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---
layout: default
permalink: /docs/
id: docs
---
## Requirements
* iOS 7.0+ / OS X 10.9+
* Xcode 6.3+
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> While SnapKit supports iOS 7.0, frameworks are not supported for iOS 7.0 so you must manually embed the framework for non app store apps or integrate the source files directly.
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## Installing
The first thing you’
### 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!
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pod 'SnapKit', '~> 0.12.0'
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```
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` :
```
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github "SnapKit/SnapKit" >= 0.12.0
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```
### 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` .
## Usage
SnapKit is designed to be extremely easy to use. Let's say we want to layout a box that is constrained to it's superview's edges with 20pts of padding.
```swift
let box = UIView()
superview.addSubview(box)
box.snp_makeConstraints { (make) -> Void in
make.top.equalTo(superview).offset(20)
make.left.equalTo(superview).offset(20)
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make.bottom.equalTo(superview).offset(-20)
make.right.equalTo(superview).offset(-20)
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}
```
Or even shorter:
```swift
let box = UIView()
superview.addSubview(box)
box.snp_makeConstraints { (make) -> Void in
make.edges.equalTo(superview).inset(UIEdgeInsetsMake(20, 20, 20, 20))
}
```
Not only does this greatly shorten and increase the readability of constraints SnapKit is also taking care of a few crucial steps in the process:
- Determining the best common superview to install the constraints on.
- Keeping track of the constrainted installed so they can easily be removed later.
- Ensuring `setTranslatesAutoresizingMaskIntoConstraints(false)` is called on all appropriate views.
### 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'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 to 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) -> Void 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()
// or if you want to update the constraint
self.topConstraint.updateOffset(5)
```
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### 2. snp_updateConstraints
Alternative if you are only updating the **constant** value of the constraint you can use the method `snp_updateConstraints` instead of `snp_makeConstraints`
```swift
// this is Apple's recommended place for adding/updating constraints
// this method can get called multiple times in response to setNeedsUpdateConstraints
// which can be called by UIKit internally or in your code if you need to trigger an update to your constraints
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override func updateConstraints() {
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self.growingButton.snp_updateConstraints { (make) -> Void in
make.center.equalTo(self);
make.width.equalTo(self.buttonSize.width).priorityLow()
make.height.equalTo(self.buttonSize.height).priorityLow()
make.width.lessThanOrEqualTo(self)
make.height.lessThanOrEqualTo(self)
}
// according to apple super should be called at end of method
super.updateConstraints()
}
```
### 3. snp_remakeConstraints
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`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) -> Void 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)
}
}
}
```
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## Features
* Not limited to a subset of Auto Layout. Anything NSLayoutConstraint can do SnapKit can also do.
* Better debugging support to help find breaking constraints.
* No crazy operator overloads.
* Not string or dictionary based and you get the strictest compile time checks possible.
## TODO
* Example Projects
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* Better Debugging Support
