I am new to xcode 7 and it would be great if you could help me with something.
I have two ViewControllers and I would like to call ViewController2 from ViewController1. I need to do that by code. (I would like to call it from the viewDidLoad()-function)
Thanks in advance
Depending on how you have the project and your navigation setup, here is one of the many ways to accomplish what I think you are asking.
If you are using Segues for navigation, in the ViewController1 (That initialized the navigation) you would override the prepareForSegue function cast your segue.destination as ViewController2 and set the property. Like this
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
super.prepare(for: segue, sender: sender)
guard let viewController2 = segue.destination as? ViewController2 else { return }
viewController2.propertyName = "Property Value"
}
Or, if you are wanting to instantiate ViewController2 in ViewController1 you could do this:
override viewDidLoad() {
super.viewDidLoad()
guard let viewController2 = self.storyboard?.instantiateViewController(withIdentifier: "ID for ViewController (set in the Storyboard)") as? ViewController2 else { return }
viewController2.propertyName = "Property Value"
self.present(viewController2, animated: true, completion: nil)
// Or you could do if you want a full navigation, not just a modal.
self.show(viewController2, sender: self)
}
If you are wanting to access each view controller, you could do something like this:
class ViewController2: UIViewController {
weak var viewController1: ViewController1? //The 'weak' keyword is incredibly important so that you don't have a memory leak.
override viewDidLoad() {
self.viewController1.propertyName = "Property Value"
}
}
Using the same steps as above, you can set the viewController1 property in the ViewController2 instance.
Now I hope that answers your question. Your question is a little vague, so I am shooting in the dark.
Related
I want to pass data from ViewController1 to ViewController2. ViewController2 is embedded within a Navigation Controller (because I have a Segmented Control that corresponds to 3 Child View Controllers). My segue is directly from ViewController1 to the Navigation Controller.
I tried the following in ViewController1:
ViewController2().testID = "test value"
With the following in ViewController2:
var testID = ""
However testID does not update when I run print(testID) in ViewController2.
What is recommended for passing data from ViewController1 to ViewController2? Any help/advice is much appreciated!
You can pass the value by overriding the prepare(for segue:) function in ViewController1
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
// Get the new view controller using segue.destination
guard let destination = segue.destination as? UINavigationController else {
return
}
guard let finalDestination = destination.viewControllers.first as? ViewController2 else {
return
}
finalDestination.testID = "Test Value"
}
NSUserDefaults will always work.
I've set up a simple Swift project to try and wrap my head around delegates & protocols. The goal is to pass data between two classes (SendingClass & ReceivingClass). Two buttons in the SendingClass are linked to the delegate which should trigger the Protocol conforming function in the ReceivingClass to execute. This doesn't work unfortunately, I suspect it has to do with where and how I am declaring the ReceivingClass as the delegate.
Appreciate your insights, i'm just starting out!
I've tried setting the delegate in various locations (presently within viewDidLoad, but cant get it to work).
let vc = SendingClass()
vc.statusDelegate = self
SendingClass.swift
import UIKit
protocol StatusDelegate {
func statusChanged(state: Bool, sender: String)
}
class SendingClass: UIViewController {
var statusDelegate : StatusDelegate?
#IBAction func button1Pressed(_ sender: UIButton) {
statusDelegate?.statusChanged(state: true, sender: "Button 1")
}
#IBAction func button2Pressed(_ sender: UIButton) {
statusDelegate?.statusChanged(state: false, sender: "Button 2")
}
}
ReceivingClass.swift
import Foundation
import UIKit
class ReceivingClass: UIViewController, StatusDelegate {
override func viewDidLoad() {
let vc = SendingClass()
vc.statusDelegate = self
}
func statusChanged(state: Bool, sender: String) {
print("Sender = \(sender) , State = \(state)")
}
}
Expected: the ReceivingClass protocol conforming function (func statusChanged) should execute each time the buttons are pressed within the SendingClass.
Actual: Nothing happens
I am using this..
// create extension in your receiving class
extension ReceivingClass: PopUpVCDelegate {
func statusChanged(state: Bool, sender: String) {
print("Sender = \(sender) , State = \(state)")
}
}
// on sending class, when you present your receiving class on any button click
eg.
let resultController = self.storyboard?.instantiateViewController(withIdentifier: "PopUpVCID") as? PopUpVC
resultController?.delegate = self
self.present(resultController!, animated: true, completion: nil)
//or if not have button add on viewdidload in receiving class
// here is full eg
How to get data from popup view controller to custom table view cell?
For protocol and delegate, you use it when u want to bring a value from 2nd VC (presented by 1st or pushed by 1st VC) to 1st VC, which is the original.
From your code, I dont see you presenting or pushing your 2nd VC. that's why it's not working. Hopefully I answered your doubt.
However if you still want to bring a value over from 1st VC to 2nd VC. In second VC, create a variable to receive it
var ReceivedData = String()
then from your first VC, when u are going to push it,
let vc = SendingClass()
vc.ReceivedData = "Whatever you want it to receive"
If you're using storyboard segues, maybe the view controller is instantiated from there so probably you have to use the prepareForSegue and get the destination view controller (which is already instantiated for you) in the ReceivingClass view controller:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
super.prepare(for: segue, sender: sender)
if let destination = segue.destination as? SendingClass {
destination.delegate = self
}
}
Also be careful with delegate patter: the delegate property should be declared as a weak property to avoid retain-cycle
weak var delegate: MyDelegate?
Trying to pass data from one view controller MainScreenVC to Another RatesVC with protocol and extension, but that's not working, app crashing everytime . I'm clearly see that problem with code on second VC(because print showing correct data after action on first VC) but not sure where is error.
StoryBoard and 1st VC Example
Second VC
1st View controller
import UIKit
protocol transferNameOfCurrency {
func currencySelected(nameOfCurrency: String)
}
class MainScreenVC: UIViewController {
var transferCurrencyDelegate: transferNameOfCurrency?
var nameOfTheCurrency: String?
#IBAction func updateRates(_ sender: Any) {
nameOfTheCurrency = "EUR"
transferCurrencyDelegate?.currencySelected(nameOfCurrency:
nameOfTheCurrency)
print(nameOfTheCurrency)
}
}
2nd ViewController
import UIKit
class RatesVC: UIViewController {
var currencySelected: String?
override func viewDidLoad() {
super.viewDidLoad()
if let push = self.storyboard?.instantiateViewController(withIdentifier: "MainScreenVC") as? MainScreenVC
{
push.transferCurrencyDelegate = self
}
// Do any additional setup after loading the view.
}
}
extension RatesVC: transferNameOfCurrency {
func currencySelected(nameOfCurrency: String) {
currencySelected = nameOfCurrency
print(currencySelected)
}
}
The most obvious problem lies here:
if let push = self.storyboard?.instantiateViewController(withIdentifier: "MainScreenVC") as? MainScreenVC {
push.transferCurrencyDelegate = self
}
You have to realize that instantiateViewController creates a new view controller - it's not the reference to the view controller presented at the screen. In that code you just created a completely new view controller and then set its delegate to self, but otherwise nothing else.
Without knowing the context it is really hard to suggest anything - prepare(for:) segue might be the place where you want to set the delegate. Anyway, the problem is that you have to obtain a reference to the controller that is presented on the screen, the one that is supposed to be reacting to those events.
Moreover, from the memory management aspect, you should really consider making the delegate property a weak one to prevent memory leaks.
EDIT
So after seeing the minimal working example you provided at link, I think I can provide the solution on how to get that string to the SecondVC.
Your first view controller with comments:
import UIKit
class ViewController: UIViewController {
var newLine: String = "EUR"
#IBAction func push(_ sender: Any) {
// here the secondVC does not exist yet, calling delegate.transferWord() here would have no sense
// performSegue will create that secondVC, but now it does not exist, nor it is set up as the delegate
self.performSegue(withIdentifier: "ViewController", sender: navigationController)
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if let secondVC = segue.destination as? SecondVC, segue.identifier == "ViewController" {
// at this moment secondVC did not load its view yet, trying to access it would cause crash
// because transferWord tries to set label.text directly, we need to make sure that label
// is already set (for experiment you can try comment out next line)
secondVC.loadViewIfNeeded()
// but here secondVC exist, so lets call transferWord on it
secondVC.transferWord(word: newLine)
}
}
}
No need for delegates here, because your ViewController is the one pushing the SecondVC to the Navigation controller - that means that you can access it directly in prepare(for:), as you can see above.
Now the SecondVC is super simple (I omitted unnecessary code):
import UIKit
class SecondVC: UIViewController {
#IBOutlet weak var label: UILabel!
func transferWord(word: String) {
label.text = word
}
}
Storyboards can stay as they are.
I know this is Duplicate Question, but i didn't find the solution for my problem. I have two controllers. HomeViewcontroller's variable of "myValue"'s value can't be set by using ViewController class.I don't know the issue here but code is working without error.But when i print "myValue" it shows nil.Destination view controller is not the controller that i want to set variable value. Destination view controller is a tab bar controller, so i want to set the variable value of first tab bar and second tab bar view controllers. This is my code :-
import UIKit
class ViewController: UIViewController {
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject!) {
if(segue.identifier == "gotoHome") {
println("1111")
var storyboard = UIStoryboard(name: "Main", bundle: nil)
var viewController = storyboard.instantiateViewControllerWithIdentifier("HomeViewController") as! HomeViewController
viewController.myValue = 8888
}
}
}
this is the other view controller
import UIKit
class HomeViewController: UIViewController {
var myValue: Int!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
println(myValue)
}
}
You don't need to instantiate the viewcontroller, as it is already been done, you just need to fetch the viewcontroller for the current segue operation, so your code should look like below
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject!) {
if(segue.identifier == "gotoHome") {
println("1111")
let controller = segue.destinationViewController as! UITabBarController
let homeController = controller.selectedViewController as !HomeViewController
homeController.myValue = 8888
}
}
Hope it helps.
Change to :
let viewController = segue.destinationViewController as! HomeViewController
You're printing the value of myValue in viewDidLoad which is called when you're instantiating it from your storyboard. You're setting myValue after creating your instance. Try to print myValue in viewWillAppear for example, then it should be set.
This is a totally dumb question I am sure. I have a viewcontroller that is inside a navigation controller that is inside a TabBarController. Apple says this is the right way to implement that setup. However, how can I prepareForSeque to that complex and send data to the first ViewController.
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if segue.identifier == "presentActionItems" {
println("preparing")
let tabBarController:actionItemsTabController = segue.destinationViewController as! actionItemsTabController
let navigationController = ???
let viewController = ???
viewController.givenURL = actionItemsURL
}
}
I am sure this is an easy question, can I have some help.
Try this in your TabController's viewDidLoad after passing it your data
let firstViewController : UIViewController = self.viewControllers.objectAtIndex(0).topViewController;
firstViewController.this = self.this;
firstViewController.that = self.that;