Stagehand provides a modern, type-safe API for building animations on iOS. Stagehand is designed around a set of core ideas:
- Composition of Structures - Stagehand makes it easy to build complex, multi-part animations that are built from small, reusable pieces that are easier to reason about.
- Separation of Construction and Execution - Stagehand provides separate mechanisms for the construction and execution, which increases the flexibility of animations and makes concepts like queuing a series of animations work straight out of the box.
- Compile-Time Safety - Stagehand uses modern Swift features to provide a compile-time safe API for defining animations.
- Testability - Stagehand builds on the concept of snapshot testing to introduce a visual testing paradigm for animations.
To install Stagehand via CocoaPods, simply add the following line to your
To install StagehandTesting, the animation snapshot testing utilities, add the following line to your test target definition in your
By default, this will use Point-Free's SnapshotTesting to record snapshots and perform comparisons. To instead use Uber's iOSSnapshotTestCase as the snapshotting engine, set your test target dependency to use the
Swift Package Manager
To install Stagehand via Swift Package Manager, add the following to your
dependencies: [ .package(url: "https://github.com/cashapp/stagehand", from: "4.0.0"), ],
Getting Started with Stagehand
An animation begins with the construction of an
Animation is generic over a type of element and acts as a definition of how that element should be animated.
As an example, we can write an animation that highlights a view by fading its alpha to 0.8 and back:
var highlightAnimation = Animation<UIView>() highlightAnimation.addKeyframe(for: \.alpha, at: 0, value: 1) highlightAnimation.addKeyframe(for: \.alpha, at: 0.5, value: 0.8) highlightAnimation.addKeyframe(for: \.alpha, at: 1, value: 1)
Let's say we've defined a view, which we'll call
BinaryView, that has two subviews,
rightView, and we want to highlight each of the subviews in sequence. We can define an animation for our
BinaryView with two child animations:
var binaryAnimation = Animation<BinaryView>() binaryAnimation.addChild(highlightAnimation, for: \.leftView, startingAt: 0, relativeDuration: 0.5) binaryAnimation.addChild(highlightAnimation, for: \.rightView, startingAt: 0.5, relativeDuration: 0.5)
Once we've set up our view and we're ready to execute our animation, we can call the
perform method to start animating:
let view = BinaryView() // ... binaryAnimation.perform(on: view)
Running the Demo App
Stagehand ships with a demo app that shows examples of many of the features provided by Stagehand. To run the demo app, open the
Example directory and run:
bundle install bundle exec pod install open Stagehand.xcworkspace
From here, you can run the demo app and see a variety of examples for how to use the framework. In that workspace, there is also a playground that includes documentation and tutorials for how each feature works.
We’re glad you’re interested in Stagehand, and we’d love to see where you take it. Please read our contributing guidelines prior to submitting a Pull Request.
Copyright 2020 Square, Inc. Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.