UIView+Pin.swift

UIView+Pin.swift

//
//  Copyright (c) Microsoft Corporation. All rights reserved.
//

import Foundation
import UIKit

// A small utility for NSLayoutDimension shortcuts, easily reduce lots of auto layout codes.

public protocol PinObject {
  var topAnchor: NSLayoutYAxisAnchor { get }
  var bottomAnchor: NSLayoutYAxisAnchor { get }
  var leadingAnchor: NSLayoutXAxisAnchor { get }
  var trailingAnchor: NSLayoutXAxisAnchor { get }
}

extension UIView: PinObject {}
extension UILayoutGuide: PinObject {}

public extension UIView {

  struct PinOptions: OptionSet {

    public let rawValue: Int

    public static let all: PinOptions = [.top, .trailing, .bottom, .leading]

    public static let top = PinOptions(rawValue: 1 << 0)
    public static let trailing = PinOptions(rawValue: 1 << 1)
    public static let bottom = PinOptions(rawValue: 1 << 2)
    public static let leading = PinOptions(rawValue: 1 << 3)

    public init(rawValue: Int) {
      self.rawValue = rawValue
    }
  }

  /// Add layout constraints. Also sets translatesAutoresizingMaskIntoConstraints to false.
  ///
  /// - Parameters:
  ///   - pinObject: The pinObject that this view is pined to. Maybe a UIView or an UILayoutGuideObject
  ///   - edges: Choose which edge to pin
  func pin(to pinObject: PinObject, edges: PinOptions, priority: UILayoutPriority) {
    translatesAutoresizingMaskIntoConstraints = false

    var constraints = [NSLayoutConstraint]()
    if edges.contains(.leading) {
      constraints.append(leadingAnchor.constraint(equalTo: pinObject.leadingAnchor))
    }

    if edges.contains(.trailing) {
      constraints.append(trailingAnchor.constraint(equalTo: pinObject.trailingAnchor))
    }

    if edges.contains(.top) {
      constraints.append(topAnchor.constraint(equalTo: pinObject.topAnchor))
    }

    if edges.contains(.bottom) {
      constraints.append(bottomAnchor.constraint(equalTo: pinObject.bottomAnchor))
    }

    constraints.forEach { $0.priority = priority }

    if !constraints.isEmpty {
      NSLayoutConstraint.activate(constraints)
    }
  }

  /// Pin to parentView edges
  func pinEdges(to parentView: UIView, edges: PinOptions = .all, priority: UILayoutPriority = .required) {
    pin(to: parentView, edges: edges, priority: priority)
  }

  /// Pin to parentView layoutMarginsGuide
  func pinToMargins(of parentView: UIView, edges: PinOptions = .all, priority: UILayoutPriority = .required) {
    pin(to: parentView.layoutMarginsGuide, edges: edges, priority: priority)
  }

  /// Pin to parentView safeAreaLayoutGuide
  func pinToSafeArea(of parentView: UIView, edges: PinOptions = .all, priority: UILayoutPriority = .required) {
    pin(to: parentView.safeAreaLayoutGuide, edges: edges, priority: priority)
  }

  func pinToEdges(of parentView: UIView, insets: UIEdgeInsets, edges: PinOptions = .all, priority: UILayoutPriority = .required) {
    translatesAutoresizingMaskIntoConstraints = false
    
    var constraints = [NSLayoutConstraint]()
    if edges.contains(.leading) {
        constraints.append(leadingAnchor.constraint(equalTo: parentView.leadingAnchor, constant: insets.left))
    }
    if edges.contains(.trailing) {
        constraints.append(trailingAnchor.constraint(equalTo: parentView.trailingAnchor, constant: -insets.right))
    }
    if edges.contains(.top) {
        constraints.append(topAnchor.constraint(equalTo: parentView.topAnchor, constant: insets.top))
    }
    if edges.contains(.bottom) {
        constraints.append(bottomAnchor.constraint(equalTo: parentView.bottomAnchor, constant: -insets.bottom))
    }
    
    constraints.forEach { $0.priority = priority }
    NSLayoutConstraint.activate(constraints)
  }
}

public extension UILayoutPriority {
    static var almostRequired: UILayoutPriority {
        return .required - 1
    }
}