constraints-kit

Declarative, Chainable & Lightweight Auto Layout constraints framework for iOS. The framework offers a rich set of methods for defining Auto Layout constraints (see Contents) without any other external dependencies.

? Movitation

The purpose of this framework is to provide a very lightweight solution for Auto Layout and to make the development of programmatic UI much simpler, hiding the boilerplate code under the framework. Primary usage is for internal developments, however I decided to share the framework with the community, since it offers some uniqueness and I'm going to continue work on this development.

? Demo

In order to create something like in the following screenshot:

constraints-kit-1

You need to write just a few lines of code:

// 1. First you need to add all your views somewhere. That means your views must have a superview. Let's assume that you have done that. 

// 2. Then we assume that visually your views are fully configured. 

// 3. And finally, all we need to do is to specify the constraints:

cardView.pinInside(view: self.view, offset: 16)

imageView.pinInside(view: cardView, offset: 8)

blurView.pinInside(view: cardView)
    
titleLabel.pinTopToTopCenter(of: imageView, offset: 24)
    
button
        .bottom(with:   imageView, anchor:  .bottom,    offset: -34)
        .center(in:     imageView, axis:    .horizontal)
        .set(height:    60)
        .set(aspect:    2/1)
            
label
        .center(in:     imageView)
        .left(with:     imageView, anchor: .left,   offset:  16)
        .right(with:    imageView, anchor: .right,  offset: -16)

Installation

CocoaPods

constraints-kit is availabe via CocoaPods

pod 'constraints-kit', '~> 1.0.0'

Manual

You can always manually add the framework sources into your project. In order to do that just simply copy-paste the following files.

✈️ Usage

The framework is pretty easy to use, however I do recommend to learn the basics of Auto Layout before installing the framework - it will help you to understand what the minimum number of constraints a UIView needs to have and to avoid common pitfalls.

Import

After adding the framework to a project, simply add an import statemt:

import constraints_kit

Setting size

view.set(size: CGSize(width: 300, height: 300))

view.set(width: 400)

view.set(height: 200)

view
    .set(width:  200)
    .set(aspect: 2/1)

Constraining

A UIImageView fills the parent UIView with offset, until the bottom anchor reaches the top anchor of the UIButton:

imageView
    .constrain(using: .top,     to: .top,   of: view,   offset:  24)
    .constrain(using: .right,   to: .right, of: view,   offset: -24)
    .constrain(using: .left,    to: .left,  of: view,   offset:  24)
    .constrain(using: .bottom,  to: .top,   of: button, offset: -24)

A UIImageView is anchored at the center of the parent view, it's stretched to the horizontal axis by anchoring left & right sides with the aspect ratio of 3 to 2:

imageView
    .center(in:   view, axis:   .vertical)
    .left(with:   view, anchor: .left)
    .right(with:  view, anchor: .right)
    .set(aspect: 3/2)

Anchoring

A custom UIView fills a UICollectionViewCell to the top system spacing, with custom left & right offsets and to the top anchor of the UIButton:

presenterView
    .topToSystemSpacing(with: view,   anchor: .top)
    .right(             with: view,   anchor: .right, offset: -16)
    .left(              with: view,   anchor: .left,  offset:  16)
    .bottom(            with: button, anchor: .top,   offset: -16)

A UIButton is placed at the center of the parent view, its bottom anchor is attached to the bottom of the parent view, height is set to 60 with aspect ratio of 2 to 1:

button
    .bottom(with: imageView, anchor:  .bottom,    offset: -34)
    .center(in:   imageView, axis:    .horizontal)
    .set(height: 60)
    .set(aspect: 2/1)

Pinning

A custom ActivityIndicator view is anchored to the top left corner of the specified view with some offset and size equals to 20 to 20:

activityIndicator
    .pinInsideToTopLeftCorner(of: view, offset: 24)
    .size(CGSize(width: 20, height: 20))

Advanced case where top left anchor of a custom ProgressView is attached to the top leading corner of the parent view and the bottom right anchor is attached to the top right anchor of the LogIn button:

progressView
    .pin(anchors: [.left,   .top],    toTargetView: view,   using: [.leading, .top])
    .pin(anchors: [.bottom, .right],  toTargetView: button, using: [.right,   .top])

Filling

A UITableView is placed inside the parent UIView and fills the top half of it (using left, top, right and centerX anchors):

tableView.fillTopHalf(of: parentView)

A UICollectionView is placed inside the parent UIView and fills the left half of it with the specified offset (using left, top, bottom and centerY anchors):

collectionView.fillLeftHalf(of: splitView, offset: 16)

? Contents

The kit contains several groups of methods, each with a specific purpose. All the groups can be chained together, however you should keep in mind that if you have conflicting constraints or you don't provide enough information for the Auto Layout engine, you will see no effect or some unexpected results. It's assumed that you already know the basics of Auto Layout.

Common

  • constrain - constrains self using the specified Attribute to the specified Attribute with respect to the related UIView. You may set Relation (which is by default .equal), offset (default is 0.0) and multiplier (default is 1.0)
  • fit - places self inside the specified UIView with an optional offset (default is 0.0)
  • center - centers self inside the specified UIView using a concrete Axis case, with an optional multiplier (default is 1.0)
  • width - applies width equalization between self and the specified UIView. You may change the Relation (default is equal), UILayoutPriority (default is required), multiplier (default is 1.0) and constant (default is 0.0)
  • height - applies height equalization between self and the specified UIView. You may change the Relation (default is equal), UILayoutPriority (default is required), multiplier (default is 1.0) and constant (default is 0.0)

Setters

  • set(size:) - sets a new CGSize for self by applying layout constaints for width & height anchors
  • set(width:) - sets a new width by applying layout constaint for width anchor
  • set(height:) - sets a new height by applying layout constraint for height anchor
  • set(aspect:) - sets a new aspect ratio by applying layout constaint for aspect anchor
  • set(aspectOf:) - sets a new aspect ratio by duplicating aspect of the specified UIView
  • set(value: to:) - sets a new offset value for the Attribute

Anchoring

  • top - anchors top anchor to the specified UIView using AxisY anchor, Relation (defatul is .equal), NSLayoutPriority (default is .required) and offset (default is 0.0)
  • bottom - anchors bottom anchor to the specified UIView using AxisY anchor, Relation (defatul is .equal), NSLayoutPriority (default is .required) and offset (default is 0.0)
  • left - anchors left anchor to the specified UIView using AxisY anchor, Relation (defatul is .equal), NSLayoutPriority (default is .required) and offset (default is 0.0)
  • right - anchors right anchor to the specified UIView using AxisY anchor, Relation (defatul is .equal), NSLayoutPriority (default is .required) and offset (default is 0.0)

Anchoring to System Spacing

  • rightToSystemSpacing - anchors right anchor to the specified UIView with respect to System Spacing using AxisY anchor, Relation (defatul is .equal), NSLayoutPriority (default is .required) and offset (default is 0.0)
  • leftToSystemSpacing - anchors left anchor to the specified UIView with respect to System Spacing using AxisY anchor, Relation (defatul is .equal), NSLayoutPriority (default is .required) and offset (default is 0.0)
  • topToSystemSpacing - anchors top anchor to the specified UIView with respect to System Spacing using AxisY anchor, Relation (defatul is .equal), NSLayoutPriority (default is .required) and offset (default is 0.0)
  • bottomToSystemSpacing - anchors bottom anchor to the specified UIView with respect to System Spacing using AxisY anchor, Relation (defatul is .equal), NSLayoutPriority (default is .required) and offset (default is 0.0)

Pinning

  • pinTopLeftToTopLeftCorner - pins Top Left anchor to the Top Left corner of the specified UIView with a given offset (default is 0.0)
  • pinTopRightToTopRightCorner - pins Top Right anchor to the Top Right corner of the specified UIView with a given offset (default is 0.0)
  • pinBottomRightToBottomRight - pins Bottom Right anchor to the Bottom Right corner of the specified UIView with a given offset (default is 0.0)
  • pinBottomLeftToBottomLeft - pins Bottom Left anchor to the Bottom Left corner of the specified UIView with a given offset (default is 0.0)
  • pinBottomRightToTopLeft - pins Bottom Right anchor to the Top Left corner of the specified UIView with a given offset (default is 0.0)
  • pinBottomLeftToTopRight - pins Bottom Left anchor to the Top Right corner of the specified UIView with a given offset (default is 0.0)
  • pinTopLeftToBottomRight - pins Top Left anchor to the Bottom Right corner of the specified UIView with a given offset (default is 0.0)
  • pinBottomRightToTopLeft - pins Bottom Right anchor to the Top Left corner of the specified UIView with a given offset (default is 0.0)
  • pinTopToTopCenter - pins Top anchor to the Top Center anchor of the specified UIView with a given offset (default is 0.0)
  • pinBottomToBottomCenter - pins Bottom anchor to the Bottom Center anchor of the specified UIView with a given offset (default is 0.0)
  • pinLeftToLeftCenter - pins Left anchor to the Left Center anchor of the specified UIView with a given offset (default is 0.0)
  • pinRightToRightCenter - pins Right anchor to the Right Center anchor of the specified UIView with a given offset (default is 0.0)
  • pinInside - pins self inside the specified UIView with Relation (default is .equal), UILayoutPriority (default is .required) and offset (default is 0.0)
  • pinTo - pins self to the specified UIView by using Anchor (which is an OptionSet)
  • pin(anchors:, toTargetView: , using:) - pins the specified Anchors of self to the UIView by using the related Anchors

Filling

  • fillBottomHalf - fills the bottom half of the specified view by self with the given offset (default is 0.0)
  • fillTopHalf - fills the top half of the specified view by self with the given offset (default is 0.0)
  • fillLeftHalf - fills the left half of the specified view by self with the given offset (default is 0.0)
  • fillRightHalf - fills the right half of the specified view by self with the given offset (default is 0.0)

GitHub