Did you know that there is a function in the Objective-C runtime that gives you exactly this list of classes in your app? With this tool, you can easily build a debug view which will enable you to instantiate any of your ViewControllers, and save you a lot of development time.

1. How to build a debug view
(almost) for free
Vincent Pradeilles (@v_pradeilles) & Benoît Caron – Worldline !

2. Why?

3. Why?
You have to make sure an app displays properly on the iPhone X, but:
• Data is driven by web-services
• No mocks are available
• More than 150 different screens
• Some screens are part of complex business scenarios

4. What would be the right tool?

5. A debug view!
• Lists all available UIViewControllers
• Indicate a specific use case, if
needed
• Instantiates, then pushes or
presents the controller

6. How do we get the data?

7. Objective-C

8. import ObjectiveC

9. The ObjectiveC module
• Exposes C APIs to interact with the ObjectiveC runtime
• Perfectly OK to use it with Swift

10. The ObjectiveC module
func objc_copyClassNamesForImage(_ image: UnsafePointer<Int8>,
_ outCount: UnsafeMutablePointer<UInt32>?)
-> UnsafeMutablePointer<UnsafePointer<Int8>>?
• This function returns a list of all the classes defined in a given bundle
• That’s all the data you’ll ever need to build a basic debug view!

11. How to use it?
extension Bundle {
func retrieveAllViewControllers() -> [String] {
guard let bundlePath = self.executablePath else { return [] }
var viewControllers = [String]()
var size: UInt32 = 0
let classes = objc_copyClassNamesForImage(bundlePath, &size)
for index in 0..<size {
if let className = classes?[Int(index)],
let name = NSString.init(utf8String:className) as String?,
NSClassFromString(name) is UIViewController.Type
{
viewControllers.append(name)
}
}
return viewControllers
}
}

12. How to use it?
extension Bundle {
func retrieveAllViewControllers() -> [String] {
guard let bundlePath = self.executablePath else { return [] }
var viewControllers = [String]()
var size: UInt32 = 0
let classes = objc_copyClassNamesForImage(bundlePath, &size)
for index in 0..<size {
if let className = classes?[Int(index)],
let name = NSString.init(utf8String:className) as String?,
NSClassFromString(name) is UIViewController.Type
{
viewControllers.append(name)
}
}
return viewControllers
}
}

13. How to use it?
extension Bundle {
func retrieveAllViewControllers() -> [String] {
guard let bundlePath = self.executablePath else { return [] }
var viewControllers = [String]()
var size: UInt32 = 0
let classes = objc_copyClassNamesForImage(bundlePath, &size)
for index in 0..<size {
if let className = classes?[Int(index)],
let name = NSString.init(utf8String:className) as String?,
NSClassFromString(name) is UIViewController.Type
{
viewControllers.append(name)
}
}
return viewControllers
}
}

14. How to use it?
extension Bundle {
func retrieveAllViewControllers() -> [String] {
guard let bundlePath = self.executablePath else { return [] }
var viewControllers = [String]()
var size: UInt32 = 0
let classes = objc_copyClassNamesForImage(bundlePath, &size)
for index in 0..<size {
if let className = classes?[Int(index)],
let name = NSString.init(utf8String:className) as String?,
NSClassFromString(name) is UIViewController.Type
{
viewControllers.append(name)
}
}
return viewControllers
}
}

15. How to use it?
extension Bundle {
func retrieveAllViewControllers() -> [String] {
guard let bundlePath = self.executablePath else { return [] }
var viewControllers = [String]()
var size: UInt32 = 0
let classes = objc_copyClassNamesForImage(bundlePath, &size)
for index in 0..<size {
if let className = classes?[Int(index)],
let name = NSString.init(utf8String:className) as String?,
NSClassFromString(name) is UIViewController.Type
{
viewControllers.append(name)
}
}
return viewControllers
}
}

16. How to use it?
extension Bundle {
func retrieveAllViewControllers() -> [String] {
guard let bundlePath = self.executablePath else { return [] }
var viewControllers = [String]()
var size: UInt32 = 0
let classes = objc_copyClassNamesForImage(bundlePath, &size)
for index in 0..<size {
if let className = classes?[Int(index)],
let name = NSString.init(utf8String:className) as String?,
NSClassFromString(name) is UIViewController.Type
{
viewControllers.append(name)
}
}
return viewControllers
}
}

17. How to use it?
extension Bundle {
func retrieveAllViewControllers() -> [String] {
guard let bundlePath = self.executablePath else { return [] }
var viewControllers = [String]()
var size: UInt32 = 0
let classes = objc_copyClassNamesForImage(bundlePath, &size)
for index in 0..<size {
if let className = classes?[Int(index)],
let name = NSString.init(utf8String:className) as String?,
NSClassFromString(name) is UIViewController.Type
{
viewControllers.append(name)
}
}
return viewControllers
}
}

18. How to use it?
extension Bundle {
func retrieveAllViewControllers() -> [String] {
guard let bundlePath = self.executablePath else { return [] }
var viewControllers = [String]()
var size: UInt32 = 0
let classes = objc_copyClassNamesForImage(bundlePath, &size)
for index in 0..<size {
if let className = classes?[Int(index)],
let name = NSString.init(utf8String:className) as String?,
NSClassFromString(name) is UIViewController.Type
{
viewControllers.append(name)
}
}
return viewControllers
}
}

19. How to use it?
extension Bundle {
func retrieveAllViewControllers() -> [String] {
guard let bundlePath = self.executablePath else { return [] }
var viewControllers = [String]()
var size: UInt32 = 0
let classes = objc_copyClassNamesForImage(bundlePath, &size)
for index in 0..<size {
if let className = classes?[Int(index)],
let name = NSString.init(utf8String:className) as String?,
NSClassFromString(name) is UIViewController.Type
{
viewControllers.append(name)
}
}
return viewControllers
}
}

20. How to use it?
func instantiateController(named name: String) -> UIViewController? {
let controllerClass = NSClassFromString(name) as? UIViewController.Type
return controllerClass?.init()
}

21. That’s it!

23. 🎉

24. We’ve just seen the « free » part…

25. …let’s look at the « almost » side of things

26. Providing Initial Data
@objc public protocol DebugViewCompliant {
func prepareForDebugView()
}
extension MyViewController: DebugViewCompliant {
func prepareForDebugView() {
// do some configuration
}
}

27. Handling Use Cases
@objc public protocol DebugViewUseCaseCompliant {
static func getUseCases() -> [String]
func prepareForDebugView(useCase: String)
}
extension MyViewController: DebugViewUseCaseCompliant {
static func getUseCases() -> [String] {
return ["User Not Logged", "User Logged In"]
}
func prepareForDebugView(useCase: String) {
// do some configuration according to `useCase`
}
}

28. Working with Storyboards
@objc public protocol DebugViewInstantiable {
static func initForDebugView() -> UIViewController
}
extension MyViewController: DebugViewInstantiable {
static func initForDebugView() -> UIViewController {
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let viewController =
storyboard.instantiateViewController("MyViewController") as!
MyViewController
return viewController
}
}

29. Does it work on a real project?

30. Does it work on a real project?
YES!

31. How can I use it?

32. How can I use it?
• Available on Github : https://github.com/worldline/ControllerFactory
• Works with CocoaPods and Carthage
• You just need to call:
ControllerFactory.instantiate(bundle: Bundle.main)
• Only one limitation: it does not work with generic classes 😕

33. 😊

34. See you tomorrow!