In ViewController.swift, I have a text field whose input I would like to use and manipulate in my other class, Conjugate.swift. I am capturing the input at the same time the keyboard is hidden, like so:
import UIKit
class MainViewController: UIViewController, UITextFieldDelegate {
#IBOutlet weak var mainTextField: UITextField!
var input: String!
override func viewDidLoad() {
super.viewDidLoad()
mainTextField.delegate = self
}
/* KEYBOARD HIDE */
func textFieldShouldReturn(textField: UITextField) -> Bool {
input = self.mainTextField.text
textField.resignFirstResponder()
return true;
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
}
And then in my other class:
class Conjugate {
var infinitive: String!
var isEndingAr = false
func conjugate() {
// gets verb from text field
infinitive = MainViewController().input
// checks verb ending and sets value to booleans
if (infinitive.hasSuffix("ar")) {
isEndingAr = true
}
}
}
Here is the error I'm getting:
fatal error: unexpectedly found nil while unwrapping an Optional value
I know that input in MainViewController.swift is still nil. I just don't know why. What am I doing wrong?
When you do infinitive = MainViewController().input, MainViewController() just creates a new instance of MainViewController. That new instance never calls textFieldShouldReturn and therefore its input will be nil. Instead, add a reference from Conjugate to MainViewController.
var mainViewController: MainViewController?
Then in textFieldShouldReturn create a Conjugate and assign its property:
let conjugate = Conjugate()
conjugate.mainViewController = self
Then in the conjugate() method, instead of creating a new view controller, refer to the property:
func conjugate() {
// gets verb from text field
infinitive = self.mainViewController!.input!
// checks verb ending and sets value to booleans
if (infinitive.hasSuffix("ar")) {
isEndingAr = true
}
}
}
Also, like #emresancaktar said, input should be optional, since it might be nil. However, infinitive does not have to be optional.
Related
I want to implement the MVP pattern for a new app. So the View shouldn't have any logic besides one that exclusively concerns UI elements. Therefore I want to request initial data from an "Interpreter" (interpreting user input in later code), which in turn requests data from my model and gives it to the "Presenter". The presenter holds a protocol with functions of the view.
The problem is: Calling updateUIData() from the presenter results in a
fatal error: unexpectedly found nil while unwrapping an Optional value
while calling the function from within the View at the same position is working just fine.
I suspect the error comes from the initialization of the specific MainViewController in the init of the presenter, but I don't know how to resolve this, if my guess is right.
Here's my (relevant) code:
MainViewController:
class MainViewController: UIViewController {
lazy var interpreter = Interpreter() // lazy needed b/c Interpreter holds Presenter which holds MainViewController
#IBOutlet var dateLabel: UILabel!
#IBOutlet var totalTimeLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
// updateUIData()
requestData()
}
func requestData() {
interpreter.requestData()
}
}
extension MainViewController: MainViewSetters {
func updateUIData() {
dateLabel.text = "Data"
totalTimeLabel.text = "loaded"
}
}
MainViewSetters (Protocol):
protocol MainViewSetters {
func updateUIData()
}
Interpreter:
class Interpreter {
let presenter = Presenter()
func requestData() {
// normally: get data from model and pass it to presenter
presenter.presentData()
}
}
Presenter:
class Presenter {
let mainView: MainViewSetters
init(withMainViewController mainVC: MainViewSetters = MainViewController()) {
mainView = mainVC
}
func presentData() {
mainView.updateUIData()
}
}
Your problem here is that you are not passing the reference to MainViewController to your instance of Presenter.
This code :
lazy var interpreter = Interpreter()
Should be more like this : (Type is needed here because with lazy the compiler can't infer properly)
lazy var interpreter: Interpreter = Interpreter(for: self)
You then have to create a special initializer in Interpreter which will pass the viewController instance to its presenter property :
class Interpreter {
let presenter: Presenter
init(for viewController: MainViewSetters) {
presenter = Presenter(withMainViewController: viewController)
}
func requestData() {
// normally: get data from model and pass it to presenter
presenter.presentData()
}
}
I also highly suggest you to remove the default value to Presenter's init method, it's very unlikely you'll want to assign a random instance of MainViewController as mainView of any Presenter object.
Finally, please note that this code is creating a retain cycle and neither your MainViewController instance nor your Presenter instance will be deallocated. This is due to the fact the Presenter class holds a strong reference to the MainViewController instance with its property mainView. To fix this you have to mark the mainView as weak as well as making it optional.
Please see the fixed implementation below :
class Presenter {
weak var mainView: MainViewSetters?
init(withMainViewController mainVC: MainViewSetters) {
mainView = mainVC
}
func presentData() {
mainView?.updateUIData()
}
}
For weak to be acceptable on a property of type MainViewSetters (which is not a real type but only a protocol) you have to specify that its a protocol that will only be applied to classes :
protocol MainViewSetters: class {
func updateUIData()
}
You are initializing interpreter passing a default MainViewController().
Change that code from:
lazy var interpreter = Interpreter()
to
lazy var interpreter = Interpreter(withMainViewController: self)
When dialing with CocoaTouch, it often happens that UIView(Controller) subclass properties can't be initialized in init method (ex. we need view already loaded), but logically they are non-optional and even non-var. In such cases the property must be optional to compile without errors, what looks pretty ugly - the code is fulfilled with !.
Is there any way to solve this problem? I would imagine some deferred initialization. Perfectly if such property can compile without initial value and crash at runtime if it's accessed prior to be initialized.
Some code sample to describe the issue:
class MyVC: UIViewController {
#IBOutlet var someLabel: UILabel!
let viewBasedParam: CustomClass // how to keep it non-optional if it can be initialized after view has been loaded?
override func viewDidLoad() {
super.viewDidLoad()
self.viewBasedParam = CustomClass(self.someLabel.text)
}
}
P.S. CustomClass can't have default initializer, because it requires data from view.
In your MyVC you can have a convenience init method where you can initialize the let variables. Try this and let me know if it works for you:
class MyVC: UIViewController {
let viewBasedParam: CustomClass
convenience init() {
self.init(nibName:nil, bundle:nil)
self.viewBasedParam = CustomClass(self.someLabel.text)//else just initialize with empty string here and then assign actual value in viewDidLoad
}
}
As far as I've discovered the workaround solution may be following:
class MyVC: UIViewController {
#IBOutlet var someLabel: UILabel!
private var _viewBasedParam: CustomClass? = nil
var viewBasedParam: CustomClass {
get { return self._viewBasedParam! } // always unwrap private optional
set { self._viewBasedParam = newValue }
}
override func viewDidLoad() {
super.viewDidLoad()
self.viewBasedParam = CustomClass(self.someLabel.text)
}
}
Currently working with two view controllers and a swift file dealing with the details of a store such as the phone number. There is a main ViewController and a DetailsViewController.
I currently acquire data from google places api and am able to successfully store the values in a PlaceDetails Class. Testing out the data - I am able to print to the console. However, when I try to assign a value taken from the API to a UILabel the application crashes and shows that the value of the property is nil. I am not sure why this is the case. I feel in the two view controllers I am instantiating the PlaceDetails class correctly and accessing it's properties correctly but there is something I am not aware of that is going wrong.
class ViewController: UIViewController
{
let placeDetails = PlaceDetails()
let detailsVC = DetailsViewController()
func tapLabel( sender: UITapGestureRecognizer )
{
// print statement successfully prints out the stored value as - Optional("1 888-555-5555")
print(placeDetails.phoneNumber)
// assigning value to label causes a crash stating value is nil
detailsVC.phoneNumberLabel.text = placeDetails.phoneNumber!
self.performSegueWithIdentifier("showDetailsVC", sender: self)
}
}
class DetailsViewController: UIViewController
{
#IBOutlet weak var phoneNumberLabel : UILabel!
let placeDetails = PlaceDetails()
override func viewDidLoad()
{
super.viewDidLoad()
//This approach does not cause a crash but outputs nil to the console for both the print statement and the assignment statement
print(placeDetails.phoneNumber)
phoneNumberLabel.text = placeDetails.phoneNumber!
}
}
class PlaceDetails
{
override init()
{
super.init()
}
var phoneNumber : String? //viewcontroller actions give this class property its value
}
You need to assign placeDetails to your destination view controller in prepareForSegue. I know you aren't doing this as you have created placeDetails as a let constant rather than a variable so it can't ever change from the empty PlaceDetails you originally assign.
You should declare it as an optional variable and then unwrap it properly when you use it;
class ViewController: UIViewController
{
let placeDetails = PlaceDetails()
func tapLabel( sender: UITapGestureRecognizer )
{
self.performSegueWithIdentifier("showDetailsVC", sender: self)
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject!) {
if (segue.identifier == "showDetailsVC") {
let destVC = segue.destinationViewController as! DetailsViewController
destVC.placeDetails = self.placeDetails
}
}
}
class DetailsViewController: UIViewController
{
#IBOutlet weak var phoneNumberLabel : UILabel!
var placeDetails: PlaceDetails?
override func viewWillAppear(animated: Bool)
{
super.viewWillAppear(animated)
if let placeDetails = self.placeDetails {
if let phoneNumber = placeDetails.phoneNumber {
self.phoneNumberLabel.text = phoneNumber
}
}
}
}
You can't use the value in viewDidLoad as this method will execute before the property has been set; the view controller is loaded before prepareForSegue is called, so viewWillAppear is a better place.
Try to cast your phoneNumber in a string.
detailsVC.phoneNumberLabel.text = String(placeDetails.phoneNumber!)
Also, the nil value could come from the encoding method of the response of the API.
EDIT
I think you have to set the text of your UILabel in the viewDidLoad() method of your showDetailsVC. Declare a string variable in showDetailVC, and then pass your placeDetails.phoneNumber variable to the string you just declare. (Instead of directly set the text in the tapLabel() method). Then in your
showDetailVC set the text to your UILabel in the viewDidLoad()
I need to execute a function when a variable value changes.
I have a singleton class containing a shared variable called labelChange. Values of this variable are taken from another class called Model. I have two VC classes, one of them has a button and a label and the second only a button.
When the button in the first VC class is pressed I am updating the label with this func:
func updateLabel(){
self.label.text = SharingManager.sharedInstance.labelChange
}
But I want to call the same method whenever the value of the labelChange is changed. So in button click I will only update the labelChange value and when this thing happen I want to update the label with the new value of the labelChange. Also in the second VC I am able to update the labelChange value but I am not able to update the label when this value is changed.
Maybe properties are the solution but can anyone show me how to do so.
Edited second time:
Singleton Class:
class SharingManager {
func updateLabel() {
println(labelChange)
ViewController().label.text = SharingManager.sharedInstance.labelChange
}
var labelChange: String = Model().callElements() {
willSet {
updateLabel()
}
}
static let sharedInstance = SharingManager()
}
First VC:
class ViewController: UIViewController {
#IBOutlet weak var label: UILabel!
#IBAction func Button(sender: UIButton) {
SViewController().updateMessageAndDismiss()
}
}
Second VC:
func updateMessageAndDismiss() {
SharingManager.sharedInstance.labelChange = modelFromS.callElements()
self.dismissViewControllerAnimated(true, completion: nil)
}
#IBAction func b2(sender: UIButton) {
updateMessageAndDismiss()
}
I made some improvements but I need to reference a label from the first VC class in singleton. Therefore I will update that label of VC in singleton.
When I print the value of labelChange the value is being updated and everything is fine. But when I try to update that value on label from singleton I receive an error:
unexpectedly found nil while unwrapping an Optional value
and the error is pointing in 4th line of singleton class.
You can simply use a property observer for the variable, labelChange, and call the function that you want to call inside didSet (or willSet if you want to call it before it has been set):
class SharingManager {
var labelChange: String = Model().callElements() {
didSet {
updateLabel()
}
}
static let sharedInstance = SharingManager()
}
This is explained in Property Observers.
I'm not sure why this didn't work when you tried it, but if you are having trouble because the function you are trying to call (updateLabel) is in a different class, you could add a variable in the SharingManager class to store the function to call when didSet has been called, which you would set to updateLabel in this case.
Edited:
So if you want to edit a label from the ViewController, you would want to have that updateLabel() function in the ViewController class to update the label, but store that function in the singleton class so it can know which function to call:
class SharingManager {
static let sharedInstance = SharingManager()
var updateLabel: (() -> Void)?
var labelChange: String = Model().callElements() {
didSet {
updateLabel?()
}
}
}
and then set it in whichever class that you have the function that you want to be called, like (assuming updateLabel is the function that you want to call):
SharingManager.sharedInstance.updateLabel = updateLabel
Of course, you will want to make sure that the view controller that is responsible for that function still exists, so the singleton class can call the function.
If you need to call different functions depending on which view controller is visible, you might want to consider Key-Value Observing to get notifications whenever the value for certain variables change.
Also, you never want to initialize a view controller like that and then immediately set the IBOutlets of the view controller, since IBOutlets don't get initialized until the its view actually get loaded. You need to use an existing view controller object in some way.
Hope this helps.
In Swift 4 you can use Key-Value Observation.
label.observe(\.text, changeHandler: { (label, change) in
// text has changed
})
This is basically it, but there is a little catch. "observe" returns an NSKeyValueObservation object that you need to hold! - when it is deallocated, you’ll receive no more notifications. To avoid that we can assign it to a property which will be retained.
var observer:NSKeyValueObservation?
// then assign the return value of "observe" to it
observer = label.observe(\.text, changeHandler: { (label, change) in
// text has changed,
})
You can also observe if the the value has changed or has been set for the first time
observer = label.observe(\.text, changeHandler: { (label, change) in
// just check for the old value in "change" is not Nil
if let oldValue = change.oldValue {
print("\(label.text) has changed from \(oldValue) to \(label.text)")
} else {
print("\(label.text) is now set")
}
})
For More Information please consult Apples documentation here
Apple provide these property declaration type :-
1. Computed Properties:-
In addition to stored properties, classes, structures, and enumerations can define computed properties, which do not actually store a value. Instead, they provide a getter and an optional setter to retrieve and set other properties and values indirectly.
var otherBool:Bool = false
public var enable:Bool {
get{
print("i can do editional work when setter set value ")
return self.enable
}
set(newValue){
print("i can do editional work when setter set value ")
self.otherBool = newValue
}
}
2. Read-Only Computed Properties:-
A computed property with a getter but no setter is known as a read-only computed property. A read-only computed property always returns a value, and can be accessed through dot syntax, but cannot be set to a different value.
var volume: Double {
return volume
}
3. Property Observers:-
You have the option to define either or both of these observers on a property:
willSet is called just before the value is stored.
didSet is called immediately after the new value is stored.
public var totalSteps: Int = 0 {
willSet(newTotalSteps) {
print("About to set totalSteps to \(newTotalSteps)")
}
didSet {
if totalSteps > oldValue {
print("Added \(totalSteps - oldValue) steps")
}
}
}
NOTE:- For More Information go on professional link
https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Properties.html
There is another way of doing so, by using RxSwift:
Add RxSwift and RxCocoa pods into your project
Modify your SharingManager:
import RxSwift
class SharingManager {
static let sharedInstance = SharingManager()
private let _labelUpdate = PublishSubject<String>()
let onUpdateLabel: Observable<String>? // any object can subscribe to text change using this observable
// call this method whenever you need to change text
func triggerLabelUpdate(newValue: String) {
_labelUpdate.onNext(newValue)
}
init() {
onUpdateLabel = _labelUpdate.shareReplay(1)
}
}
In your ViewController you can subscribe to value update in two ways:
a. subscribe to updates, and change label text manually
// add this ivar somewhere in ViewController
let disposeBag = DisposeBag()
// put this somewhere in viewDidLoad
SharingManager.sharedInstance.onUpdateLabel?
.observeOn(MainScheduler.instance) // make sure we're on main thread
.subscribeNext { [weak self] newValue in
// do whatever you need with this string here, like:
// self?.myLabel.text = newValue
}
.addDisposableTo(disposeBag) // for resource management
b. bind updates directly to UILabel
// add this ivar somewhere in ViewController
let disposeBag = DisposeBag()
// put this somewhere in viewDidLoad
SharingManager.sharedInstance.onUpdateLabel?
.distinctUntilChanged() // only if value has been changed since previous value
.observeOn(MainScheduler.instance) // do in main thread
.bindTo(myLabel.rx_text) // will setText: for that label when value changed
.addDisposableTo(disposeBag) // for resource management
And don't forget to import RxCocoa in ViewController.
For triggering event just call
SharingManager.sharedInstance.triggerLabelUpdate("whatever string here")
HERE you can find example project. Just do pod update and run workspace file.
var item = "initial value" {
didSet { //called when item changes
print("changed")
}
willSet {
print("about to change")
}
}
item = "p"
override var isHighlighted: Bool {
get { super.isHighlighted }
set {
super.isHighlighted = newValue
if newValue {
label.textColor = highlightedTextColor
contentView.backgroundColor = highlightedBackgroundColor
} else {
label.textColor = normalTextColor
contentView.backgroundColor = normalBackgroundColor
}
}
}
I'm trying to make a simple app that counts the characters of a textfield, but when the user inputs the text, the function that converts the user-inputed string into a var and the function that counts the characters are executed at once. Here's the code:
import UIKit
class ViewController: UIViewController {
#IBOutlet var myTextField : UITextField
#IBOutlet var userTextField : UITextField
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
myTextField.text = fullConstant
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
#IBAction func modifyMyVariable(sender : AnyObject) {
myVariable = userTextField.text
}
#IBAction func clickMe(sender : AnyObject) {
countCharacters(&fullConstant)
println(fullConstant)
myTextField.text = fullConstant
}
}
And here's the "OtherFile.swift" where the functions are located:
import Foundation
var fullConstant = "Type something!"
var myVariable = ""
func modifyMyVariable() {
println()
}
func countCharacters(inout fullConstant: String) {
let FirstPart = "There are "
let LastPart = " characters"
var numberOfCharacters = countElements(myVariable)
switch numberOfCharacters {
case 0 :
fullConstant = "There isn't any character yet"
case 1 :
fullConstant = "There is just one character"
default :
fullConstant = FirstPart + String(numberOfCharacters) + LastPart
}
}
Both functions execute as soon the userTextField is edited, but if the user inputs one character, the countCharacters function takes the var myVariable before it's modified by the function modifyMyvariable, so it doesn't count the last character added.
To solve this, I've thought that I could call the function countCharacters from the function modifyMyVariable, so the variable myVariable has already changed when it counts the characters.
Change the following and see if it's then easier to fix your problem.
You should always only link each event to one IBAction. Your IBActions shouldn't be named after what you're trying to do in them; they should be named after the event that triggers them. For example, "modifyMyVariable" should be called "textEdited" or similar.
In that "textEdited" method, do all the work you need to do. If you need to call another function, call it from there instead of linking to two IBActions.
Put code in your "OtherFile" inside a
class OtherFile {
}
block, and hold an instance to that class as a variable in your view controller. You want to avoid declaring global functions outside of classes.
Not related, but name your constants using camelCase with first letter lower case, just like your variables. So FirstPart should be firstPart.
Avoid using 'inout' as much as possible. Each language has it's conventions; in ObjC and Swift, pass in values needed to do work, and return values that result from that work. So:
func countCharacters(text: String) -> (String)
Putting it all together, your 'modifyMyVariable' function (which should really be called 'textEdited') will look something like this:
myVariable = userTextField.text
let characterCount = self.myOtherFileInstance.countCharacters(myVariable)
myTextField.text = characterCount
and the other function (clickMe) should be deleted.