dnrops/epoxy-ios

Epoxy is a suite of declarative UI APIs for building UIKit applications in Swift. Epoxy is inspired and influenced by the wonderful Epoxy framework on Android, as well as other declarative UI frameworks in Swift such as SwiftUI.

Epoxy was developed at Airbnb and powers thousands of screens in apps that are shipped to millions of users. It has been developed and refined for years by dozens of contributors.

Below are a few sample screens from the Airbnb app that we’ve built using Epoxy. Our usages of Epoxy span from our simplest forms and static screens to our most advanced and dynamic features. | Home Details | Home Photos | Messaging | Registration | | — | — | — | — | | | | | |

Installation
- CocoaPods
- Swift Package Manager (SPM)
Modules
Documentation and tutorials
Getting started
FAQ
Contributing
License
Credits

Installation

Epoxy can be installed using CocoaPods or Swift Package Manager.

CocoaPods

To get started with Epoxy using Cocoapods add the following to your Podfile and then follow the integration instructions.

pod 'Epoxy'

Epoxy is separated into podspecs for each module so you only have to include what you need.

Swift Package Manager (SPM)

To install Epoxy using Swift Package Manager you can follow the tutorial published by Apple using the URL for the Epoxy repo with the current version:

In Xcode, select “File” → “Swift Packages” → “Add Package Dependency”
Enter https://github.com/airbnb/epoxy-ios.git

Epoxy is separated library products for each module so you only have to include what you need.

Modules

Epoxy has a modular architecture so you only have to include what you need for your use case:

Module	Description
`Epoxy`	Includes all of the below modules in a single import statement
`EpoxyCollectionView`	Declarative API for driving the content of a `UICollectionView`
`EpoxyNavigationController`	Declarative API for driving the navigation stack of a `UINavigationController`
`EpoxyPresentations`	Declarative API for driving the modal presentations of a `UIViewController`
`EpoxyBars`	Declarative API for adding fixed top/bottom bar stacks to a `UIViewController`
`EpoxyLayoutGroups`	Declarative API for building composable layouts in UIKit with a syntax similar to SwiftUI’s stack APIs
`EpoxyCore`	Foundational APIs that are used to build all Epoxy declarative UI APIs

Documentation and tutorials

For full documentation and step-by-step tutorials please check the wiki. For type-level documentation, see the Epoxy DocC documentation hosted on the Swift Package Index.

There’s also a full sample app with a lot of examples that you can either run via the EpoxyExample scheme in Epoxy.xcworkspace or browse its source.

If you still have questions, feel free to create a new issue.

Getting started

EpoxyCollectionView

EpoxyCollectionView provides a declarative API for driving the content of a UICollectionView. CollectionViewController is a subclassable UIViewController that lets you easily spin up a UICollectionView-backed view controller with a declarative API.

The following code samples will render a single cell in a UICollectionView with a TextRow component rendered in that cell. TextRow is a simple UIView containing two labels that conforms to the EpoxyableView protocol.

You can either instantiate a CollectionViewController instance directly with sections, e.g. this view controller with a selectable row:

Source Result

enum DataID {
  case row
}

let viewController = CollectionViewController(
  layout: UICollectionViewCompositionalLayout
    .list(using: .init(appearance: .plain)),
  items: {
    TextRow.itemModel(
      dataID: DataID.row,
      content: .init(title: "Tap me!"),
      style: .small)
      .didSelect { _ in
        // Handle selection
      }
  })

Or you can subclass CollectionViewController for more advanced scenarios, e.g. this view controller that keeps track of a running count:

Source Result

class CounterViewController: CollectionViewController {
  init() {
    let layout = UICollectionViewCompositionalLayout
      .list(using: .init(appearance: .plain))
    super.init(layout: layout)
    setItems(items, animated: false)
  }

  enum DataID {
    case row
  }

  var count = 0 {
    didSet {
      setItems(items, animated: true)
    }
  }

  @ItemModelBuilder
  var items: [ItemModeling] {
    TextRow.itemModel(
      dataID: DataID.row,
      content: .init(
        title: "Count \(count)",
        body: "Tap to increment"),
      style: .large)
      .didSelect { [weak self] _ in
        self?.count += 1
      }
  }
}

You can learn more about EpoxyCollectionView in its wiki entry, or by browsing the code documentation.

EpoxyBars

EpoxyBars provides a declarative API for rendering fixed top, fixed bottom, or input accessory bar stacks in a UIViewController.

The following code example will render a ButtonRow component fixed to the bottom of the UIViewController‘s view. ButtonRow is a simple UIView component that contains a single UIButton constrained to the margins of the superview that conforms to the EpoxyableView protocol:

Source Result

class BottomButtonViewController: UIViewController {
  override func viewDidLoad() {
    super.viewDidLoad()
    bottomBarInstaller.install()
  }

  lazy var bottomBarInstaller = BottomBarInstaller(
    viewController: self,
    bars: bars)

  @BarModelBuilder
  var bars: [BarModeling] {
    ButtonRow.barModel(
      content: .init(text: "Click me!"),
      behaviors: .init(didTap: {
        // Handle button selection
      }))
  }
}

You can learn more about EpoxyBars in its wiki entry, or by browsing the code documentation.

EpoxyNavigationController

EpoxyNavigationController provides a declarative API for driving the navigation stack of a UINavigationController.

The following code example shows how you can use this to easily drive a feature that has a flow of multiple view controllers:

Source Result

class FormNavigationController: NavigationController {
  init() {
    super.init()
    setStack(stack, animated: false)
  }

  enum DataID {
    case step1, step2
  }

  var showStep2 = false {
    didSet {
      setStack(stack, animated: true)
    }
  }

  @NavigationModelBuilder
  var stack: [NavigationModel] {
    .root(dataID: DataID.step1) { [weak self] in
      Step1ViewController(didTapNext: {
        self?.showStep2 = true
      })
    }

    if showStep2 {
      NavigationModel(
        dataID: DataID.step2,
        makeViewController: {
          Step2ViewController(didTapNext: {
            // Navigate away from this step.
          })
        },
        remove: { [weak self] in
          self?.showStep2 = false
        })
    }
  }
}

You can learn more about EpoxyNavigationController in its wiki entry, or by browsing the code documentation.

EpoxyPresentations

EpoxyPresentations provides a declarative API for driving the modal presentation of a UIViewController.

The following code example shows how you can use this to easily drive a feature that shows a modal when it first appears:

Source Result

class PresentationViewController: UIViewController {
  override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    setPresentation(presentation, animated: true)
  }

  enum DataID {
    case detail
  }

  var showDetail = true {
    didSet {
      setPresentation(presentation, animated: true)
    }
  }

  @PresentationModelBuilder
  var presentation: PresentationModel? {
    if showDetail {
      PresentationModel(
        dataID: DataID.detail,
        presentation: .system,
        makeViewController: { [weak self] in
          DetailViewController(didTapDismiss: {
            self?.showDetail = false
          })
        },
        dismiss: { [weak self] in
          self?.showDetail = false
        })
    }
  }
}

You can learn more about EpoxyPresentations in its wiki entry, or by browsing the code documentation.

EpoxyLayoutGroups

LayoutGroups are UIKit Auto Layout containers inspired by SwiftUI’s HStack and VStack that allow you to easily compose UIKit elements into horizontal and vertical groups.

VGroup allows you to group components together vertically to create stacked components like this:

Source Result

// Set of dataIDs to have consistent
// and unique IDs
enum DataID {
  case title
  case subtitle
  case action
}

// Groups are created declaratively
// just like Epoxy ItemModels
let group = VGroup(
  alignment: .leading,
  spacing: 8)
{
  Label.groupItem(
    dataID: DataID.title,
    content: "Title text",
    style: .title)
  Label.groupItem(
    dataID: DataID.subtitle,
    content: "Subtitle text",
    style: .subtitle)
  Button.groupItem(
    dataID: DataID.action,
    content: "Perform action",
    behaviors: .init { button in
      print("Button tapped! \(button)")
    },
    style: .standard)
}

// install your group in a view
group.install(in: view)

// constrain the group like you
// would a normal subview
group.constrainToMargins()

As you can see, this is incredibly similar to the other APIs used in Epoxy. One important thing to note is that install(in: view) call at the bottom. Both HGroup and VGroup are written using UILayoutGuide which prevents having large nested view hierarchies. To account for this, we’ve added this install method to prevent the user from having to add subviews and the layout guide manually.

Using HGroup is almost exactly the same as VGroup but the components are now horizontally laid out instead of vertically:

Source Result

enum DataID {
  case icon
  case title
}

let group = HGroup(spacing: 8) {
  ImageView.groupItem(
    dataID: DataID.icon,
    content: UIImage(systemName: "person.fill")!,
    style: .init(size: .init(width: 24, height: 24)))
  Label.groupItem(
    dataID: DataID.title,
    content: "This is an IconRow")
}

group.install(in: view)
group.constrainToMargins()

Groups support nesting too, so you can easily create complex layouts with multiple groups:

Source Result

enum DataID {
  case checkbox
  case titleSubtitleGroup
  case title
  case subtitle
}

HGroup(spacing: 8) {
  Checkbox.groupItem(
    dataID: DataID.checkbox,
    content: .init(isChecked: true),
    style: .standard)
  VGroupItem(
    dataID: DataID.titleSubtitleGroup,
    style: .init(spacing: 4))
  {
    Label.groupItem(
      dataID: DataID.title,
      content: "Build iOS App",
      style: .title)
    Label.groupItem(
      dataID: DataID.subtitle,
      content: "Use EpoxyLayoutGroups",
      style: .subtitle)
  }
}

You can learn more about EpoxyLayoutGroups in its wiki entry, or by browsing the code documentation.

FAQ

Contributing

Pull requests are welcome! We’d love help improving this library. Feel free to browse through open issues to look for things that need work. If you have a feature request or bug, please open a new issue so we can track it. Contributors are expected to follow the Code of Conduct.