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<img src="http://snapkit.io/images/banner.png" alt="" />
<div style="padding: 40px 0; background-color: #0091BD; background-image: -webkit-linear-gradient(90deg, #00C7B5 0, #0056C7 100%); background-image: linear-gradient(90deg, #00C7B5 0, #0056C7 100%); text-align: center; "> SnapKit is a DSL to make Auto Layout easy on both iOS and OS X.
<img src="http://snapkit.io/images/logo_2x.png" width="539" height="128" alt="SnapKit" />
</div>
====
[![Build Status](https://travis-ci.org/SnapKit/SnapKit.svg)](https://travis-ci.org/SnapKit/SnapKit) [![Build Status](https://travis-ci.org/SnapKit/SnapKit.svg)](https://travis-ci.org/SnapKit/SnapKit)
SnapKit is a light-weight layout framework which wraps AutoLayout with a nicer syntax. SnapKit has its own layout DSL which provides a chainable way of describing your NSLayoutConstraints which results in layout code that is more concise and readable. SnapKit supports both iOS and OS X.
> SnapKit uses some Swift-only features like function overloading, so it cannot be used from Objective-C. Because of this we’ve chosen to swap prefixes from Masonry’s `mas_` to `snp_` so you can use both Masonry and SnapKit in the same project.
## Requirements
* iOS 7.0+ / Mac OS X 10.9+
* Xcode 6.1
## Installation
> **Embedded frameworks require a minimum deployment target of iOS 8 or OS X Mavericks.**
### CocoaPods
[CocoaPods](http://cocoapods.org) is a dependency manager for Cocoa projects.
CocoaPods 0.36 adds supports for Swift and embedded frameworks. You can install it with the following command:
```bash
$ gem install cocoapods
```
To integrate SnapKit into your Xcode project using CocoaPods, specify it in your `Podfile`:
```ruby
source 'https://github.com/CocoaPods/Specs.git'
platform :ios, '8.0'
use_frameworks!
pod 'SnapKit', '~> 0.10.0'
```
Then, run the following command:
```bash
$ pod install
```
### Carthage
Carthage is a decentralized dependency manager that automates the process of adding frameworks to your Cocoa application.
You can install Carthage with [Homebrew](http://brew.sh/) using the following command:
```bash
$ brew update
$ brew install carthage
```
To integrate SnapKit into your Xcode project using Carthage, specify it in your `Cartfile`:
```
github "SnapKit/SnapKit" >= 0.10.0
```
### Manually
If you prefer not to use either of the aforementioned dependency managers, you can integrate SnapKit into your project manually.
### Embedded Framework
- Add SnapKit as a [submodule](http://git-scm.com/docs/git-submodule) by opening the Terminal, `cd`-ing into your top-level project directory, and entering the following command:
```bash
$ git submodule add https://github.com/SnapKit/SnapKit.git
```
- Open the `SnapKit` folder, and drag `SnapKit.xcodeproj` into the file navigator of your app project.
- In Xcode, navigate to the target configuration window by clicking on the blue project icon, and selecting the application target under the "Targets" heading in the sidebar.
- Ensure that the deployment target of SnapKit.framework matches that of the application target.
- In the tab bar at the top of that window, open the "Build Phases" panel.
- Expand the "Target Dependencies" group, and add `SnapKit.framework`.
- Click on the `+` button at the top left of the panel and select "New Copy Files Phase". Rename this new phase to "Copy Frameworks", set the "Destination" to "Frameworks", and add `SnapKit.framework`.
## What's wrong with NSLayoutConstraints?
Under the hood Auto Layout is a powerful and flexible way of organising and laying out your views. However creating constraints from code is verbose and not very descriptive.
Imagine a simple example in which you want to have a view fill its superview but inset by 10 pixels on every side
```swift ```swift
let superview = self; import SnapKit
let view1 = UIView() class MyViewController: UIViewController {
view1.setTranslatesAutoresizingMaskIntoConstraints(false)
view1.backgroundColor = UIColor.greenColor()
superview.addSubview(view1)
let padding = UIEdgeInsetsMake(10, 10, 10, 10) lazy var box = UIView()
superview.addConstraints([
NSLayoutConstraint(
item: view1,
attribute: NSLayoutAttribute.Top,
relatedBy: NSLayoutRelation.Equal,
toItem: superview,
attribute: NSLayoutAttribute.Top,
multiplier: 1.0,
constant: padding.top
),
NSLayoutConstraint(
item: view1,
attribute: NSLayoutAttribute.Left,
relatedBy: NSLayoutRelation.Equal,
toItem: superview,
attribute: NSLayoutAttribute.Left,
multiplier: 1.0,
constant: padding.left
),
NSLayoutConstraint(
item: view1,
attribute: NSLayoutAttribute.Bottom,
relatedBy: NSLayoutRelation.Equal,
toItem: superview,
attribute: NSLayoutAttribute.Bottom,
multiplier: 1.0,
constant: -padding.bottom
),
NSLayoutConstraint(
item: view1,
attribute: NSLayoutAttribute.Right,
relatedBy: NSLayoutRelation.Equal,
toItem: superview,
attribute: NSLayoutAttribute.Right,
multiplier: 1.0,
constant: -padding.right
)
])
```
Even with such a simple example the code needed is quite verbose and quickly becomes unreadable when you have more than 2 or 3 views.
Another option is to use Visual Format Language (VFL), which is a bit less long winded.
However the ASCII type syntax has its own pitfalls and its also a bit harder to animate as `NSLayoutConstraint.constraintsWithVisualFormat` returns an array.
## Prepare to meet your Maker!
Heres the same constraints created using ConstraintMaker
```swift
let padding = UIEdgeInsetsMake(10, 10, 10, 10)
view1.snp_makeConstraints { (make) -> Void in
make.top.equalTo(superview.snp_top).offset(padding.top)
make.left.equalTo(superview.snp_left).offset(padding.left)
make.bottom.equalTo(superview.snp_bottom).offset(-padding.bottom)
make.right.equalTo(superview.snp_right).offset(-padding.right)
}
```
Or even shorter
```swift
view1.snp_makeConstraints { (make) -> Void in
make.edges.equalTo(superview).insets(padding)
}
```
Also note in the first example we had to add the constraints to the superview `superview.addConstraints`.
SnapKit however will automagically add constraints to the appropriate view.
SnapKit will also call `view1.setTranslatesAutoresizingMaskIntoConstraints(false)` for you.
## Not all things are created equal
> `.equalTo` equivalent to **NSLayoutRelation.Equal**
> `.lessThanOrEqualTo` equivalent to **NSLayoutRelation.LessThanOrEqual**
> `.greaterThanOrEqualTo` equivalent to **NSLayoutRelation.GreaterThanOrEqual**
These three equality constraints accept one argument which can be any of the following:
#### 1. ViewAttribute
```swift
make.centerX.lessThanOrEqualTo(view2.snp_left)
```
ViewAttribute | NSLayoutAttribute
------------------------- | --------------------------
view.snp_left | NSLayoutAttribute.Left
view.snp_right | NSLayoutAttribute.Right
view.snp_top | NSLayoutAttribute.Top
view.snp_bottom | NSLayoutAttribute.Bottom
view.snp_leading | NSLayoutAttribute.Leading
view.snp_trailing | NSLayoutAttribute.Trailing
view.snp_width | NSLayoutAttribute.Width
view.snp_height | NSLayoutAttribute.Height
view.snp_centerX | NSLayoutAttribute.CenterX
view.snp_centerY | NSLayoutAttribute.CenterY
view.snp_baseline | NSLayoutAttribute.Baseline
#### 2. UIView/NSView
if you want view.left to be greater than or equal to label.left :
```swift
// these two constraints are exactly the same
make.left.greaterThanOrEqualTo(label)
make.left.greaterThanOrEqualTo(label.snp_left)
```
#### 3. Strict Checks
Auto Layout allows width and height to be set to constant values.
if you want to set view to have a minimum and maximum width you could pass a primitive to the equality blocks:
```swift
// width >= 200 && width <= 400
make.width.greaterThanOrEqualTo(200)
make.width.lessThanOrEqualTo(400)
```
However Auto Layout does not allow alignment attributes such as left, right, centerY etc to be set to constant values.
So if you pass a primitive for these attributes SnapKit will turn these into constraints relative to the view&rsquo;s superview ie:
```swift
// creates view.left <= view.superview.left + 10
make.left.lessThanOrEqualTo(10)
```
You can also use other primitives and structs to build your constraints, like so:
```swift
make.top.equalTo(42)
make.height.equalTo(20)
make.size.equalTo(CGSizeMake(50, 100))
make.edges.equalTo(UIEdgeInsetsMake(10, 0, 10, 0))
make.left.equalTo(view).offset(UIEdgeInsetsMake(10, 0, 10, 0))
```
## Learn to prioritize
> `.prority` allows you to specify an exact priority
> `.priorityHigh` equivalent to **UILayoutPriority.DefaultHigh**
> `.priorityMedium` is half way between high and low
> `.priorityLow` equivalent to **UILayoutPriority.DefaultLow**
Priorities are can be tacked on to the end of a constraint chain like so:
```swift
make.left.greaterThanOrEqualTo(label.snp_left).priorityLow();
make.top.equalTo(label.snp_top).priority(600);
```
## Composition, composition, composition
SnapKit also gives you a few convenience methods which create multiple constraints at the same time.
#### edges
```swift
// make top, left, bottom, right equal view2
make.edges.equalTo(view2);
// make top = superview.top + 5, left = superview.left + 10,
// bottom = superview.bottom - 15, right = superview.right - 20
make.edges.equalTo(superview).insets(UIEdgeInsetsMake(5, 10, 15, 20))
```
#### size
```swift
// make width and height greater than or equal to titleLabel
make.size.greaterThanOrEqualTo(titleLabel)
// make width = superview.width + 100, height = superview.height - 50
make.size.equalTo(superview).offset(CGSizeMake(100, -50))
```
#### center
```swift
// make centerX and centerY = button1
make.center.equalTo(button1)
// make centerX = superview.centerX - 5, centerY = superview.centerY + 10
make.center.equalTo(superview).offset(CGPointMake(-5, 10))
```
You can chain view attributes for increased readability:
```swift
// All edges but the top should equal those of the superview
make.left.right.bottom.equalTo(superview)
make.top.equalTo(otherView)
```
## Hold on for dear life
Sometimes you need modify existing constraints in order to animate or remove/replace constraints.
In SnapKit there are a few different approaches to updating constraints.
#### 1. References
You can hold on to a reference of a particular constraint by assigning the result of a constraint make expression to a local variable or a class property.
You could also reference multiple constraints by storing them away in an array.
```swift
var topConstraint: Constraint? = nil
...
// when making constraints
view1.snp_makeConstraints { make in
self.topConstraint = make.top.equalTo(superview).offset(padding.top).constraint
make.left.equalTo(superview).offset(padding.left)
}
...
// then later you can call
self.topConstraint.uninstall()
```
### 2. snp_remakeConstraints
`snp_remakeConstraints` is similar to `snp_makeConstraints`, but will first remove all existing constraints installed by SnapKit.
```swift
func changeButtonPosition() {
self.button.snp_remakeConstraints { make in
make.size.equalTo(self.buttonSize)
if topLeft {
make.top.left.equalTo(10)
} else {
make.bottom.equalTo(self.view).offset(-10)
make.right.equalTo(self.view).offset(-10)
}
}
}
```
## Code Snippets
Copy the included code snippets to ``~/Library/Developer/Xcode/UserData/CodeSnippets`` to write your snap closures at lightning speed!
`snp_make` -> `<view>.snp_makeConstraints { make in <code> }`
`snp_remake` -> `<view>.snp_remakeConstraints { make in <code> }` override func viewDidLoad() {
super.viewDidLoad()
self.view.addSubview(box)
box.snp_makeConstraints { (make) -> Void in
make.width.height.equalTo(50)
make.center.equalTo(self.view)
}
}
## TODO }
```
* Eye candy ## Resources
* Example projects
* Tests * [Documentation](http://snapkit.io/docs/)
* [F.A.Q.](http://snapkit.io/faq/)
## License
MIT license. See the `LICENSE` file for details.