How PlanGrid uses a Flux-Inspired Architecture to Simplify State Management

Benjamin Encz published an article about the architecture of PlanGrid.

They moved to a Flux-inspired “unidirectional flow” approach where state changes are performed in a Store (in the backend, if you will) and updates pushed to the user interface (the frontend). No ad-hoc view updates, no shortcuts. User events are emitted, handled by the store, and state updates affect the view. That’s it. So it’s always obvious how the user interface got into the state it’s in: all the details are plainly visible in the current state object.

Ben’s post is very deep and detailed. You’ll learn a ton from it:

  • architectural discussion: why “unidirection flow”, and why Flux?
  • setup of actions/events and the store type
  • basic state–view bindings via Reactive Cocoa
  • how testing stores (and views) is straightforward with this setup

I can’t wait for the next post in this series. Most of this easily applies to ReSwift, too, of course. And guess who just got inspired to refactor TableFlip so the model and view become even more loosely coupled?

5 Heuristics for "I have a complicated nested view controller setup. How do I handle passing data?"

That’s a recent question from the comments put in my own words. A view model that encapsulates the display state sounds promising at first. But when you don’t have a simple view that displays one thing, how do you model that in code? How do you model a sequence of view controllers, for example a more complex checkout process?

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ReSwift, Law of Demeter, and Another Level of Indirection

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Benjamin Encz’s presentation “Unidirectional Data Flow in Swift” about ReSwift features global app state: there’s one AppState type that acts as the facade to model and navigation state which is the single point of truth of every state in the app. This is a game changer when you suffer from massive view controller syndrome. In this post, I’d like to show you how he envisions the state of an app and what a next step could look like.

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Events as Declarative State

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I think I found something better than closures to handle events. Instead of dispatching closures that are themselves the changes that should be performed, simply declare the change.

enum Action {
    case ResizeBanana(BananaId, Size)
}

Now you need some kind of action handler, which Benjamin Encz calls “reducer” in his presentation “Unidirectional Data Flow in Swift”. Think of a list of reducers as a Chain of Responsibility only without the final consummation of the action. It is passed throughout the whole responder chain. Why reducer? Because they operate similar to the reduce function. The end result will be the combined result of all reducer’s mutations.

This is cool, because no component needs to know what such an action entails – none except the appropriate reducers.

If closures were great because where you type them you can see what is going on (more like “how” in my opinion), a simple action enum is even simpler, telling what should happen.

Works well with CQRS, I imagine. Will have to write a demo app using CQRS sometime to validate.

The current project is called ReSwift and code is available on GitHub.