How To Pass Data Back To Previous View Controller Swift?

How to Pass Data Back to Previous View Controller in Swift

In Swift, you can pass data back to a previous view controller by using the delegate pattern. This is a design pattern that allows two objects to communicate with each other without having to know each other’s implementation details.

To use the delegate pattern, you first need to create a delegate protocol. This protocol defines the methods that the view controller that is receiving the data will implement. For example, you might create a delegate protocol called `DataDelegate` with the following methods:

func didReceiveData(data: Any)

Once you have created the delegate protocol, you need to assign the view controller that is sending the data to the delegate of the view controller that is receiving the data. You can do this in the view controller’s `viewDidLoad()` method:

dataViewController.delegate = self

Now, you can send data to the previous view controller by calling the `delegate` property’s `sendData()` method:

delegate?.sendData(data)

The view controller that is receiving the data will then call the corresponding method in its delegate protocol. For example, if the delegate protocol is called `DataDelegate`, the view controller will call the `didReceiveData()` method.

In this article, we will show you how to use the delegate pattern to pass data back to a previous view controller in Swift. We will create a simple app with two view controllers: a list view controller and a detail view controller. The list view controller will display a list of items, and the detail view controller will display the details of a selected item. We will pass the selected item from the list view controller to the detail view controller.

Key Value Description
Method
dismiss(animated: true, completion: nil)
Dismissing the current view controller will automatically pass back any data that was set using the setViewControllers(_:animated:) method.
Property
presentingViewController
The presenting view controller can be accessed from the current view controller’s presentingViewController property. This property can be used to pass data back to the previous view controller by setting the delegate property of the presenting view controller.
Delegate The UINavigationControllerDelegate protocol defines a number of methods that can be used to pass data back to the previous view controller. The most common method for passing data back is the didDismissViewController(_:) method. This method is called when the current view controller is dismissed, and it provides a reference to the dismissed view controller as an argument.
func didDismissViewController(_ viewController: UIViewController) {
// Pass data back to the previous view controller.
}

What is Data Passing?

Data passing is the process of sending data from one part of a program to another. In Swift, data can be passed between view controllers using a variety of methods, including segues, closures, and delegates.

How to Pass Data Back in Swift?

There are three main ways to pass data back in Swift:

  • Using a segue
  • Using a closure
  • Using a delegate

Using a Segue

A segue is a transition between two view controllers. When you create a segue, you can specify a segue identifier. This identifier can be used to pass data from the source view controller to the destination view controller.

To pass data using a segue, you need to do the following:

1. In the source view controller, create a property to store the data you want to pass.
2. In the prepare(for segue: sender:) method of the source view controller, set the destination view controller’s property with the data you want to pass.
3. In the destination view controller, access the data that was passed by using the property you created in step 1.

Here is an example of how to pass data using a segue:

swift
class ViewController: UIViewController {

@IBOutlet weak var nameTextField: UITextField!

var name: String?

override func viewDidLoad() {
super.viewDidLoad()
}

@IBAction func onSubmitButtonTapped(_ sender: Any) {
let name = nameTextField.text

let destinationViewController = storyboard?.instantiateViewController(withIdentifier: “DestinationViewController”) as! DestinationViewController

destinationViewController.name = name

self.present(destinationViewController, animated: true, completion: nil)
}
}

class DestinationViewController: UIViewController {

@IBOutlet weak var nameLabel: UILabel!

var name: String?

override func viewDidLoad() {
super.viewDidLoad()

if let name = name {
nameLabel.text = name
}
}
}

Using a Closure

A closure is a function that can be passed around as a value. You can use a closure to pass data from one view controller to another.

To pass data using a closure, you need to do the following:

1. In the source view controller, create a closure to accept the data you want to pass.
2. In the prepare(for segue: sender:) method of the source view controller, call the closure with the data you want to pass.
3. In the destination view controller, access the data that was passed by using the closure.

Here is an example of how to pass data using a closure:

swift
class ViewController: UIViewController {

@IBOutlet weak var nameTextField: UITextField!

var name: String?

override func viewDidLoad() {
super.viewDidLoad()
}

@IBAction func onSubmitButtonTapped(_ sender: Any) {
let name = nameTextField.text

let destinationViewController = storyboard?.instantiateViewController(withIdentifier: “DestinationViewController”) as! DestinationViewController

destinationViewController.didReceiveName = { name in
self.name = name
}

self.present(destinationViewController, animated: true, completion: nil)
}
}

class DestinationViewController: UIViewController {

@IBOutlet weak var nameLabel: UILabel!

var didReceiveName: ((String) -> Void)?

override func viewDidLoad() {
super.viewDidLoad()

if let name = didReceiveName {
nameLabel.text = name
}
}
}

Using a Delegate

A delegate is a protocol that defines a set of methods that a class can implement to communicate with another class. You can use a delegate to pass data from one view controller to another.

To pass data using a delegate, you need to do the following:

1. In the source view controller, define a delegate protocol that defines the methods that the destination view controller will implement to receive the data.
2. In the source view controller, set the destination view controller’s delegate property to

3. Types of Data Passing

There are three main types of data passing in Swift:

  • Value passing
  • Reference passing
  • Closure passing

Value passing is the simplest type of data passing. When you pass a value to a function, the function receives a copy of the value. This means that any changes you make to the value inside the function will not affect the original value.

Reference passing is more complex than value passing. When you pass a reference to a value to a function, the function receives a reference to the original value. This means that any changes you make to the value inside the function will affect the original value.

Closure passing is a type of reference passing that allows you to pass a function as a value. This can be useful when you want to perform an operation on a value at a later time.

4. Best Practices for Data Passing

There are a few best practices to keep in mind when passing data between view controllers in Swift:

* **Use value passing whenever possible.** Value passing is the most efficient type of data passing, and it is also the safest.
* **Use reference passing when you need to make changes to the original value.** Reference passing is more efficient than value passing when you need to make changes to the original value.
* **Use closure passing when you need to perform an operation on a value at a later time.** Closure passing is a powerful tool that can be used to perform complex operations on data.

Here are some specific examples of how you can use data passing to improve your Swift code:

* **Passing a value to a function:**

func greet(name: String) {
print(“Hello, \(name)!”)
}

greet(“John”)

* **Passing a reference to a value to a function:**

var numbers = [1, 2, 3]

func addOne(toNumbers numbers: [Int]) {
for number in numbers {
number += 1
}
}

addOne(toNumbers: numbers)

print(numbers) // [2, 3, 4]

* **Passing a closure to a function:**

func doSomething(withClosure closure: () -> Void) {
closure()
}

doSomething {
print(“I’m doing something!”)
}

By following these best practices, you can improve the performance and maintainability of your Swift code.

Data passing is a fundamental concept in Swift. By understanding the different types of data passing and the best practices for data passing, you can write more efficient and maintainable code.

How do I pass data back to a previous view controller in Swift?

There are a few ways to pass data back to a previous view controller in Swift. The most common way is to use the `delegate` pattern. In this pattern, the view controller that wants to pass data back sets a delegate property on the view controller that it wants to receive the data. The view controller that receives the data implements the delegate methods to receive the data.

Another way to pass data back to a previous view controller is to use the `unwind segue`. An unwind segue is a segue that is triggered when a user taps the back button in a view controller. When an unwind segue is triggered, the view controller that is being dismissed passes its data to the view controller that is being presented.

Finally, you can also pass data back to a previous view controller by using the `NotificationCenter`. The `NotificationCenter` is a class that allows you to send and receive notifications between different parts of your app. To pass data back to a previous view controller using the `NotificationCenter`, you would create a notification with the data that you want to pass, and then send the notification to the view controller that you want to receive the data.

Here are the steps on how to pass data back to a previous view controller in Swift using the delegate pattern:

1. In the view controller that wants to pass data back, set the delegate property of the view controller that will receive the data.

nextViewController.delegate = self

2. In the view controller that wants to pass data back, implement the delegate methods that will be called when the data is passed back.

func nextViewController(_ nextViewController: NextViewController, didFinishWithData data: Data) {
// Do something with the data
}

3. In the view controller that wants to pass data back, call the `delegate` method to pass the data to the previous view controller.

self.delegate?.nextViewController(self, didFinishWithData: data)

Here are the steps on how to pass data back to a previous view controller in Swift using an unwind segue:

1. In the view controller that wants to pass data back, set the `unwindSegueIdentifier` property to a unique string.

self.unwindSegueIdentifier = “unwindToPreviousViewController”

2. In the view controller that wants to pass data back, implement the `prepare(for segue: UIStoryboardSegue, sender: Any?)` method.

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
// Get the destination view controller for the segue.
let destinationViewController = segue.destination as! PreviousViewController

// Pass the data to the destination view controller.
destinationViewController.data = data
}

3. In the view controller that will receive the data, implement the `viewDidLoad()` method.

override func viewDidLoad() {
// Get the data that was passed from the previous view controller.
let data = segue.destinationViewController as! PreviousViewController.data

// Do something with the data.
}

Here are the steps on how to pass data back to a previous view controller in Swift using the NotificationCenter:

1. Create a notification object with the data that you want to pass.

let notification = Notification(name: Notification.Name(“dataPassedBackNotification”), object: self, userInfo: [“data”: data])

2. Send the notification to the notification center.

NotificationCenter.default.post(notification)

3. In the view controller that will receive the notification, register for the notification.

NotificationCenter.default.addObserver(self, selector: selector(didReceiveDataPassedBackNotification(_:)), name: Notification.Name(“dataPassedBackNotification”), object: nil)

4. Implement the `didReceiveDataPassedBackNotification(_:)` method to receive the notification and do something with the data.

@objc func didReceiveDataPassedBackNotification(_ notification: Notification) {
// Get the data that was passed in the notification.
let data = notification.userInfo![“data”] as! Data

// Do something with the data.
}

In this tutorial, we have discussed how to pass data back to a previous view controller in Swift. We covered two methods: using the segue identifier and using the completion handler. We also discussed the pros and cons of each method.

Overall, the best method for passing data back to a previous view controller depends on the specific needs of your app. If you need to pass a simple data type, such as a string or integer, then using the segue identifier is a quick and easy solution. However, if you need to pass a more complex data type, such as an object or array, then using the completion handler is a more flexible option.

Here are some key takeaways from this tutorial:

  • To pass data back to a previous view controller using the segue identifier, you simply need to set the segue’s identifier property to a unique string value.
  • To pass data back to a previous view controller using the completion handler, you need to create a closure that accepts the data you want to pass back and then call the `dismiss(animated:completion:)` method on the view controller that is presenting the next view controller.
  • The segue identifier method is easier to use, but it is more limited in terms of the data types that you can pass back.
  • The completion handler method is more flexible, but it is more complex to implement.

Ultimately, the best method for passing data back to a previous view controller depends on the specific needs of your app.

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