Axiom Photo Library

Signs you're making this harder than it needs to be:

• ❌ Using UIImagePickerController (deprecated for photo selection)
• ❌ Requesting full library access when picker suffices (privacy violation)
• ❌ Ignoring .limited authorization status (users can't expand selection)
• ❌ Not handling Transferable loading failures (crashes on large photos)
• ❌ Synchronously loading images from picker results (blocks UI)
• ❌ Using PhotoKit APIs when you only need to pick photos (over-engineering)
• ❌ Assuming .authorized after user grants access (could be .limited)

Mandatory First Steps

Before implementing photo library features:

1. Choose Your Approach

What do you need?

┌─ User picks photos (no library browsing)?
│  ├─ SwiftUI app → PhotosPicker (iOS 16+)
│  └─ UIKit app → PHPickerViewController (iOS 14+)
│  └─ NO library permission needed! Picker handles it.
│
├─ Display user's full photo library (gallery UI)?
│  └─ Requires PHPhotoLibrary authorization
│     └─ Request .readWrite for browsing
│     └─ Handle .limited status with presentLimitedLibraryPicker
│
├─ Save photos to camera roll?
│  └─ Requires PHPhotoLibrary authorization
│     └─ Request .addOnly (minimal) or .readWrite
│
└─ Just capture with camera?
   └─ Don't use PhotoKit - see camera-capture skill

2. Understand Permission Levels

Key insight: PHPicker and PhotosPicker require NO permission. The system handles privacy.

3. Info.plist Keys

<!-- Required for any PhotoKit access -->
<key>NSPhotoLibraryUsageDescription</key>
<string>Access your photos to share them</string>

<!-- Required if saving photos -->
<key>NSPhotoLibraryAddUsageDescription</key>
<string>Save photos to your library</string>

Core Patterns

Pattern 1: SwiftUI PhotosPicker (iOS 16+)

Use case: Let users select photos in a SwiftUI app.

import SwiftUI
import PhotosUI

struct ContentView: View {
    @State private var selectedItem: PhotosPickerItem?
    @State private var selectedImage: Image?

    var body: some View {
        VStack {
            PhotosPicker(
                selection: $selectedItem,
                matching: .images  // Filter to images only
            ) {
                Label("Select Photo", systemImage: "photo")
            }

            if let image = selectedImage {
                image
                    .resizable()
                    .scaledToFit()
            }
        }
        .onChange(of: selectedItem) { _, newItem in
            Task {
                await loadImage(from: newItem)
            }
        }
    }

    private func loadImage(from item: PhotosPickerItem?) async {
        guard let item else {
            selectedImage = nil
            return
        }

        // Load as Data first (more reliable than Image)
        if let data = try? await item.loadTransferable(type: Data.self),
           let uiImage = UIImage(data: data) {
            selectedImage = Image(uiImage: uiImage)
        }
    }
}

Multi-selection:

@State private var selectedItems: [PhotosPickerItem] = []

PhotosPicker(
    selection: $selectedItems,
    maxSelectionCount: 5,
    matching: .images
) {
    Text("Select Photos")
}

Advanced Filters (iOS 15+/16+)

// Screenshots only