Async activity item. How to provide data to share after the activityController is presented and the activityType is selected.

AsyncActivityItemProvider.swift

import UIKit

/// Allows for asynchronously providing an item that will be shared
/// in an UIActivityViewController instance.
///
/// ### Usage: ###
/// ```
/// let activityItem = AsyncActivityItemProvider(placeholderItem: placeholderItem) { [weak self] (activityType, handler) in
///     // ⚠️ We're in a background thread.
///
///     // ⏱ Here is a good place to kick off any
///     //    progress indication.
///     self?.isInProgress = true
///
///     // 🔨 Perform the actions that will output
///     //    the item you want to share.
///     //    You can use the activityType parameter
///     //    if you care which option is selected.
///     SomeNetworkQuery(shareOption: activityType)
///         .request { result in
///             switch result {
///             case .success(let data):
///                 // ✅ When the work is done,
///                 //    call the handler with the result.
///                 handler(data)
///                 self?.isInProgress = false
///             case .failure(let error):
///                 {...}
///             }
///         }
///      }
///
/// // 💬 Show the share sheet.
/// let activityViewController = UIActivityViewController(activityItems: [activityItem], applicationActivities: nil)
/// present(activityViewController, animated: true, completion: nil)
///```
final class AsyncActivityItemProvider: UIActivityItemProvider {
    
    typealias ItemBuilder = (UIActivity.ActivityType?, (@escaping (Any) -> Void)) -> Void
    
    private var semaphore: DispatchSemaphore?
    private let itemBuilder: ItemBuilder
    
    init(placeholderItem: Any, itemBuilder: @escaping ItemBuilder) {
        self.itemBuilder = itemBuilder
        super.init(placeholderItem: placeholderItem)
    }
    
    override var item: Any {
        semaphore = DispatchSemaphore(value: 0)
        var result: Any?
        let handler: (Any) -> Void = { [weak self] itemValue in
            result = itemValue
            self?.semaphore?.signal()
        }
        itemBuilder(activityType, handler)
        
        // Block the thread for up to 5 seconds and cancel
        // in case of a timeout
        if semaphore?.wait(timeout: .now() + .seconds(5)) == .timedOut {
            cancel()
        }
        semaphore = nil
        return result ?? super.item
    }
    
}