应用扩展概览

// Extensions run in their own process, launched
// by the host (Photos, Safari, Messages, the system),
// not by your main app.

import Foundation
// Container app + Extension target share data via
// an App Group, e.g. group.com.example.app
let group = "group.com.example.app"
_ = group

import Foundation
// Share extension reads incoming items:
// extensionContext?.inputItems
//   each NSExtensionItem has attachments (NSItemProvider)
let share = "appears in the share sheet"
_ = share

import UniformTypeIdentifiers
func handle(_ provider: NSItemProvider) {
    if provider.hasItemConformingToTypeIdentifier(
        UTType.url.identifier) {
        provider.loadItem(
            forTypeIdentifier: UTType.url.identifier) {
            value, _ in
            print("shared url:", value ?? "none")
        }
    }
}

import Foundation
// Action extension may return modified items:
// extensionContext?.completeRequest(
//     returningItems: outputItems)
let action = "acts on content, can return a result"
_ = action

import UserNotifications
// Override in UNNotificationServiceExtension:
// didReceive(_ request:, withContentHandler:)
//   mutate bestAttemptContent, then call the handler
let service = "modifies push before it shows"
_ = service

import UserNotifications
// UNNotificationContentExtension renders a custom view
// for a given UNNotificationCategory when expanded.
let content = "custom expanded notification UI"
_ = content

import Foundation
func finish(context: NSExtensionContext?) {
    context?.completeRequest(
        returningItems: [], completionHandler: nil)
}

// Info.plist of an extension declares its point:
// NSExtension > NSExtensionPointIdentifier
//   e.g. com.apple.share-services
//        com.apple.usernotifications.service
let point = "each extension declares its point"
_ = point

import Foundation
// Tight memory + short runtime.
// Pattern: extension stages data in the App Group,
// the main app processes it fully on next launch.
let limits = "keep extensions lean and fast"
_ = limits

import Foundation
// Shared Swift package 'AppCore' linked by:
//   - main app target
//   - share extension target
//   - widget extension target
let shared = "one source of truth for models"
_ = shared