Swiftui Core Data With Model Save

Intro

TL;DR; Demo/test project showcasing easier to maintain Core Data processing in SwiftUI applications by abstracting Core Data processing away from the UI and into its own App Model.

Why

Good SW engineering practice seeks to achieve a Separation of Concerns. As of 10th of August 2020, the 'normal' SwiftUI approach to integration of Core Data involves data operations (using @FetchRequest and Core Data's Managed Object Context) within the immediate hierarchy of the View components that consume and create that same data.

As convenient as it is to work with initially (particularly @FetchRequest) - splattering Core Data and associated processing throughout an application's UI components disobeys the Separation of Concerns and is liable to result in apps that are difficult maintain.

What's demonstrated

Alongside the conventional @FetchRequest/MOC approach for comparison, this project demonstrates how Core Data can be handled within an app's model, thereby separating data and UI concerns, while still maintaining ease of use.

• Alternative model based Core Data integration that:
  1. Keeps data synchronised across the views using a Combinepublisher for the Core Data results.
  2. Is almost as convenient to work with as @FetchRequest
• A conventional @FetchRequest Core Data integration for comparison.
• How to setup Core Data using Xcode 12 and its SwiftUI App Life Cycle template I.e. without an AppDelegate.swift and SceneDelegate.swift to setup the Core Data persistentContainer, but with a model and the the usage of @StateObject to do the same.
• Use of the iOS14/SwiftUI's @StateObject, @Environment, @EnvironmentObject, @ObservedObject and @FetchRequest property wrappers.

Installation

This project requires at least iOS14 and Xcode 12 (I used Xcode 12.0 beta 4)

Running/testing

Should run on any iOS 14+ simulator or device.

When it runs, the app will display summary data about the number of Item entities it has in the system in various View components.

Components are named after how they get their data, I.e. either from:

1. The Model
2. Or by using the 'normal' @FetchRequest and MOC approach

When normal and flagged Items are Added, the data across all of the View components should remain the same.

Notes

1. The code contains copious comments and should be pretty self explanatory.
2. Kudos and thanks to Apostolos Giokas for his excellent article on Medium that contained the Core Data Combine publisher class implementation.