tejasmr / AutoLayoutConstraints

Library for auto layout constraints programmatically for UIKit views

AutoLayoutConstraints

CODE

import Foundation
import SwiftUI
import UIKit

struct AutoLayoutConstraints {
    // subView is view for which you want to add the ALC
    var subView: UIView
    // width constraint - in points or relative to the screenWidth = UIScreen.main.bounds.width
    var width: CGFloat
    // height constraint - in points or relative to the screenHeight = UIScreen.main.bounds.height
    var height: CGFloat
    // xOffset is the offset from either the left margin or right margin
    var xOffset: CGFloat = 0.0
    // yOffset is the offset from either the top margin or bottom margin
    var yOffset: CGFloat = 0.0
    // whether the subView should be centered horizontally
    var xCentered: Bool = true
    // whether the subview should be centered verically
    var yCentered: Bool = true
    // if this is true, the we offset it from the leading margin, else we do it from trailing margin
    var xLeading: Bool = true
    // if this is true, the we offset it from the top margin, else we do it from bottom margin
    var yTop: Bool = true
    
    func setAutoConstraints(_ viewController: UIViewController) {
        
        // I don't know what this does.
        subView.translatesAutoresizingMaskIntoConstraints = false
        
        let widthConstraint = NSLayoutConstraint(
           item: subView,
           attribute: NSLayoutConstraint.Attribute.width,
           relatedBy: NSLayoutConstraint.Relation.equal,
           toItem: nil,
           attribute: NSLayoutConstraint.Attribute.notAnAttribute,
           multiplier: 1,
            constant: width
        )
        let heightConstraint = NSLayoutConstraint(
           item: subView,
           attribute: NSLayoutConstraint.Attribute.height,
           relatedBy: NSLayoutConstraint.Relation.equal,
           toItem: nil,
           attribute: NSLayoutConstraint.Attribute.notAnAttribute,
           multiplier: 1,
            constant: height
        )
        var xConstraint = NSLayoutConstraint(
            item: subView,
            attribute: NSLayoutConstraint.Attribute.centerX,
            relatedBy: NSLayoutConstraint.Relation.equal,
            toItem: viewController.view,
            attribute: NSLayoutConstraint.Attribute.centerX,
            multiplier: 1,
            constant: 0
        )
        var yConstraint = NSLayoutConstraint(
            item: subView,
            attribute: NSLayoutConstraint.Attribute.centerY,
            relatedBy: NSLayoutConstraint.Relation.equal,
            toItem: viewController.view,
            attribute: NSLayoutConstraint.Attribute.centerY,
            multiplier: 1,
            constant: 0
        )
        if !xCentered {
            if xLeading {
                xConstraint = NSLayoutConstraint(
                   item: subView,
                   attribute: NSLayoutConstraint.Attribute.leading,
                   relatedBy: NSLayoutConstraint.Relation.equal,
                   toItem: viewController.view,
                   attribute: NSLayoutConstraint.Attribute.leadingMargin,
                   multiplier: 1.0,
                    constant: xOffset
                )
            }
            else {
                xConstraint = NSLayoutConstraint(
                   item: subView,
                   attribute: NSLayoutConstraint.Attribute.trailing,
                   relatedBy: NSLayoutConstraint.Relation.equal,
                   toItem: viewController.view,
                   attribute: NSLayoutConstraint.Attribute.trailingMargin,
                   multiplier: 1.0,
                    constant: -xOffset
                )
            }
        }
        if !yCentered {
            if yTop {
                yConstraint = NSLayoutConstraint(
                    item: subView,
                    attribute: NSLayoutConstraint.Attribute.top,
                    relatedBy: NSLayoutConstraint.Relation.equal,
                    toItem: viewController.view,
                    attribute: NSLayoutConstraint.Attribute.topMargin,
                    multiplier: 1.0,
                    constant: yOffset
                )
            }
            else {
                yConstraint = NSLayoutConstraint(
                    item: subView,
                    attribute: NSLayoutConstraint.Attribute.bottom,
                    relatedBy: NSLayoutConstraint.Relation.equal,
                    toItem: viewController.view,
                    attribute: NSLayoutConstraint.Attribute.bottomMargin,
                    multiplier: 1.0,
                    constant: -yOffset
                )
            }
        }
        viewController.view.addConstraints(
                [widthConstraint, heightConstraint, xConstraint, yConstraint]
        )
    }
}

Usage (under construction)

Some supporting variables for the following examples

// width of the screen
let screenWidth = UIScreen.main.bounds.width
let screenHeight = UIScreen.main.bounds.height
let label = UILabel()

If you want a UI Component at the center of the screen

// Inside UIViewController, in some function like override func viewDidLoad()
let labelALC = AutoLayoutConstraints(subView: label, width: screenWidth / 2, height: screenHeight / 4")
labelALC.setConstraints(self)

Let us unpack the first statement.

subView: label -> sets the subView property of the AutoLayoutConstraints object as the UILabel named label

width: screenWidth / 2 -> sets the width property of the AutoLayoutConstraints object as half of the screenWidth

height: screenHeight / 4 -> sets the height property of the AutoLayoutConstraints object as quater of the screenHeight

In the second statement.

We pass the UIViewController as the parameter, so the constraints will be added to the view property of the viewController.

The assumptions made here are:

1. The subView is centered vertically.

2. The subView is centered horizontally.