alisoftware / functionalvcdemo

Demo for the Functional ViewControllers concept in RxSwift

FunctionalVCDemo

This project is a sample app demonstrating the concept of Functional ViewControllers using RxSwift.

Concept

A Functional ViewController is a ViewController that can be used as a function func show(input: T) -> Observable<U>. It will display the ViewController to gather data from the user, wait for the user to validate, then emit a .next even on the returned Observable<U> once validated.

Advantages

This pattern is useful to integrate a ViewContoller is a functional workflow, abstracting away the fact that the ViewController is a UI component and instead treating it as an asynchronous function getting inputs and asynchronously returning an output.

Concept example

Imagine you have some Functional VCs that can be exposed in those functions:

• func pickImage() -> Observable<UIImage>
• func askTitle() -> Observable<String>
• func askNote() -> Observable<Int>

Each function presents a UIViewController, waits for the user to interact and validate (e.g. pickImage will present an UIImagePickerController and wait for the user to select an image), and asynchronously return the result (in case of pickImage, that's the UIImage obvously).

With this you can easily chain those functional VCs usng classic RxSwift reactive chains:

struct ImageDescription {
  let image: UIImage?
  let name: String?
  let note: Int?
}

var imageDesc: ImageDescription()
self.pickImage()
  .flatMap({ image in
    imageDesc.image = image
    self.askTitle()
  })
  .flatMap({ title in
    imageDesc.title = title
    self.askNote()
  })
  .subscribe(onNext: { note in
    imageDesc.note = note
    print(imageDesc)
  })
  .addDisposableTo(disposeBag)

This allows to read the workflow like a chain of steps happening one after the other, hiding away the complexity of asynchronicity.