Auto Layout in Swift

AutoLayout.swift

//
//  AutoLayout.swift
//  Tobias Due Munk
//
//  Created by Tobias Due Munk on 26/08/14.
//  Copyright (c) 2014 Tobias Due Munk. All rights reserved.
//
//  Example usage:
//
//  view1.topInset(20, relation: .Equal, priority: 200)
//  view1.topInset(20, relation: .GreaterThanOrEqual)
//  view1.horizontalInset(0)
//  view2.horizontalInset(0)
//  view2.topOffset(view1, value: 0)
//  view2.heightEqual(view1)
// 
//  or
// 
//  view.inset(top: 0, left: 10)
//  view.width(100, .GreaterThanOrEqual)

import UIKit


extension UIView {

    /* Inset */
    func inset(insetValue: Float, priority: UILayoutPriority = 1000) {
        inset(top: insetValue, left: insetValue, bottom: insetValue, right: insetValue, priority: priority)
    }
    func inset(top: Float? = nil, left: Float? = nil, bottom: Float? = nil, right: Float? = nil, margin: Bool = false, relation: NSLayoutRelation = .Equal, priority: UILayoutPriority = 1000) {
        if let left = left {
            leftInset(left, margin: margin, relation: relation, priority: priority)
        }
        if let top = top {
            topInset(top, margin: margin, relation: relation, priority: priority)
        }
        if let right = right {
            rightInset(right, margin: margin, relation: relation, priority: priority)
        }
        if let bottom = bottom {
            bottomInset(bottom, margin: margin, relation: relation, priority: priority)
        }
    }
    func horizontalInset(_ insetValue: Float = 0, margin: Bool = false, relation: NSLayoutRelation = .Equal, priority: UILayoutPriority = 1000) {
        inset(left: 0, right: 0, margin: margin, relation: relation, priority: priority)
    }
    func verticalInset(_ insetValue: Float = 0, margin: Bool = false, relation: NSLayoutRelation = .Equal, priority: UILayoutPriority = 1000) {
        inset(top: 0, bottom: 0, margin: margin, relation: relation, priority: priority)
    }
    func leftInset(_ value: Float = 0, margin: Bool = false, relation: NSLayoutRelation = .Equal, priority: UILayoutPriority = 1000) {
        inset(margin ? .LeftMargin : .Left, value: value, relation: relation, priority: priority)
    }
    func topInset(_ value: Float = 0, margin: Bool = false, relation: NSLayoutRelation = .Equal, priority: UILayoutPriority = 1000) {
        inset(margin ? .TopMargin : .Top, value: value, relation: relation, priority: priority)
    }
    func rightInset(_ value: Float = 0, margin: Bool = false, relation: NSLayoutRelation = .Equal, priority: UILayoutPriority = 1000) {
        let (flippedValue, flippedRelation) = flip(value: value, relation: relation)
        inset(margin ? .RightMargin : .Right, value: flippedValue, relation: flippedRelation, priority: priority)
    }
    func bottomInset(_ value: Float = 0, margin: Bool = false, relation: NSLayoutRelation = .Equal, priority: UILayoutPriority = 1000) -> NSLayoutConstraint {
        let (flippedValue, flippedRelation) = flip(value: value, relation: relation)
        return inset(margin ? .BottomMargin : .Bottom, value: flippedValue, relation: flippedRelation, priority: priority)
    }
    func bottomBaselineInset(_ value: Float = 0, relation: NSLayoutRelation = .Equal, priority: UILayoutPriority = 1000) {
        let (flippedValue, flippedRelation) = flip(value: value, relation: relation)
        inset(.Baseline, value: flippedValue, relation: flippedRelation, secondAttribute: .Bottom, priority: priority)
    }
    private func inset(attribute: NSLayoutAttribute, value: Float = 0, relation: NSLayoutRelation = .Equal, priority: UILayoutPriority = 1000) -> NSLayoutConstraint {
        let constraint = NSLayoutConstraint(item: self, attribute: attribute, relatedBy: relation, toItem: self.superview, attribute: attribute, multiplier: 1, constant: CGFloat(value))
        constraint.priority = priority
        return installConstraint(constraint)
    }
    private func inset(attribute: NSLayoutAttribute, value: Float = 0, relation: NSLayoutRelation = .Equal, secondAttribute: NSLayoutAttribute, priority: UILayoutPriority = 1000) -> NSLayoutConstraint {
        let constraint = NSLayoutConstraint(item: self, attribute: attribute, relatedBy: relation, toItem: self.superview, attribute: secondAttribute, multiplier: 1, constant: CGFloat(value))
        constraint.priority = priority
        return installConstraint(constraint)
    }

    /* Height and width */
    func width(width: Float, relation: NSLayoutRelation = .Equal, priority: UILayoutPriority = 1000) {
        dimension(.Width, value: width, relation: relation, priority: priority)
    }
    func height(height: Float, relation: NSLayoutRelation = .Equal, priority: UILayoutPriority = 1000) {
        dimension(.Height, value: height, relation: relation, priority: priority)
    }
    private func dimension(attribute: NSLayoutAttribute, value: Float, relation: NSLayoutRelation, priority: UILayoutPriority = 1000) -> NSLayoutConstraint {
        let constraint = NSLayoutConstraint(item: self, attribute: attribute, relatedBy: relation, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: CGFloat(value))
        constraint.priority = priority
        return installConstraint(constraint)
    }

    /* Center */
    func center(relation: NSLayoutRelation = .Equal, priority: UILayoutPriority = 1000) {
        centerX(priority: priority)
        centerY(priority: priority)
    }
    func centerX(relation: NSLayoutRelation = .Equal, priority: UILayoutPriority = 1000) {
        center(.CenterX, relation: relation, priority: priority)
    }
    func centerY(relation: NSLayoutRelation = .Equal, priority: UILayoutPriority = 1000) {
        center(.CenterY, relation: relation)
    }
    private func center(attribute: NSLayoutAttribute, value: Float = 0, relation: NSLayoutRelation, priority: UILayoutPriority =  1000) -> NSLayoutConstraint {
        let constraint = NSLayoutConstraint(item: self, attribute: attribute, relatedBy: relation, toItem: self.superview, attribute: attribute, multiplier: 1, constant: CGFloat(value))
        constraint.priority = priority
        return installConstraint(constraint)
    }
    
    /* Relation */
    func topOffset(toView: UIView, value: Float = 0, relation: NSLayoutRelation = .Equal, priority: UILayoutPriority =  1000) {
        relate(.Top, toView: toView, toAttribute: .Bottom, value: value, relation: relation, priority: priority)
    }
    func rightOffset(toView: UIView, value: Float = 0, relation: NSLayoutRelation = .Equal, priority: UILayoutPriority =  1000) {
        let (flippedValue, flippedRelation) = flip(value: value, relation: relation)
        relate(.Right, toView: toView, toAttribute: .Left, value: flippedValue, relation: flippedRelation, priority: priority)
    }
    func heightEqual(toView: UIView, relation: NSLayoutRelation = .Equal, priority: UILayoutPriority =  1000) {
        relate(.Height, toView: toView, toAttribute: .Height, relation: relation, priority: priority)
    }
    private func relate(attribute: NSLayoutAttribute, toView: UIView, toAttribute: NSLayoutAttribute, value: Float = 1, relation: NSLayoutRelation, priority: UILayoutPriority =  1000) {
        let constraint = NSLayoutConstraint(item: self, attribute: attribute, relatedBy: relation, toItem: toView, attribute: toAttribute, multiplier: 1, constant: CGFloat(value))
        constraint.priority = priority
        let installedConstraint = installConstraint(constraint)
    }


    /* Clean up */

    func removeAllConstraints() {
        for installedConstraint in relatedConstraints() {
            installedConstraint.active = false
        }
    }


    /* Private helpers */

    private func relatedConstraints() -> [NSLayoutConstraint] {
        
        var directConstraints = self.constraints() as [NSLayoutConstraint]
        if let indirectConstraints = relatedConstraintsInSuperViews(self) {
            directConstraints += indirectConstraints
        }
        return directConstraints
    }
    
    private func relatedConstraintsInSuperViews(view: UIView) -> [NSLayoutConstraint]? {
        return relatedConstraintsInSuperViews(view, relatedToView: view)
    }
    
    private func relatedConstraintsInSuperViews(view: UIView, relatedToView: UIView) -> [NSLayoutConstraint]? {
        
        if let superview = view.superview {
            
            var relatedConstraints = [NSLayoutConstraint]()
            for constraint in superview.relatedConstraints() {
                if let firstItem = constraint.firstItem as? UIView {
                    if firstItem == relatedToView {
                        relatedConstraints.append(constraint)
                    }
                } else {
                    if let secondItem = constraint.secondItem as? UIView {
                        if secondItem == relatedToView {
                            relatedConstraints.append(constraint)
                        }
                    }
                }
            }
            
            // Recursively add constraint in super view
            if let superRelatedConstraints = relatedConstraintsInSuperViews(superview, relatedToView: relatedToView) {
                for constraint in superRelatedConstraints {
                    relatedConstraints.append(constraint)
                }
            }
            
            if relatedConstraints.count > 0 {
                return relatedConstraints
            }
            return nil
        }
        return nil
    }

    private func installConstraint(constraint: NSLayoutConstraint) -> NSLayoutConstraint {
        if let installedConstraint = constraintSimilarToConstraint(constraint) {
            installedConstraint.constant = constraint.constant
            return installedConstraint
        } else {
            setTranslatesAutoresizingMaskIntoConstraints(false)
            constraint.active = true
            return constraint
        }
    }


    private func constraintSimilarToConstraint(constraint: NSLayoutConstraint) -> NSLayoutConstraint? {
        
        for installedConstraint in relatedConstraints() {
            let installedSecondItem = installedConstraint.secondItem as? UIView
            let secondItem = constraint.secondItem as? UIView
            if installedConstraint.firstAttribute == constraint.firstAttribute &&
                installedConstraint.relation == constraint.relation &&
                installedSecondItem == secondItem &&
                installedConstraint.secondAttribute == constraint.secondAttribute {
                return installedConstraint
            }
        }
        return nil
    }
    
    
    
    private func flip(#value: Float, relation: NSLayoutRelation) -> (flippedValue: Float, flippedRelation: NSLayoutRelation) {
        let flippedValue = -value
        let flippedRelation: NSLayoutRelation = {
            switch relation {
                case .GreaterThanOrEqual: return .LessThanOrEqual
                case .LessThanOrEqual: return .GreaterThanOrEqual
                default: return relation
            }
        }()
        return (flippedValue, flippedRelation)
    }
}