mirror of https://github.com/SnapKit/SnapKit
304 lines
8.7 KiB
Markdown
304 lines
8.7 KiB
Markdown
---
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layout: default
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permalink: /docs/
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id: docs
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---
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## Requirements
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- iOS 8.0+ / Mac OS X 10.11+ / tvOS 9.0+
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- Xcode 8.0+
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- Swift 3.0+
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## Migration Guides
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- [SnapKit 3.0 Migration Guide](https://github.com/SnapKit/SnapKit/blob/master/Documentation/SnapKit%203.0%20Migration%20Guide.md)
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## Communication
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- If you **need help**, use [Stack Overflow](http://stackoverflow.com/questions/tagged/snapkit). (Tag 'snapkit')
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- If you'd like to **ask a general question**, use [Stack Overflow](http://stackoverflow.com/questions/tagged/snapkit).
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- If you **found a bug**, open an issue.
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- If you **have a feature request**, open an issue.
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- If you **want to contribute**, submit a pull request.
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## Installation
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### CocoaPods
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[CocoaPods](http://cocoapods.org) is a dependency manager for Cocoa projects. You can install it with the following command:
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```bash
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$ gem install cocoapods
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```
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> CocoaPods 1.1.0+ is required to build SnapKit 3.0.0+.
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To integrate SnapKit into your Xcode project using CocoaPods, specify it in your `Podfile`:
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```ruby
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source 'https://github.com/CocoaPods/Specs.git'
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platform :ios, '10.0'
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use_frameworks!
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target '<Your Target Name>' do
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pod 'SnapKit', '~> 3.0'
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end
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```
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Then, run the following command:
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```bash
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$ pod install
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```
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### Carthage
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[Carthage](https://github.com/Carthage/Carthage) is a decentralized dependency manager that builds your dependencies and provides you with binary frameworks.
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You can install Carthage with [Homebrew](http://brew.sh/) using the following command:
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```bash
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$ brew update
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$ brew install carthage
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```
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To integrate SnapKit into your Xcode project using Carthage, specify it in your `Cartfile`:
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```ogdl
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github "SnapKit/SnapKit" ~> 3.0
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```
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Run `carthage update` to build the framework and drag the built `SnapKit.framework` into your Xcode project.
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### Manually
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If you prefer not to use either of the aforementioned dependency managers, you can integrate SnapKit into your project manually.
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---
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## Usage
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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.
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```
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let box = UIView()
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superview.addSubview(box)
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box.snp.makeConstraints { (make) -> Void in
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make.top.equalTo(superview).offset(20)
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make.left.equalTo(superview).offset(20)
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make.bottom.equalTo(superview).offset(-20)
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make.right.equalTo(superview).offset(-20)
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}
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```
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Or even shorter:
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```
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let box = UIView()
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superview.addSubview(box)
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box.snp.makeConstraints { (make) -> Void in
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make.edges.equalTo(superview).inset(UIEdgeInsetsMake(20, 20, 20, 20))
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}
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```
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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:
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- Determining the best common superview to install the constraints on.
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- Keeping track of the constrainted installed so they can easily be removed later.
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- Ensuring `setTranslatesAutoresizingMaskIntoConstraints(false)` is called on all appropriate views.
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### Not all things are created equal
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> `.equalTo` equivalent to **NSLayoutRelation.Equal**
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> `.lessThanOrEqualTo` equivalent to **NSLayoutRelation.LessThanOrEqual**
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> `.greaterThanOrEqualTo` equivalent to **NSLayoutRelation.GreaterThanOrEqual**
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These three equality constraints accept one argument which can be any of the following:
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#### 1. ViewAttribute
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```
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make.centerX.lessThanOrEqualTo(view2.snp.left)
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```
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ViewAttribute | NSLayoutAttribute
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------------------------- | --------------------------
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view.snp.left | NSLayoutAttribute.left
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view.snp.right | NSLayoutAttribute.right
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view.snp.top | NSLayoutAttribute.top
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view.snp.bottom | NSLayoutAttribute.bottom
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view.snp.leading | NSLayoutAttribute.leading
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view.snp.trailing | NSLayoutAttribute.trailing
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view.snp.width | NSLayoutAttribute.width
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view.snp.height | NSLayoutAttribute.height
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view.snp.centerX | NSLayoutAttribute.centerX
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view.snp.centerY | NSLayoutAttribute.centerY
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view.snp.lastBaseline | NSLayoutAttribute.lastBaseline
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#### 2. UIView/NSView
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if you want view.left to be greater than or equal to label.left:
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```
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// these two constraints are exactly the same
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make.left.greaterThanOrEqualTo(label)
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make.left.greaterThanOrEqualTo(label.snp.left)
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```
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#### 3. Strict Checks
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Auto Layout allows width and height to be set to constant values.
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if you want to set view to have a minimum and maximum width you could pass a primitive to the equality blocks:
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```
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// width >= 200 && width <= 400
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make.width.greaterThanOrEqualTo(200)
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make.width.lessThanOrEqualTo(400)
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```
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However Auto Layout does not allow alignment attributes such as left, right, centerY etc to be set to constant values.
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So if you pass a primitive for these attributes SnapKit will turn these into constraints relative to the view's superview ie:
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```
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// creates view.left <= view.superview.left + 10
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make.left.lessThanOrEqualTo(10)
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```
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You can also use other primitives and structs to build your constraints, like so:
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```
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make.top.equalTo(42)
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make.height.equalTo(20)
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make.size.equalTo(CGSize(width: 50, height: 100))
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make.edges.equalTo(UIEdgeInsets(top: 10, left: 0, bottom: 10, right: 0))
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make.left.equalTo(view).offset(UIEdgeInsets(top: 10, left: 0, bottom: 10, right: 0))
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```
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### Learn to prioritize
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> `.priority` allows you to specify an exact priority
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Priorities are can be tacked on to the end of a constraint chain like so:
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```
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make.top.equalTo(label.snp.top).priority(600)
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```
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### Composition, composition, composition
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SnapKit also gives you a few convenience methods to create multiple constraints at the same time.
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#### edges
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```
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// make top, left, bottom, right equal view2
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make.edges.equalTo(view2);
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// make top = superview.top + 5, left = superview.left + 10,
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// bottom = superview.bottom - 15, right = superview.right - 20
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make.edges.equalTo(superview).inset(UIEdgeInsets(top: 5, left: 10, bottom: 15, right: 20))
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```
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#### size
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```
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// make width and height greater than or equal to titleLabel
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make.size.greaterThanOrEqualTo(titleLabel)
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// make width = superview.width + 100, height = superview.height + 100
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make.size.equalTo(superview).offset(100)
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```
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#### center
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```
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// make centerX and centerY = button1
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make.center.equalTo(button1)
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// make centerX = superview.centerX + 5, centerY = superview.centerY + 5
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make.center.equalTo(superview).offset(5)
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```
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You can chain view attributes for increased readability:
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```
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// All edges but the top should equal those of the superview
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make.left.right.bottom.equalTo(superview)
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make.top.equalTo(otherView)
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```
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### Hold on for dear life
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Sometimes you need modify existing constraints in order to animate or remove/replace constraints.
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In SnapKit there are a few different approaches to updating constraints.
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#### 1. References
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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.
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You could also reference multiple constraints by storing them away in an array.
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```
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var topConstraint: Constraint? = nil
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...
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// when making constraints
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view1.snp.makeConstraints { (make) -> Void in
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self.topConstraint = make.top.equalTo(superview).offset(padding.top).constraint
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make.left.equalTo(superview).offset(padding.left)
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}
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...
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// then later you can call
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self.topConstraint.uninstall()
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// or if you want to update the constraint
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self.topConstraint.updateOffset(5)
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```
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### 2. snp.updateConstraints
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Alternative if you are only updating the **constant** value of the constraint you can use the method `snp.updateConstraints` instead of `snp.makeConstraints`
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```
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// this is Apple's recommended place for adding/updating constraints
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// this method can get called multiple times in response to setNeedsUpdateConstraints
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// 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
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make.center.equalTo(self);
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make.width.equalTo(self.buttonSize.width).priority(250)
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make.height.equalTo(self.buttonSize.height).priority(250)
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make.width.lessThanOrEqualTo(self)
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make.height.lessThanOrEqualTo(self)
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}
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// according to Apple super should be called at end of method
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super.updateConstraints()
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}
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```
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### 3. snp.remakeConstraints
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`snp.remakeConstraints` is similar to `snp.makeConstraints`, but will first remove all existing constraints installed by SnapKit.
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```
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func changeButtonPosition() {
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self.button.snp.remakeConstraints { (make) -> Void in
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make.size.equalTo(self.buttonSize)
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if topLeft {
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make.top.left.equalTo(10)
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} else {
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make.bottom.equalTo(self.view).offset(-10)
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make.right.equalTo(self.view).offset(-10)
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}
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}
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}
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```
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