iOS Interview Questions (UIKit)

UIKit is a framework that was introduced by Apple in 2007 alongside the original iPhone. Today, UIKit remains a crucial part of the iOS development toolkit and is used by developers worldwide. As such, knowledge of UIKit is an essential skill for any iOS developer and is likely to be a topic of discussion in any iOS-related interview.

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• Cracking the iOS Interview
• iOS Interview Questions (Swift)
• iOS Interview Questions (SwiftUI)
• iOS Interview Questions (UIKit) 👇

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To prepare for iOS interview questions related to UIKit, refresh your knowledge and be familiar with following topics:

• UIKit and its components, such as views, view controllers, windows, scenes, events, gestures, animations, transitions, images, colors, text, documents, etc.
• How to use UIKit and Interface Builder to create adaptive layouts that look great on different devices and orientations. You should also know how to use Auto Layout, Size Classes, Constraints, Stack Views, etc. to manage the position and size of your views.
• How to use app delegate methods, scene delegate methods, view controller methods, notification center observers, background modes, weak and strong references, etc. to handle app lifecycle and memory management issues.

1. What is UIKit?

UIKit is a framework that enables you to build user interfaces (UI) for iOS, iPadOS, or tvOS apps. It provides the window and view architecture for implementing your UI, the event-handling infrastructure for delivering Multi-Touch and other types of input to your app, and the main run loop for managing interactions between the user, the system, and your app.

UIKit also includes support for animations, documents, drawing and printing, text management and display, search, app extensions, resource management, and getting information about the current device.

2. What are key components of UIKit?

• Views and controls: These are the basic elements that you use to present your content onscreen and define the interactions allowed with that content. For example, buttons, labels, sliders, switches, text fields, etc.
• View controllers: These are objects that manage views and the structure of your interface. For example, navigation controllers, tab bar controllers, split view controllers, etc.
• Windows and scenes: These are objects that provide the basic container for your app’s views and manage the transitions between different states of your app’s UI.
• Events and gestures: These are objects that deliver Multi-Touch and other types of input to your app and enable custom interactions with your views. For example, taps, swipes, pinches, etc.
• Animations and transitions: These are objects that add motion and visual effects to your views and transitions. For example, UIKit dynamics, view property animators, spring animations, etc.
• Images and colors: These are objects that manage the images, icons, and colors that you use to implement your app’s interface. For example, UIImage, UIColor, SF Symbols, etc.
• Text and fonts: These are objects that manage the display and editing of text in your app. For example, UILabel, UITextView, UIFont, etc.
• Documents and data: These are objects that organize your app’s data and share that data on the pasteboard or with other apps. For example, UIDocument, UIPasteboard, UIActivityViewController, etc.

3. What is the responder chain and how does it handle events?

The responder chain is a series of linked responder objects that handle events in iOS apps. A responder object is any instance of the UIResponder class, such as views, view controllers, or the application object. Events are types of input that occur in your app, such as touch events, press events, shake-motion events, remote-control events, or editing menu messages.

When your app receives an event, UIKit automatically directs that event to the most appropriate responder object, known as the first responder. The first responder varies depending on the type of event. For example, for touch events, the first responder is the view in which the touch occurred; for press events, the first responder is the object that has focus; for editing menu messages, the first responder is the object that you designate.

UIKit manages the responder chain dynamically, using predefined rules to determine which object should be next to receive an event. For example, a view forwards events to its superview, and the root view of a hierarchy forwards events to its view controller.

4. What is UIStackView and how does it layout its subviews?

UIStackView is a control that leverages the power of Auto Layout and Size Classes to manage a stack of subviews, either horizontally or vertically, that dynamically responds to the device’s orientation and screen size.

The order of the subviews in the stack view is determined by their order in the arrangedSubviews array. The exact layout of the subviews depends on the stack view’s distribution, alignment, spacing, and other properties.

You can also fine-tune an arranged view’s appearance by adding additional constraints to the arranged view. For example, you can use constraints to set a minimum or maximum height or width for the view. Or you can define an aspect ratio for the view. Be careful to avoid introducing conflicts when adding constraints to views inside a stack view.

5. How to handle keyboard events in a view controller?

To handle keyboard appearance and disappearance in a view controller, you need to do the following steps:

• Register for keyboard notifications. You can use the NotificationCenter class to observe the UIKeyboardWillShowNotification and UIKeyboardWillHideNotification notifications, which are posted by the system when the keyboard is about to show or hide.
• Adjust your view’s layout when the keyboard shows or hides. In your selector methods, you can use the notification object’s userInfo dictionary to get information about the keyboard’s frame and animation duration. You can use this information to adjust your view’s layout constraints or frame to accommodate the keyboard.
• Unregister for keyboard notifications when the view controller is deallocated. You can use the deinit method of your view controller to remove the observers for the keyboard notifications.