userdefaults
Summary:
To set a value:
let defaults = UserDefaults.standard
defaults.set("value", forKey: "key")
To get a String value:
let key = defaults.object(forKey: "StringKey") as? [String] ?? [String]()
To get integer value:
let key = defaults.integer(forKey: "IntegerKey")