I am trying to familiarize with swift but I can't find how to pass data between views using Swift.
class ViewController: UIViewController {
#IBOutlet var field: UITextField
#IBOutlet var butt: UIButton
override func prepareForSegue(segue: UIStoryboardSegue!, sender: AnyObject!) {
if let vc = segue.destinationViewController as? secondViewController {
if(vc.lab != nil){
vc.lab.text=self.field.text
println(self.field.text)
}
}
and second view controller:
class secondViewController: UIViewController {
#IBOutlet var lab: UILabel
override func viewDidLoad() {
super.viewDidLoad()
}
What I want to do is simply change the label in the second view with the text of the textfield of the first view.
In this way does not give me any error but I do not change the label.
To me, this doesn't look like a Swift problem. It looks like a view lifecycle problem. At the time prepareForSegue: is called, the secondViewController has not loaded it's IBOutlets from the storyboard yet. A better solution would be to set some type of property on the file, like
vc.myLabelString = self.field.text
then in viewDidLoad of secondViewController assign the text to your label.
FYI: You can always check if a view controller has loaded it's view with vc.isViewLoaded()
Related
I have an app written in Swift for iOS 13 where I present a view modally using storyboards. Once the new view is being presented, I want the parent to call a method which is located inside the child view controller (of my custom class which inherits from UIViewController).
To do this, I plan to have a method inside my parent view controller that gets the modal view controller being presented as its child. Once I get this reference, I will call the child's function from my parent view controller.
I realise this is probably a bad design decision, but I haven't found a way to avoid this approach. I have looked all over stackoverflow to find an answer, but I haven't found any yet. Any help would be much appreciated.
You can instantiate the child view controller and set its properties before presenting it. Then the code that changes the child view controller based on the data is put in the viewDidLoad() method.
class ParentViewController: UIViewController {
func goToChildViewController(object: CustomObject) {
guard let childViewController = self.storyboard?.instantiateViewController(withIdentifier: "child") as? ChildViewController else { fatalError("Cannot instantiate child view controller!") }
childViewController.myProperty = true
childViewController.myObject = myObject // Example of how to pass data from a data model
self.present(childViewController, animated: true)
}
}
class ChildViewController: UIViewController {
var myProperty = false
var myObject: CustomObject? = nil
override viewDidLoad() {
if myProperty {
// Conditional code here
}
{
}
Alternatively, you could trigger a segue in code instead of presenting the child view controller directly.
In this case, you would set up the child view controller inside the parent view controller’s overridden prepare(for:sender:) method, where the child view controller can be accessed using segue.destinationViewController.
Through Segue
When segue triggered maybe through a button press or a table view selection prepare(for:) method will be called on your view controller, at this point you can configure your DestinationViewController by setting some properties.
RootViewController.Swift
#IBOutlet weak var textFieldFirstName: UITextField!
#IBOutlet weak var labelFullname: UILabel!
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
guard let firstVC = segue.destination as? FirstViewController else { return }
firstVC.firstname = textFieldFirstName.text
}
After typing the firstname and tap enter button , firstname value is passed to firstViewController and assigned to related UILabel in viewDidLoad() Method.
FirstViewController.Swift
#IBOutlet weak var textFieldLastName: UITextField!
#IBOutlet weak var labelFirstName: UILabel!
var firstname: String?
override func viewDidLoad() {
super.viewDidLoad()
labelFirstName.text = “Firstname: \(firstname ?? “”)”
}
You can achieve same thing through closure and Delegates
does anyone know how to pass an action from ViewController to its ContainerViewController. I try to hide the container view by an action that is triggered by itself. The ContainerViewController is embedded in the container view.
ViewController:
#IBOutlet weak var ChoseLanguageContainer: UIView!
**ContainerViewController:**
#IBAction func action(_ sender: Any) {
ViewController().containerView.isHidden = true
} //I know this does not work
I had the similar requirement, I created my own delegate methods which were implemented in ContainerViewController.
protocol ContainerViewControllerDelegate :class{
func notifyItemChange(any params you need to pass.)
}
In my container ViewController, I created a variable for delegate.
var changeContainerDelegate :ContainerViewControllerDelegate?
In my parent View Controller which contains the container, I did the following.
To get the instance of view controller which is embedded in the container.
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if let containerViewController = segue.destination as? ContainerViewController{
containerViewController.changeContainerDelegate = self
}
Create IBOutlet of container view in your view controller.
Conform to this protocol and write the implementation in View controller.
func changeContainerVC(containerVCName : String ,dataToBePassed:[AnyObject]?) {
containerView.isHidden = true
}
In the button action inside the ContainerViewController call the delegate like :
changeContainerDelegate?.notifyItemChange()
This works for me. Hope helps ou too!
In your code:
ViewController().containerView.isHidden = true
You are making a new instance of the ViewController and using it to hide the containerView. This won't work. Instead you need to hide the containerView of the current instance of ViewController, i.e self.
Here is the code you can try:
class ViewController: UIViewController
{
#IBOutlet weak var containerView: UIView!
override func viewDidLoad()
{
super.viewDidLoad()
}
#IBAction func hideContainerView(_ sender: UIButton)
{
self.containerView.isHidden = true
}
}
View Hierarchy:
Let me know if you face any other issue regarding this.
I am trying create Tab Bar application. I added to the first viewcontroller a button and a text field. When I wrote some text and pushed button I expected that loads second viewcontroller and in the label field appears text from the text field.
I have 2 problems.
Second viewcontroller loaded twice.
when I push button on tab bar and load first viewcontroller again? me text disappear.
I only start work with Xcode. Help me please and describe resolve in details🙏
import UIKit
var tfTextString: String = ""
class FirstViewController: UIViewController {
#IBOutlet weak var textField: UITextField!
#IBAction func enter(_ sender: Any) {
if textField.text != "" {
//performSegue(withIdentifier: "segue", sender: self)
//tfTextString = textField.text!
self.tabBarController?.selectedIndex = 0
}
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
var secondController = segue.destination as! SecondViewController
secondController.myString = textField.text!
}
}
import UIKit
class SecondViewController: UIViewController {
#IBOutlet weak var label: UILabel!
var myString = String()
override func viewDidLoad() {
super.viewDidLoad()
label.text = myString
}
}
It looks like your view controller is loaded twice because you are loading it twice.
Don't think of each screen on the storyboard as being it's own distinct entity as per the singleton pattern. They aren't. They're their own distinct class / view combination, which gets instantiated (loaded) once every time you call it. To put it another way, you aren't looking at the 'actual' classes in the storyboard, you're looking at the template that's used to build the class when called for. So you're calling for it twice, in two different places, and it happily produces multiple copies of the underlying view / controller for you.
I think you don't want to use a navigation controller to 'push' the view back onto the stack. You're going to want to tell the tab bar to switch to a different view instead.
The swift version of the code you're looking for is:
self.tabBarController?.selectedIndex = 1
I think the objective-C equivalent would have been...
[[self tabBarController] setSelectedIndex:1];
But it's been long enough since I've done swift I may have overlooked something important in there.
App has two View Controllers: ViewController (this is the main View Controller that displays the majority of the app's content) and SecondViewController (accessible via a UIButton on ViewController; SecondViewController is only used to display a user's inventory, and a UIButton within SecondViewController allows the user to return to the original view, ViewController). Currently, the app uses the "Show" action segue to switch between View Controllers when the user presses the appropriate UIButton. However, after switching from ViewController to SecondViewController, and then pressing the UIButton to return to ViewController, the properties of ViewController have been reverted to the properties that occur when the app launches (background color is changed, certain text fields appear that shouldn't).
So, how do I "save the state" of ViewController when the user moves to SecondViewController, so that the user resumes where they left off when they return to ViewController?
What you are looking for is an unwind segue. Here's the simplest way of how to create it:
In your ViewController (or, basically any other view controller you are willing to pop to) create an IBAction that accepts an instance of a segue (function name doesn't really matter):
#IBAction func unwindToThisVC(segue: UIStoryboardSegue) { }
In the storyboard, go to SecondViewController, and control + drag from your UIButton to the Exit outlet of ViewController and then select the IBAction you've created in step 1:
More on Unwind Segues
The way you are doing it now (using Show from the second to get back to the first) actually brings up a third VC.
What you want to do is dismiss the second view controller.
The normal way is to implement a protocol for the second one that the first one implements and then to have a function in that protocol for the second one to let the first one know it is done.
When the function is called, the first one dismisses the second and then it will be shown again with its state intact.
Here is a simple example of segue and unwind that you can adapt to your problem... Assume that you have ViewController with label and a button and a SecondViewController with label and a button.
For the first ViewController...
import UIKit
//steps to receive data back from SecondViewController...
//1. create protocol in the SecondViewController (see SecondViewController code)
//2. conform to the protocol
class ViewController: UIViewController, UnwindSegue {
//3. method that gets triggred.
func dataReceived(dataSegued: String) {
labelOne.text = dataSegued
}
#IBOutlet weak var textField: UITextField!
#IBOutlet weak var labelOne: UILabel!
var textReceived : String = ""
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
#IBAction func btPressed(_ sender: Any) {
performSegue(withIdentifier: "goToSecondController", sender: self)
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "goToSecondController" {
let destinationVC = segue.destination as! SecondViewController
destinationVC.textSegued = textField.text!
//4. create delegate in the SecondViewController (see SecondViewController code)
//5. set ourselves up as delegate of SecondViewController
destinationVC.delegate = self
//6. then dismiss the SecondViewController (see SecondViewController code)
}
}
}
Then for your SecondViewController...
import UIKit
//1. create protocols and delegates to transfer data back
protocol UnwindSegue {
//single required method with a single parameter
func dataReceived(data:String)
}
class SecondViewController: UIViewController {
var textSegued : String?
//4. create delegate of the protocol of type CanReceive that can be a nil. If it is nil, it doesn't go anywhere when BT is pressed
var delegate : UnwindSegue?
#IBOutlet weak var label: UILabel!
#IBOutlet weak var secondTextField: UITextField!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
label.text = textSegued
}
#IBAction func btTwoPressed(_ sender: Any) {
//this is not triggered if var delegate is nil (as defined as optional)
delegate?.dataReceived(data: secondTextField.text!)
//6. dismiss the 2nd VC so you can see the fist VC
dismiss(animated: true, completion: nil)
}
}
DetailViewController:
#IBOutlet var selectedBundesland: UILabel!
TableViewController:
override func prepareForSegue(segue: UIStoryboardSegue!, sender: AnyObject!) {
if (segue.identifier == "BackToCalculator") {
var vc:FirstViewController = segue.destinationViewController as FirstViewController
vc.selectedBundesland.text = "Test"
}
IBOutlet is connected!
Error: fatal error: unexpectedly found nil while unwrapping an Optional value
I read multiple pages about Optionals but i didn't know the answer to my problem.
Do you need more information about my project?
You cannot write directly to the UILabel in prepareForSegue because the view controller is not fully initialised yet. You need to create another string property to hold the value and put it into the label in the appropriate function - such as viewWillAppear.
DetailViewController:
var textValue: String = ""
#IBOutlet weak var selectedBundesland: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
selectedBundesland.text = textValue
}
TableViewController:
if (segue.identifier == "BackToCalculator") {
var vc:FirstViewController = segue.destinationViewController as FirstViewController
vc.textValue = "Test"
}
Recently had this problem. The problem was that I had dragged the segue from a specific object from my current view controller to the destination view controller - do not do this if you want to pass values.
Instead drag it from the yellow block at the top of the window to the destination view controller. Then name the segue appropriately.
Then use the if (segue.identifier == "BackToCalculator") to assign the value as you are currently. All should work out!
I just had the same problem, I solved it by defining a string that is not connected to an outlet in the new view controller and than referring to it in the prepareForSegue() method, in the new VC I made the label outlet to take the value of the non connected string in the viewDidLoad() method.
Cheers
While the correct solution is to store the text and attach it to the label later in viewDidLoad or something, for testing proposes, you can bypass the issue by forcing the destinationViewController to build itself from storyboard by calling its view property like:
override func prepare(for segue: UIStoryboardSegue, sender: Any?){
if (segue.identifier == "TestViewController") {
var vc:FirstViewController = segue.destination as! TestViewController
print(vc.view)
vc.testLabel.text = "Hello World!"
}
}
made for Swift 3.0 with love