Provident

Provident is a view controller provider framework that uses inversion of control to simplify view controller creation.

• Code that needs to create a view controller doesn't need to know how to create a view controller or what its dependencies are
• The view controller's internals (whether it uses storyboards, "vanilla" UIKit, SwiftUI etc) are hidden away, allowing a more declarative programming style
• Allows apps to avoid a common iOS coding trap where view controllers that present other view controllers (ad infinitum) need to know about all of the dependencies of those child view controllers
• Makes it a lot easier to introduce an architecture where dependencies and other services are loosely coupled from the rest of the system

Common Pitfalls with View Controller Creation Code

1) Different view controller "flavours" require flavour-specific initialisation code

• if using UIKit, the calling code needs to instantiate the view controller directly
• if using Storyboards, the calling code needs to use UIStoryboard to create the view controller
• if using SwiftUI, the calling code needs to wrap the View in a UIHostingController

If a view controller is reimplemented as a different "flavour" (e.g. refactored from a Storyboard to SwiftUI), all calling code must be changed accordingly. Essentially, some of the internals of the view controller are exposed, reducing encapsualtion.

Provident uses the concept of a ViewControllerProvider to solve this, moving all of the logic for view controller creation to a single place.

2) View controllers that create child view controllers need to know all of the dependencies of its children (and their children)

Assuming that your dependencies aren't static singletons, they'll need to be passed into the view controller during creation.

e.g. If we have a single RootViewController and construct it with RootViewController(dep1: Dependency1), as soon as that view controller is responsible for creating a ChildViewController with ChildViewController(dep2: Dependency2), we have to update all RootViewController initialisaton calls to RootViewController(dep1: Dependency1, dep2: Dependency2).

As RootViewController adds more child view controllers, and those child view controllers add their own child view controllers, the RootViewController suddenly has to be initialised with all dependencies used in all view controllers in the system, leading to the creation of "god objects".

Provident uses the concept of a Registry to solve this, allowing view controllers to be created without any knowledge of their dependencies.

3) View controllers that directly initialise child view controllers are inherantly coupled to their children

As we saw above, if we initialise ChildViewController(dep2: Dependency2) from within RootViewController, we tightly couple those implementations together, making it harder to switch out ChildViewController for another UIViewController instance.

The Provident Registry API works at the UIViewController level, allowing view controllers to be switched out without any changes to the calling code.