A modified version of Kickstarter's playground wrapper which is meant to simulate devices sizes in Xcode playgrounds. It will help with the design of UI elements in view controllers.

PlaygroundWrapper.swift

import UIKit

enum Device {
    case iPhoneSE
    case iPhone8
    case iPhone8Plus
    case iPhoneX
    case iPad
}

enum Orientation {
    case landscape
    case portrait
}

/**
 Creates a controller that represents a specific device, orientation with specific traits.

 - parameter child:            An optional controller to put inside the parent controller. If omitted
 a blank controller will be used.
 - parameter device:              The device the controller should represent.
 - parameter orientation:         The orientation of the device.
 - parameter contentSizeCategory: The content size category view controller should represent. 
 - parameter additionalTraits:    An optional set of traits that will also be applied. Traits in this collection
 will trump any traits derived from the device/orientation comboe specified.

 - returns: A root controller that can be set to the playground's live view with the content
 controller which should have UI elements added to it.
 */
func playgroundWrapper(child: UIViewController, device: Device = .iPhoneSE, orientation: Orientation = .portrait, contentSizeCategory: UIContentSizeCategory = .large, additionalTraits: UITraitCollection = .init()) -> UIViewController {
    
    let parent: UIViewController = UIViewController()
    parent.addChildViewController(child)
    
    let traits: UITraitCollection
    let parentSize: CGSize
    
    switch (device, orientation) {
    case (.iPhoneSE, .portrait):
        parentSize = .init(width: 320, height: 568)
        traits = .init(traitsFrom: [
            .init(horizontalSizeClass: .compact),
            .init(verticalSizeClass: .regular),
            .init(userInterfaceIdiom: .phone)
            ])
    case (.iPhoneSE, .landscape):
        parentSize = .init(width: 568, height: 320)
        traits = .init(traitsFrom: [
            .init(horizontalSizeClass: .regular),
            .init(verticalSizeClass: .compact),
            .init(userInterfaceIdiom: .phone)
            ])
    case (.iPhone8, .portrait):
        parentSize = .init(width: 375, height: 667)
        traits = .init(traitsFrom: [
            .init(horizontalSizeClass: .compact),
            .init(verticalSizeClass: .regular),
            .init(userInterfaceIdiom: .phone)
            ])
    case (.iPhone8, .landscape):
        parentSize = .init(width: 667, height: 375)
        traits = .init(traitsFrom: [
            .init(horizontalSizeClass: .regular),
            .init(verticalSizeClass: .compact),
            .init(userInterfaceIdiom: .phone)
            ])
    case (.iPhone8Plus, .portrait):
        parentSize = .init(width: 414, height: 736)
        traits = .init(traitsFrom: [
            .init(horizontalSizeClass: .compact),
            .init(verticalSizeClass: .regular),
            .init(userInterfaceIdiom: .phone)
            ])
    case (.iPhone8Plus, .landscape):
        parentSize = .init(width: 736, height: 414)
        traits = .init(traitsFrom: [
            .init(horizontalSizeClass: .regular),
            .init(verticalSizeClass: .compact),
            .init(userInterfaceIdiom: .phone)
            ])
    case (.iPhoneX, .portrait):
        parentSize = .init(width: 375, height: 812)
        traits = .init(traitsFrom: [
            .init(horizontalSizeClass: .compact),
            .init(verticalSizeClass: .regular),
            .init(userInterfaceIdiom: .phone)
            ])
    case (.iPhoneX, .landscape):
        parentSize = .init(width: 812, height: 375)
        traits = .init(traitsFrom: [
            .init(horizontalSizeClass: .regular),
            .init(verticalSizeClass: .compact),
            .init(userInterfaceIdiom: .phone)
            ])
    case (.iPad, .portrait):
        parentSize = .init(width: 768, height: 1024)
        traits = .init(traitsFrom: [
            .init(horizontalSizeClass: .regular),
            .init(verticalSizeClass: .regular),
            .init(userInterfaceIdiom: .pad)
            ])
    case (.iPad, .landscape):
        parentSize = .init(width: 1024, height: 768)
        traits = .init(traitsFrom: [
            .init(horizontalSizeClass: .regular),
            .init(verticalSizeClass: .regular),
            .init(userInterfaceIdiom: .pad)
            ])
    }
    
    let allTraits = UITraitCollection(traitsFrom: [
        traits,
        additionalTraits,
        .init(preferredContentSizeCategory: contentSizeCategory)
    ])
    parent.setOverrideTraitCollection(allTraits, forChildViewController: child)
    
    parent.view.addSubview(child.view)
    child.view.translatesAutoresizingMaskIntoConstraints = false
    
    parent.view.frame.size = parentSize
    parent.preferredContentSize = parentSize
    parent.view.backgroundColor = .white
    child.view.backgroundColor = .white
    
    parent.view.translatesAutoresizingMaskIntoConstraints = false
    NSLayoutConstraint.activate([
        child.view.leadingAnchor.constraint(equalTo: parent.view.leadingAnchor),
        child.view.trailingAnchor.constraint(equalTo: parent.view.trailingAnchor),
        child.view.topAnchor.constraint(equalTo: parent.view.topAnchor),
        child.view.bottomAnchor.constraint(equalTo: child.view.bottomAnchor)
    ])
    
    return parent
}