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https://github.com/dfed/relativity
A programmatic layout engine and DSL that provides an alternative to Auto Layout
https://github.com/dfed/relativity
Last synced: about 2 months ago
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A programmatic layout engine and DSL that provides an alternative to Auto Layout
- Host: GitHub
- URL: https://github.com/dfed/relativity
- Owner: dfed
- License: apache-2.0
- Created: 2016-12-27T03:01:03.000Z (almost 8 years ago)
- Default Branch: main
- Last Pushed: 2024-10-28T18:39:37.000Z (about 2 months ago)
- Last Synced: 2024-10-31T22:42:17.837Z (about 2 months ago)
- Language: Swift
- Homepage:
- Size: 146 KB
- Stars: 23
- Watchers: 5
- Forks: 4
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
- Contributing: Contributing.md
- License: LICENSE
Awesome Lists containing this project
README
# Relativity
[](https://github.com/dfed/Relativity/actions?query=workflow%3ACI+branch%3Amain)
[](https://github.com/Carthage/Carthage/)
[](https://cocoapods.org/pods/Relativity)
[](https://cocoapods.org/pods/Relativity)
[](https://cocoapods.org/pods/Relativity)
Relativity provides a DSL for programmatic layout that makes it easy to achieve pixel-perfect spacing and alignment.
# Deprecated
This library is deprecated in favor of [Block’s Paralayout library](https://github.com/square/Paralayout). Paralayout solves the same set of prolems that Relativity does, and has been actively maintained for longer than Relativity.
## Programmatic Layout
There are four basic steps to laying out views programmatically.
1. **Create views**. Do this in `init` or `viewDidLoad`.
2. **Create view hierarchy** with `addSubview()`. Do this in `init` or `viewDidLoad`.
3. **Size views**. Do this in `layoutSubviews`.
4. **Position views**. Do this in `layoutSubviews`.
### Positioning Views
Each view has nine anchors that are used for alignment.
topLefttoptopRight
leftmiddleright
bottomLeftbottombottomRight
Positioning views is done by aligning the desired anchor on a view to another view’s anchor, plus an offset. A `-->` moves the view on the left side to the position described on the right side. A `<--` moves the view on the right side to the position described on the left side. You can also explicitly align views using the `align(to:xOffset:yOffset)` method in [ViewPosition.swift](Sources/ViewPosition.swift#L105).
#### Examples
To align view `a` to be 10 points to the left of view `b`:
```swift
a.right --> 10.horizontalOffset + b.left
```
To align view `a` to be 10 points to the right of view `b`:
```swift
b.right + 10.horizontalOffset <-- a.left
```
To align view `a` to be 10 points below its superview’s top center:
```swift
a.top --> 10.verticalOffset + .top
```
For more examples, check out the [ViewPositionVisualization](RelativityVisualization.playground/Pages/ViewPositionVisualization.xcplaygroundpage/Contents.swift) playground page.
#### UILabels
Relativity makes it easy to position your `UILabel`s using the font’s [cap height](https://en.wikipedia.org/wiki/Cap_height) and [baseline](https://en.wikipedia.org/wiki/Baseline_(typography)) by adding six anchors specifically for labels.
capLeftcapcapRight
baselineLeftbaselinebaselineRight
If your spec says that the top of your `underlineView` should align with the baseline of label `a`, all you need is:
```swift
underlineView.top --> a.baseline
```
For a visual example, check out the [FontMetricsVisualization](RelativityVisualization.playground/Pages/FontMetricsVisualization.xcplaygroundpage/Contents.swift) playground page.
### Flexible distribution of subviews
Since views need to be laid out flexibly over various iOS device sizes, Relativity has the ability to easily distribute subviews with flexible positioning along an axis.
Subview distribution can be controlled by positioning fixed and flexible spacers in between views. Fixed spaces represent points on screen. Fixed spaces are created by inserting `CGFloatConvertible` (`Int`, `Float`, `CGFloat`, or `Double`) types into the distribution expression, or by initializing a `.fixed(CGFloatConvertible)` enum case directly. Flexible spacers represent proportions of the remaining space in the superview after the subviews and fixed spacers have been accounted for. You can create flexible spacers by surrounding an `Int` with a spring `~` operator, or by initializing the `.flexible(Int)` enum case directly. A `~2~` represents twice the space that `~1~` does. Views, fixed spacers, and flexible spacers are bound together by a bidirectional anchor `<>` operator, or via a operatorless result builder.
#### Examples
To equally distribute subviews `a`, `b`, and `c` at equal distances along a horizontal axis:
```swift
superview.distributeSubviewsHorizontally() {
a <> ~1~ <> b <> ~1~ <> c
}
```
To make the space between `a` and `b` twice as large as the space between `b` and `c`:
```swift
superview.distributeSubviewsHorizontally() {
a <> ~2~ <> b <> ~1~ <> c
}
```
To pin `a` to be 8pts from the left side, and distribute `b` and `c` with equal spacing over the remaining space:
```swift
superview.distributeSubviewsHorizontally() {
8 <> a <> ~1~ <> b <> ~1~ <> c
}
```
To equally distribute subviews `a`, `b`, and `c` at equal distances along a vertical axis, but align the subviews within the left half of `superview`:
```swift
superview.distributeSubviewsVertically(within: CGRect(x: 0.0, y: 0.0, width: superview.bounds.midX, height: superview.bounds.height)) {
a
~1~
b
~1~
c
}
```
For a visual example, check out the [ViewPositionVisualization](RelativityVisualization.playground/Pages/ViewPositionVisualization.xcplaygroundpage/Contents.swift) playground page.
### Pixel Rounding
Relativity ensures that you never align a frame to a non-integral pixel, so no need to worry about blurry UI! I’ve also vended a public [PixelRounder](Sources/PixelRounder.swift) for those who want to use it for frame sizing.
### Sizing Views
Relativity makes it easy to size views based on the space between previously laid-out content. Use the `|--|` operator to determine the size between view anchors.
#### Examples
To size view `b` to fit between views `a` and `c`:
```swift
b.bounds.size = a.topRight |--| c.bottomLeft
```
To size view `b` to fit between views `a` and `c` with a 16 point horizontal inset:
```swift
b.bounds.size = a.topRight |--| c.bottomLeft + -16.horizontalOffset
```
To size view `b` to be the same height as view `a`, and fit between `a` and the right side of `a`'s superview:
```swift
b.bounds.size = CGSize(width: (a.right |--| .right).width, height: a.bounds.height)
```
## Requirements
* Xcode 15.0 or later.
* iOS 13 or later.
* Swift 5.9 or later.
## Installation
### Swift Package Manager
To install Relativity in your iOS project with [Swift Package Manager](https://github.com/apple/swift-package-manager), the following lines can be added to your `Package.swift` file:
```swift
dependencies: [
.package(url: "https://github.com/dfed/Relativity", from: "3.0.0"),
]
```
### CocoaPods
To install Relativity in your iOS project with [CocoaPods](http://cocoapods.org), add the following to your `Podfile`:
```
platform :ios, '12.0'
pod 'Relativity', '~> 3.0'
```
### Submodules
To use git submodules, checkout the submodule with `git submodule add [email protected]:dfed/Relativity.git`, drag Relativity.xcodeproj to your project, and add Relativity as a build dependency.
## Contributing
I’m glad you’re interested in Relativity, and I’d love to see where you take it. Please read the [contributing guidelines](Contributing.md) prior to submitting a Pull Request.
Thanks, and happy positioning!
## Default branch
The default branch of this repository is `main`. Between the initial commit and [7b113bc](https://github.com/dfed/Relativity/commit/7b113bc644ebfd5981231f06c946ad9bc9d262f2), the default branch of this repository was `master`. See #19 for more details on why this change was made.
## Attribution
Shout out to [Peter Westen](https://twitter.com/pwesten) who inspired the creation of this library.