Diffable Data Source Sample

A small iOS sample app demonstrating UICollectionViewDiffableDataSource with a compositional layout and a simple MVVM flow. It fetches adoptable animals from the Petfinder API and shows main / loading / error states using distinct collection view sections.

Features

• UICollectionView with UICollectionViewCompositionalLayout
• UICollectionViewDiffableDataSource to manage items and sections
• MVVM-style AnimalsViewModel that handles paging and load-more
• Dedicated cells for animals, loading shimmer, and error + retry
• Pull-to-refresh and infinite scroll (load more when last cell appears)
• Simple image loading for animal photos

Stack

• Language: Swift
• Platform: iOS (Xcode project included)
• Notable APIs / patterns: UICollectionViewDiffableDataSource, UICollectionViewCompositionalLayout, async/await networking

Repo layout

How it fits together:

• ViewController owns the collection view and the diffable data source. It asks AnimalsViewModel to fetch data and reacts to callbacks to update snapshots.
• AnimalsViewModel performs network calls through NetworkService and exposes simple closures for UI updates (onFetchStarted, onAnimalsUpdated, onError, onLoadMoreStarted).
• NetworkService decodes Petfinder responses into local Animal models used by the UI.

Quick start (run locally)

1. Clone the repo:

git clone https://github.com/mauricetinn/diffable-data-source-sample.git cd diffable-data-source-sample

2. Open the Xcode project:

• Double-click diffableDataSourceSample.xcodeproj or run:

  open diffableDataSourceSample/diffableDataSourceSample.xcodeproj
  

3. Configure the Petfinder API token (see Security note below).
4. Select a Simulator or device and run (Cmd+R).

There are no external dependencies or package managers required — just Xcode.

Configuration / API token

This project currently contains a hardcoded access token inside NetworkService.swift. Replace this with a safe configuration before shipping or publishing the repo.

Recommended approaches:

• Use environment variables in the Xcode run scheme:
• Edit Scheme → Run → Arguments → Environment Variables → add PETFINDER_TOKEN=your_token
• Then in NetworkService, read the token at runtime:

private let accessToken = ProcessInfo.processInfo.environment["PETFINDER_TOKEN"] ?? ""

• Or store a key in Info.plist (less secure) and read it with Bundle.main.infoDictionary?["PETFINDER_TOKEN"] as? String.

You must obtain a Petfinder access token from https://www.petfinder.com/developers/ and set it before running requests.

Known TODOs / Improvements

• Add cell selection handling (tap to show detail).
• Extract image loading to a dedicated caching image loader (e.g., use URLCache or a library).
• Make sections more flexible (separate section types and supplementary views).
• Improve error handling and show more descriptive UI for different failure types.
• Replace hardcoded token with secure storage / secrets manager.

Note: There is a TODO comment in ViewController.swift listing items such as delegate handling, dynamic cell heights, more sections, handling of negative cases, loading state and tap actions.

Important security note

A token-like string is present in NetworkService.swift. Treat it as sensitive — rotate it now if that credential is real, and remove it from the repository history. Use environment variables or other secure configuration methods instead of committing secrets.

Contributing

• Open an issue or submit a PR with improvements (image caching, decoupling network code, tests, etc.).
• Keep changes focused and add short descriptions for behavior changes.

License

No license file present. Add a LICENSE if you want to open-source this project.

Questions you might ask next

• How can I add image caching to avoid re-downloading images when scrolling?
• Where should I put unit tests for AnimalsViewModel to mock the NetworkService?
• How can I adapt the compositional layout to support a detail view with a larger single-column section?