iOS 14：PHPickerViewController 有没有办法同时加载所有资源 PHPickerResult

Question

目前，我正在尝试深入研究 PHPickerViewController 以从照片中同时选择多个图像。所以我想要用户选择的图像数组，我尝试了太多方法但没有运气。这是我的代码，请告诉我有最佳实践吗？

func picker(_ picker: PHPickerViewController, didFinishPicking results: [PHPickerResult]) {
        picker.dismiss(animated: true, completion: nil)
        var images: [UIImage?] = []
        var totalConversionsCompleted = 0
        for (index,result) in results.enumerated() {
            result.itemProvider.loadObject(ofClass: UIImage.self, completionHandler: { (object, error) in
                let image = object as? UIImage
                images.append(image)
                totalConversionsCompleted += 1
                if totalConversionsCompleted == index {
                    print("completion happen \(images)")
                }
            })
        }
    }

Answer 1

我使用 single 让它工作DispatchGroup。这是我的委托方法实现：

func picker(_ picker: PHPickerViewController, didFinishPicking results: [PHPickerResult]) {
    picker.dismiss(animated: true) // dismiss a picker
    
    let imageItems = results
        .map { $0.itemProvider }
        .filter { $0.canLoadObject(ofClass: UIImage.self) } // filter for possible UIImages
    
    let dispatchGroup = DispatchGroup()
    var images = [UIImage]()
    
    for imageItem in imageItems {
        dispatchGroup.enter() // signal IN
        
        imageItem.loadObject(ofClass: UIImage.self) { image, _ in
            if let image = image as? UIImage {
                images.append(image)
            }
            dispatchGroup.leave() // signal OUT
        }
    }
    
    // This is called at the end; after all signals are matched (IN/OUT)
    dispatchGroup.notify(queue: .main) {
        print(images)
        // DO whatever you want with `images` array
    }
}