Understanding View Controller Segues and the Presenting View Controller

Introduction

In iOS development, view controllers are the building blocks of user interfaces. When a view controller presents another view controller, it is known as a segue. In this article, we will delve into the world of view controller segues and explore how to determine which view controller segued to another.

Setting up View Controller Segues

Before we dive into the code, let’s quickly discuss the concept of view controller segues. A segue is an instance of UIStoryboardSegue that represents a transition between two view controllers. When a view controller presents another, it creates a new segue instance and sets its properties to indicate which view controller is being presented.

In Xcode, you can set up view controller segues by following these steps:

Select the source view controller in the storyboard or XIB file.
Control-drag from the source view controller to the destination view controller.
Choose the segue type (e.g., modal, push, pop) and click “Add Segue”.
In the attributes inspector, set the presenting view controller property to the desired value.

Understanding the Presenting View Controller Relationship

When a view controller presents another, it establishes a relationship between the two view controllers known as the presenting view controller relationship. This relationship is stored in the presentingViewController property of the presented view controller.

To determine which view controller segued to another, you need to access this presenting view controller relationship. Here’s an example:

let presentingVC = (presentedViewController as? VC1)?.presentingViewController

In this code snippet, we first cast the presentedViewController to a VC1 instance and then access its presentingViewController property.

Querying the Presenting View Controller Relationship

As mentioned earlier, you can query the presenting view controller relationship by accessing the presentingViewController property of the presented view controller. However, there are some nuances to this approach:

If the segue was performed programmatically using performSegue(withIdentifier:sender:), the presenting view controller relationship is not set automatically.
If the segue was performed using a storyboard or XIB file, the presenting view controller relationship is set automatically.

To ensure you get the correct presenting view controller relationship, always check if the segue was performed programmatically or using a storyboard/XIB file:

let presentingVC = (presentedViewController as? VC1)?.presentingViewController

if presentingVC == self {
    // Segue was performed programmatically
} else {
    // Segue was performed using a storyboard/XIB file
}

In this code snippet, we check if the presented view controller is equal to the current view controller (self). If they are equal, it means the segue was performed programmatically.

Let’s consider an example where you have four view controllers: VC1, VC2, VC3, and VC4. Each of these view controllers presents VC4 using a different segue type:

VC1 uses a modal segue to present VC4.
VC2 uses a push segue to present VC4.
VC3 uses a pop segue to present VC4.

To detect which view controller segued to VC4, you can use the following code:

func detectNavigation(fromVC presentingVC: UIViewController?) {
    guard let presentingVC = presentingVC else { return }

    if letsegueIdentifier = presentingVC.presentedViewController?.presentingViewController {
        // Segue was performed using a storyboard/XIB file
        print("Segue from \(presentingVC) to \(segueIdentifier)")
    } else {
        // Segue was performed programmatically
        print("Segue from \(presentingVC) (programmatically)")
    }
}

In this code snippet, we define a function detectNavigation(fromVC:) that takes the presenting view controller as an argument. We use a guard statement to ensure that the presenting view controller is not nil.

We then check if the presented view controller has a presentingViewController property set. If it does, it means the segue was performed using a storyboard/XIB file. Otherwise, we assume the segue was performed programmatically.

By calling this function from each of your view controllers, you can detect which view controller segued to another and respond accordingly.

Conclusion

In conclusion, understanding view controller segues and the presenting view controller relationship is crucial in iOS development. By querying the presentingViewController property of the presented view controller, you can determine which view controller segued to another.

However, there are nuances to this approach, such as checking if the segue was performed programmatically or using a storyboard/XIB file. By following these guidelines and writing code that checks for these conditions, you can ensure accurate results when detecting navigation from multiple view controllers.

Remember to always check your view controller relationships to avoid unexpected behavior in your app. Happy coding!

Last modified on 2023-12-13