SnapKit/docs.md

---
layout: default
permalink: /docs/
id: docs
---
## Requirements

* iOS 7.0+ / OS X 10.9+
* Xcode 6.3+

> While SnapKit supports iOS 7.0, frameworks are not supported for iOS 7.0 so you must use manually embed the framework for non app store apps or integrate the source files directly.

## Installing

The first thing you’ll need to do with SnapKit is get it installed into your project. We support three different integrations:

### 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
```

### 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)
    make.bottom.equalTo(superview).offset(20)
    make.right.equalTo(superview).offset(20)
}
```

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)
```

### 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) -> 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)
    }
  }
}
```