UIKit Cheat Sheet

Updated 2026-05-25

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UIKit is Apple's foundational framework for building user interfaces in iOS, iPadOS, tvOS, and watchOS applications. It provides the window and view architecture needed to display content on screen, the infrastructure to handle user interactions through touch and gestures, and the tools to manage your app's data and content flow. Understanding UIKit is essential even in the SwiftUI era — many production apps combine both frameworks, and iOS 26 deepened that integration further with automatic @Observable tracking in layout methods and a new updateProperties() lifecycle phase. UIKit's view controller lifecycle, Auto Layout system, compositional collection views, and diffable data sources remain the standard for complex, high-performance interfaces.

What This Cheat Sheet Covers

This topic spans 33 focused tables and 296 indexed concepts, 185 flashcards. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.

Table 1: View Hierarchy and Core View ClassesTable 2: UIViewController LifecycleTable 3: Auto Layout — Constraint CreationTable 4: Auto Layout — Properties and GuidesTable 5: UITableView BasicsTable 6: UITableViewCell ConfigurationTable 7: UICollectionView LayoutsTable 8: Diffable Data SourcesTable 9: UINavigationControllerTable 10: View Controller Presentation and Modal StylesTable 11: UITabBarControllerTable 12: Gesture Recognizers — Basic GesturesTable 13: Gesture Recognizer PropertiesTable 14: UIView Animation — Basic MethodsTable 15: Animation Properties and OptionsTable 16: UIViewPropertyAnimatorTable 17: View Controller TransitionsTable 18: Common UI ControlsTable 19: Context Menus and ActionsTable 20: Text Input ControlsTable 21: UIScrollViewTable 22: CALayer BasicsTable 23: Drawing and Custom ShapesTable 24: Layout Update MethodsTable 25: UIFont and Dynamic TypeTable 26: Size Classes and Trait CollectionsTable 27: UIAppearance and StylingTable 28: Responder ChainTable 29: View Controller ContainmentTable 30: Alert Controllers and Action SheetsTable 31: Additional View ControllersTable 32: Additional UI ComponentsTable 33: UIWindow and Scenes

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Table 1: View Hierarchy and Core View Classes

The UIView is the atomic unit of every UIKit interface; every visible element is a subview sitting inside a tree rooted at a UIWindow. Understanding how views are added, layered, and positioned in this hierarchy is the prerequisite for everything else in UIKit.

Class	Example	Description
UIView	`let view = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))` `view.backgroundColor = .red`	• The fundamental building block for all visual elements • manages a rectangular area on screen and handles drawing and touch events
addSubview	`parentView.addSubview(childView)`	• Adds a view as a subview to another view's hierarchy • child appears on top of the parent
removeFromSuperview	`childView.removeFromSuperview()`	• Removes a view from its parent's subview hierarchy • automatically releases strong references
UILabel	`let label = UILabel()` `label.text = "Hello"`	• Displays one or more lines of read-only text • supports attributed strings and custom fonts
UIImageView	`let imageView = UIImageView(image: UIImage(named: "photo"))`	Displays a single image or animates a sequence of images
UIStackView	`let stack = UIStackView(arrangedSubviews: [view1, view2])` `stack.axis = .vertical`	• Arranges views in horizontal or vertical layouts without manual constraints • automatically manages spacing and alignment
frame	`view.frame = CGRect(x: 50, y: 100, width: 200, height: 150)`	• Position and size in the parent's coordinate system • avoid setting when using Auto Layout
bounds	`let size = view.bounds.size`	• Position and size in the view's own coordinate system • origin typically `(0, 0)`
center	`view.center = CGPoint(x: 150, y: 200)`	The center point of the view in its parent's coordinate system
transform	`view.transform = CGAffineTransform(rotationAngle: .pi / 4)`	• Affine transformation for rotation, scaling, or translation • applied relative to center point
subviews	`let children = parentView.subviews`	Read-only array of all direct child views in the order they were added
superview	`if let parent = view.superview { }`	• Reference to the immediate parent view • `nil` if the view has no parent
bringSubviewToFront	`parentView.bringSubviewToFront(childView)`	Moves a subview to the top of the draw order so it renders on top of siblings
sendSubviewToBack	`parentView.sendSubviewToBack(backgroundView)`	Moves a subview behind all other sibling views in the draw order
insertSubview at index	`parentView.insertSubview(newView, at: 1)`	Inserts a subview at a specific position in the subviews array, controlling z-order

Table 2: UIViewController Lifecycle

The view controller lifecycle defines a precise sequence of callbacks between load, appearance, and disappearance; calling super at the right time in each override is mandatory. iOS 26 added updateProperties() — a dedicated phase for syncing model data to view properties independently of layout work.

Method	Example	Description
viewDidLoad	`override func viewDidLoad() {` `super.viewDidLoad()` `setupUI()` `}`	• Called once after the view is loaded into memory • ideal for one-time setup like configuring subviews

The rest of this section is part of the full cheat sheet

Table 3: Auto Layout — Constraint Creation

Auto Layout calculates view frames by solving a system of linear constraints at runtime. Always use Layout Anchors for new code — they are type-safe and far more readable than the original NSLayoutConstraint API.

Technique	Example	Description
Layout Anchors	`view.leadingAnchor.constraint(equalTo: parent.leadingAnchor, constant: 16)`	• Type-safe constraint creation using anchor properties • cleaner syntax than raw `NSLayoutConstraint`

The rest of this section is part of the full cheat sheet

Table 4: Auto Layout — Properties and Guides

Layout guides and content-sizing priorities let Auto Layout work with semantic regions (safe area, margins, readable content) and allow views to express their natural size preferences without requiring explicit dimension constraints.

Property	Example	Description
safeAreaLayoutGuide	`view.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor)`	• Layout guide representing the area not covered by navigation bars, tab bars, or notch • critical for modern iPhone layouts

The rest of this section is part of the full cheat sheet

Table 1: View Hierarchy and Core View Classes

Class	Example	Description
UIView	`let view = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))` `view.backgroundColor = .red`	• The fundamental building block for all visual elements • manages a rectangular area on screen and handles drawing and touch events
addSubview	`parentView.addSubview(childView)`	• Adds a view as a subview to another view's hierarchy • child appears on top of the parent
removeFromSuperview	`childView.removeFromSuperview()`	• Removes a view from its parent's subview hierarchy • automatically releases strong references
UILabel	`let label = UILabel()` `label.text = "Hello"`	• Displays one or more lines of read-only text • supports attributed strings and custom fonts
UIImageView	`let imageView = UIImageView(image: UIImage(named: "photo"))`	Displays a single image or animates a sequence of images
UIStackView	`let stack = UIStackView(arrangedSubviews: [view1, view2])` `stack.axis = .vertical`	• Arranges views in horizontal or vertical layouts without manual constraints • automatically manages spacing and alignment
frame	`view.frame = CGRect(x: 50, y: 100, width: 200, height: 150)`	• Position and size in the parent's coordinate system • avoid setting when using Auto Layout
bounds	`let size = view.bounds.size`	• Position and size in the view's own coordinate system • origin typically `(0, 0)`
center	`view.center = CGPoint(x: 150, y: 200)`	The center point of the view in its parent's coordinate system
transform	`view.transform = CGAffineTransform(rotationAngle: .pi / 4)`	• Affine transformation for rotation, scaling, or translation • applied relative to center point
subviews	`let children = parentView.subviews`	Read-only array of all direct child views in the order they were added
superview	`if let parent = view.superview { }`	• Reference to the immediate parent view • `nil` if the view has no parent
bringSubviewToFront	`parentView.bringSubviewToFront(childView)`	Moves a subview to the top of the draw order so it renders on top of siblings
sendSubviewToBack	`parentView.sendSubviewToBack(backgroundView)`	Moves a subview behind all other sibling views in the draw order
insertSubview at index	`parentView.insertSubview(newView, at: 1)`	Inserts a subview at a specific position in the subviews array, controlling z-order

Table 2: UIViewController Lifecycle

Method	Example	Description
viewDidLoad	`override func viewDidLoad() {` `super.viewDidLoad()` `setupUI()` `}`	• Called once after the view is loaded into memory • ideal for one-time setup like configuring subviews

Table 3: Auto Layout — Constraint Creation

Technique	Example	Description
Layout Anchors	`view.leadingAnchor.constraint(equalTo: parent.leadingAnchor, constant: 16)`	• Type-safe constraint creation using anchor properties • cleaner syntax than raw `NSLayoutConstraint`

Table 4: Auto Layout — Properties and Guides

Property	Example	Description
safeAreaLayoutGuide	`view.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor)`	• Layout guide representing the area not covered by navigation bars, tab bars, or notch • critical for modern iPhone layouts