UIKit Reference

Kip Landergren

(Updated: )

My cheat sheet for UIKit covering terminology, configuration tips for objects like UIViewController, UILabel, and UIButton, and helpful links.

Contents

Design

Dimensions

Devices
iPhone SE 1334px x 750px

UIKit Terminology

Anchor
a factory class for creating layout constraints from view attributes
Baseline
line at bottom of text
Layout Constraint
an equation that defines how a view attribute should exist, often in relationship to another view attribute
Leading Edge
the first edge encountered when scanning in reading order (locale-dependent; changes with right-to-left or left-to-right languages)
Trailing Edge
the last edge encountered when scanning in reading order (locale-dependent; changes with right-to-left or left-to-right languages)
View Attribute
part of the object’s visual representation, typically corresponding to an edge or dimension, that should be used to get the value for the layout constraint

UIViewController

Properties

Prefer lazy loading when the property represents a simple element of the view controller’s view hierarchy:

private lazy var _closeButton: UIBarButtonItem = {
  UIBarButtonItem(title: "Close", style: .plain,
           target: self, action: #selector(t_closePressed(_:)))
}()

For more complex view configuration, consider refactoring.

Prefer implicitly unwrapped optionals when the property is nil after initialization but known to be with value before use, and if nil upon use would be an error:

private var _modalViewController: MyModalViewController!

Prefer optionals for any publically accessible properties, like delegates:

var editingDelegate: EditingDelegate?

Prefer normal types for non-optional values passed or created during initialization:

private var _name = "Editor"

Subclassing

Initialization

Create any required data structures to put view controller into a known good state.

Specifying a convenience initializer, noting the call to self.init:

convenience init() {
  self.init(nibName: nil, bundle: nil)
  title = NSLocalizedString("title", comment: "title")
  // set up any navigationItem properties here, not in loadView()
}

Specifying a custom initializer, noting:

init(arg: String) {
  // set up any internal state
  _arg = arg
  super.init(nibName: nil, bundle: nil)
  title = NSLocalizedString("title", comment: "title")
  // set up any navigationItem properties here, not in loadView()
}
@available(*, unavailable)
required init?(coder: NSCoder) {
  fatalError("init(coder:) has not been implemented")
}

loadView()

Create and wire together your view hierarchy, ensuring the root view is assigned to .view. Do not call super.

viewDidLoad()

View hierarchy exists in a valid state. Load any data necessary for display, and add any initial constraints.

Adding a Child View Controller

addChild(viewController)
view.addSubview(viewController.view)
viewController.didMove(toParent: self)

UINavigationController

Generally: do not set translatesAutoresizingMaskIntoConstraints to false on views being embedded in a UINavigationController.

When presenting modally from a navigation controller, the presented view controller is not embedded in the navigation controller doing the presenting. Therefore if you wish to have navigability in the modal, embed the view controller in a separate navigation controller before presenting.

UITableViewController

Generally: a UITableViewController should take up the whole screen. If a view controller needs the functionality of a UITableView, create a custom UIViewController to address.

Styles

UITableView

Quick facts:

From the docs:

The table view’s delegate in tableView(_:cellForRowAt:) should always reset all content when reusing a cell.

UINavigationItem

Object containing the views and buttons for display in the navigation bar.

Uses:

Notes:

UIStackView

UIStackView is nonrendering, meaning it provides no user interface of its own. This means settings like backgroundColor have no effect.

UILabel

A UILabel’s default backgroundColor is transparent.

System-provided .textColor values include:

Font

label.font = UIFont.preferredFont(forTextStyle: .headline)
label.adjustsFontForContentSizeCategory = true
label.adjustsFontSizeToFitWidth = true
label.allowsDefaultTighteningForTruncation = true
label.baselineAdjustment = .alignCenters

Accessibility

label.accessibilityIdentifier = "Unique Article Title"

UIButton

UIButton Creation

_button = UIButton(type: .custom)

UIButton.ButtonType Values
custom
system
detailDisclosure
infoLight
infoDark
contactAdd
roundedRect

UIBarButtonItem
isEnabled enables or disables the state of the button

Anchors

A full list is within the enum NSLayoutConstraint.Attribute.

X Axis
leadingAnchor a view’s leading edge. should be preferred especially for RTL and LTR localization.
trailingAnchor a view’s trailing edge. should be preferred especially for RTL and LTR localization.
leftAnchor a view’s left edge
rightAnchor a view’s right edge
centerXAnchor a view’s horizontal center

Y Axis
topAnchor a view’s top edge
bottomAnchor a views bottom edge
firstBaselineAnchor baseline of first line of a view containing multiple lines of text
lastBaselineAnchor baseline of last line of a view containing multiple lines of text
centerYAnchor

Dimensional
widthAnchor a view’s width
heightAnchor a view’s height

Resources

Apple Developer Documentation

Note: I have found that the built-in Xcode documentation for UIKit is not as up-to-date as what is available on developer.apple.com.

Related Documents