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airbnb/epoxy-ios
Epoxy is a suite of declarative UI APIs for building UIKit applications in Swift
.package(url: "https://github.com/airbnb/epoxy-ios.git", from: "0.3.0")
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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.

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Table of contents

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:

  1. In Xcode, select “File” → “Swift Packages” → “Add Package Dependency”
  2. 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
EpoxyCore Foundational APIs that are used to build all Epoxy declarative UI APIs

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
      }
  })
Screenshot

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
      }
  }
}
Screenshot

You can learn more about EpoxyCollectionView in its wiki entry.

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
      }))
  }
}
Screenshot

You can learn more about EpoxyBars in its wiki entry.

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
        })
    }
  }
}
Screenshot

You can learn more about EpoxyNavigationController in its wiki entry.

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
        })
    }
  }
}
Screenshot

You can learn more about EpoxyPresentations in its wiki entry.

Documentation and Tutorials

For full documentation and step-by-step tutorials please check the wiki.

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.

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.

License

Epoxy is released under the Apache License 2.0. See LICENSE for details.

Credits

Logo design by Alana Hanada and Jonard La Rosa

GitHub

link
Stars: 538
Last commit: 4 days ago

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iOS Software Engineer @ Perry Street Software
Perry Street Software is Jack’d and SCRUFF. We are two of the world’s largest gay, bi, trans and queer social dating apps on iOS and Android. Our brands reach more than 20 million members worldwide so members can connect, meet and express themselves on a platform that prioritizes privacy and security. We invest heavily into SwiftUI and using Swift Packages to modularize the codebase.

Dependencies

Release Notes

0.3.0
3 weeks ago

Added

  • Added support for Array and Optional expressions to model result builders
  • Added support for Optional expressions to PresentationModel result builders
  • Made AnyItemModel and AnySupplementaryItemModel conform to DidChangeStateProviding, DidChangeStateProviding and SetBehaviorsProviding
  • Made AnyItemModel, AnySupplementaryItemModel, and AnyBarModel conform to StyleIDProviding
  • Adds a keyboardContentInsetAdjustment property to UIScrollView with the amount that the that its contentInset.bottom has been adjusted to accommodate for the keyboard by a KeyboardPositionWatcher
  • Made ItemSelectionStyle conform to Hashable
  • ReuseIDStore has a new method to vend a previously registered reuse ID, registeredReuseID(for:)

Fixed

  • Bar installers gracefully handle redundant calls to install/uninstall
  • CollectionView more gracefully handles styleID mutations after registration

Changed

  • ReuseIDStore.registerReuseID(for:) has been renamed to ReuseIDStore.reuseID(byRegistering:)

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