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Learn how to pass data between view controllers in Swift using delegation, ensuring a smooth user experience when returning to the previous screen.
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How to Successfully Transit Data between ViewControllers in Swift

In the world of iOS app development, managing the navigation and data flow between different screens or view controllers (VCs) is crucial for building an intuitive user experience. One common scenario is needing to pass data back to a previous view controller when navigating back from another. In this guide, we will explore how to achieve this using Swift through delegation, all while breaking it down into clear, manageable steps.

The Problem

Suppose you have a ViewController that contains a label and a button to transition to a secondVC. The secondVC has a text field, a label, and a button. The requirement is that when the user presses the back button of the navigation bar after entering text, the label text on secondVC should be transferred to the label in ViewController. Although you might initially consider using a segue for this, it’s important to understand that segues are primarily for navigation, not for passing back data.

Let’s break down the solution into practical steps.

The Solution: Using Delegation

What is Delegation?

Delegation is a design pattern that allows one object to send messages to another object when a specific event occurs. In our case, we'll use it to send the text from secondVC back to ViewController. This approach keeps your view controllers loosely coupled and makes your code more manageable.

Step-by-Step Implementation

Here’s how we can implement this solution.

1. Create a Delegate Protocol

First, you need to create a delegate protocol in secondVC. This protocol will define the method that ViewController must implement to receive the text from secondVC.

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2. Implement the Delegate in ViewController

Next, let’s implement this protocol in ViewController. We'll create a method to receive the data and update nameLabel accordingly.

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3. Set the Delegate in secondVC

Now, let’s modify secondVC to define a weak delegate property and invoke the delegate method when the save button is clicked.

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Summary of Code Changes

Create a delegate protocol in secondVC to facilitate data transfer.

Implement the delegate protocol in ViewController to handle the incoming data.

Set the delegate property in ViewController when transitioning to secondVC.

Invoke the delegate method in secondVC to pass back the data and dismiss the view controller.

Conclusion

By using the delegation pattern, you've now successfully enabled secondVC to pass data back to ViewController. This method is not only efficient but also sets a solid grounding for scaling your app as it grows. Mastering data transit between view controllers enhances your overall iOS development skills, making it easier to build complex applications while maintaining clean and readable code.

Feel free to experiment with other methods for data passing, but delegation is one of the most robust approaches for handling these scenarios in Swift. Happy coding!