I am re-writing a tutorial converting the code from Objective-C to swift. The app moves from VC one where there is 3 sliders (Red, Green and Blue) that set the background colour, a label of the colour name and a button that links to the second VC. In the second VC the colour from the first VC is used as the background and the user has a chance to name the colour.
When the user enters the colour name it should return the new colour name to the orginal VC and the label that shows the colour name should show the text entered.
The following is the code that is causing issue:
func textFieldShouldReturn(nameEntry: UITextField) -> Bool
{
ViewController().colourLabel.text = nameEntry.text
nameEntry.resignFirstResponder()
dismissViewControllerAnimated(true, completion: nil)
return true
}
The error "fatal error: unexpectedly found nil while unwrapping an Optional value" is generated. However debugging nameEntry.text has a string in it.
I'm a little stumped. I could try and do a prepare for unwind segue but it is meant to be a tutorial app.
Cheers
ViewController() actually creates a new instance of your ViewController. This is not a reference to the already existing ViewController. What you can do is create a weak variable pointing to first ViewController inside the second ViewController and set it at prepareForSegue or when the second View controller is shown.
class SecondViewController : UIViewController {
weak var firstViewController : ViewController?
// Other code
func textFieldShouldReturn(nameEntry: UITextField) -> Bool
{
firstViewController?.colourLabel.text = nameEntry.text
nameEntry.resignFirstResponder()
dismissViewControllerAnimated(true, completion: nil)
return true
}
}
Inside First View Controller prepareForSegue
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if segue.identifier == "SecondViewController" {
let secondViewController = segue.destinationViewController as SecondViewController
secondViewController.firstViewController = self
}
}
It's possible that the view controller returned by ViewController() has not yet loaded its views. You could try checking this in a setter function and storing it for later use once the views have been loaded.
class VC : UIViewController {
#IBOutlet weak var colourLabel: UILabel!
var savedLabelText: String?
override func viewDidLoad() {
super.viewDidLoad()
self.colourLabel.text = self.savedLabelText
}
func setColorLabelText(label: String) {
if self.isViewLoaded() {
self.colourLabel.text = label
}
else {
self.savedLabelText = label
}
}
}
Related
I need to pass a String and Array from my Third ViewController to my First ViewController directly using protocol/delegate, I have no problem doing it from VC 2 to VC 1 but I'm having a hard time with this. Also after clicking a button in my VC3 I need to go back to VC 1 and update the VC UI how would I do that? Would that have to be in viewdidload?
This in Swift UIKit and Storyboard
You need two protocols, and your firstVC and SecondVC have to conform those. When pushing new ViewController you need to give the delegate of that ViewController to self. On your third VC, when you click the button you need to call your delegate and pass your data to that delegate method, then repeat the same for other.
For FirstVC
protocol FirstProtocol: AnyObject {
func firstFunction(data: String)
}
class FirstVC: UIViewController, FirstProtocol {
weak var delegate: FirstProtocol?
#IBAction func buttonClicked(_ sender: Any) {
let secondVC = SecondVC()
secondVC.delegate = self
navigationController?.pushViewController(secondVC, animated: true)
}
func firstFunction(data: String) {
navigationController?.popToRootViewController(animated: true)
print(data)
}
}
You handle your navigation from your root. For better experience you can use something like coordinator pattern to handle it.
protocol SecondProtocol: AnyObject {
func secondFunction(data: String)
}
class SecondVC: UIViewController, SecondProtocol {
weak var delegate: FirstProtocol?
#objc func buttonClicked() {
let thirdVC = ThirdVC()
thirdVC.delegate = self
navigationController?.pushViewController(thirdVC, animated: true)
}
func secondFunction(data: String) {
delegate?.firstFunction(data: data)
}
}
Second VC is something that you just need to pass parameters.
class ThirdVC: UIViewController {
weak var delegate: SecondProtocol?
#objc func buttonClicked() {
delegate?.secondFunction(data: "data") // PASS YOUR ARRAY AND STRING HERE
}
}
What you need is unwind segue. Unwind segue will act like segue, only backward, popping, in this case, VC2. You can read here for more information.
Updating data code would be put in a function similar to prepareToSegue() but for unwind segue in your VC1.
Example of the function inside VC1:
#IBAction func unwindToDestination(_ unwindSegue: UIStoryboardSegue) {
switch unwindSegue.identifier {
case SegueIdentifier.yourSegueIdentifier:
let sourceVC = unwindSegue.source as! SourceVC
dataToPass = sourceVC.dataToPass
reloadData()
default:
break
}
}
Here is a different approach that accomplishes what you described by performing a Present Modally segue directly from View Controller 3 to View Controller 1, and sharing the string and array values by way of override func prepare(for segue....
In Main.storyboard, I set up 3 View Controllers, and have segues from 1 to 2, 2 to 3, and 3 to 1. These are Action Segues directly from the buttons on each VC, which is why you won't see self.performSegue used inside any of the View Controller files. Here is the picture:
In the first view controller, variables are initialized (with nil values) that will hold a String and an Array (of type Int in the example, but it could be anything):
import UIKit
class FirstViewController: UIViewController {
#IBOutlet weak var updatableTextLabel: UILabel!
var string: String?
var array: [Int]?
override func viewDidLoad() {
super.viewDidLoad()
// These will only not be nil if we came here from the third view controller after pressing the "Update First VC" button there.
// The values of these variables are set within the third View Controller's .prepare(for segue ...) method.
// As the segue is performed directly from VC 3 to VC 1, the second view controller is not involved at all, and no unwinding of segues is necessary.
if string != nil {
updatableTextLabel.text = string
}
if let a = array {
updatableTextLabel.text? += "\n\n\(a)"
}
}
}
The second view controller doesn't do anything except separate the first and third view controllers, so I didn't include its code.
The third view controller assigns the new values of the string and array inside prepare (this won't be done unless you press the middle button first, to demonstrate both possible outcomes in VC 1). This is where your string and array get passed directly from 3 to 1 (skipping 2 entirely).
import UIKit
class ThirdViewController: UIViewController {
var theString = "abcdefg"
var theArray = [1, 2, 3]
var passValuesToFirstVC = false
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func updateFirstVC(_ sender: UIButton) {
passValuesToFirstVC = true
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if passValuesToFirstVC && segue.identifier == "toFirst" {
// Cast segue.destination (which on its own has type UIViewController, the superclass to all your custom View Controllers) to the specific subclass that your first View Controller belongs to
let destinationVC = segue.destination as! FirstViewController
// When your first view controller loads, it will receive these values for the 'string' and 'array' variables. They replace the original 'nil' values these had in the FirstViewController definition.
destinationVC.string = theString
destinationVC.array = theArray
}
}
}
Note that there is an IBOutlet to the label on the first View Controller which contains the text to be updated.
After visiting the third view controller, pressing the "Update First VC Text" button, and then performing the segue back to the first, here is how it will look:
This doesn't address the part about protocols and delegates in your question (as I'm not sure how they're being used in your program, and other answers have already addressed that), but it illustrates the method of transferring variables directly from one View Controller to another without unwinding segues or using the UINavigationController.
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 have an app setup to have a Master root viewController with a Navigation bar that has a "Settings button". When the user taps the settings button, it brings up a 'settingsTableViewController' that is not dynamic, but rather static so i can format the tableviews with settings like style.
in this settings view, i have a UITextField that takes a Person's name.
When the user clicks "Done" in the navigation bar, i want to pass that name back to the Master Root ViewController so i can use it in the title to display the Person's name. (I want to pass the name upon dismissing the view)
I have tried to use segue's but no luck. Here is a bit of what i tried.
SettingsViewController (pop's over the MasterVC)
class SettingsTableViewController: UITableViewController {
#IBOutlet weak var nameTextfield: UITextField!
#IBAction func done(sender: AnyObject) {
self.dismissViewControllerAnimated(true, completion: nil)
}
override viewDidLoad(){
self.title = "Settings"
}
// MARK: - Navigation
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
// Trying to pass what was typed in the textfield to the Root ViewController and store this name in a variable of type String called 'name'
if segue.identifier == "masterView"{
let masterViewController = segue.destinationViewController as! MasterTableViewController
masterViewController.name = nameTextField.text
print("Segue was used")
}
}
}
MasterTableViewController.swift
class MasterTableViewController: UITableViewController {
var name: String!
// I am trying to then display the name entered in the pop-over view in this root view controller's title
override viewDidLoad(){
self.title = name!
}
}
My question is, what did i do wrong? I have tried to use delegation but i get nil and the data doesn't seem to get passed either way so any leads will greatly help. Thanks
There is a different kind of segue called Unwind Segue to do that. It doesn't create a new mvc and its used to pass data back to the vc that presented the current one. here is how to do it
First, go to your storyboard and control drag from settingVc to the exit button on top of it (to itself). it will give you 'Selection Segue' and choose IBAction goBack. This means any vc that presented the current one will get to prepare if they implement this method. In other words, you're putting out a protocol and the presenter vc will conform by implementing goBack IBAction. here is how to implement that. In your Mater vc
//You must have this function before you do the segue in storyboard
#IBAction func goBack(segue: UIStoryboardSegue){
/* this is optional
if let stv = segue.sourceViewController as? SettingsTableViewController{
self.name = stv.nameTextfield?.text
}
*/
}
In your setting vc (current vc)
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
//make sure you set the id of your segue to "Your Go back Unwind segue". ofc u can name it whatever
if segue.identifier == "Your Go back Unwind segue"{
if let mtvc = segue.destinationViewController as? MasterTableViewController{
mtvc.name = nameTextField.text
print("Segue was used")
}
}
}
and done method should be something like this
#IBAction func doneEditing(sender: UIButton) {
presentingViewController?.dismissViewControllerAnimated(true, completion: nil)
}
I have a program in which the user will enter data in one view controller and the information is calculated in another. I've gotten to the point where I can enter the data and when I segue to the SecondViewController I can access my data. But when I switch back to the first ViewController, the UITextFields are blank because the ViewController is re-instantiated.
Basically my application so far has one ViewController with two UITextfields and a SecondViewController that shows the data. I need a way to save the instance of the first ViewController when I am switching between the two.
I've tried using the answer from iOS Swift, returning to the same instance of a view controller , but yourVariable cannot be set to nil, so I got stuck there.
This is my code for segue-ing from the first ViewController to the SecondViewController
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?)
{
if (segue.identifier == "Show")
{
var destinationVC = segue.destinationViewController as! MainViewController
}
}
I only have a button that I press to go back to the first ViewController.
You can create a class to store your text file, create instance of it in appdelegate(in a global scope) and get your text data to the textfield using observer. global instance of a class may not be the best choice if your app is not as simple as you described it in which case you can use NSUsersDefault to save it as plist. I hope I helped :)
//in first view controller
#IBOutlet weak var textfield: UITextField!{
didSet{
textfield.text = text
}
}
var text:String = ""{
didSet{
textfield?.text = text
}
}
func override viewWillAppear(animated: Bool) {
//set value of text from your global class instance or
//decode it here from the archive file if you used NSUsersDefault
text =
}