附加元素后的空数组答案

【问题标题】：Empty array after appended element附加元素后的空数组
【发布时间】：2021-09-11 16:47:23
【问题描述】：

我正在尝试从导航栏上的 UIAlertController 将图像上传到 UICollectionView。集合视图位于另一个页面上。

我使用允许多张照片选择的 BSImagePicker 3rd 方库。

selectImages() 函数实际上将照片附加到 selectedImages 数组并在调试器上打印出来

import Photos
import BSImagePicker

class CustomFeedNavigationBar: UIView {

    static let height: CGFloat = 48
    var collectionView = NewPostImagesViewController().collectionView
    var selectedImages: [UIImage] = []

    var rootVC = UIApplication.shared.keyWindow?.rootViewController
    unowned var navigationController: UINavigationController

    init(navigationController: UINavigationController) {
        self.navigationController = navigationController
        super.init(frame: .zero)

        translatesAutoresizingMaskIntoConstraints = false

        addSubview(addPostButton)
    }

    lazy var addPostButton: UIButton = {
        let button = UIButton(type: .custom)
        button.setImage(UIImage(named: "addPost"), for: .normal)
        button.imageView?.contentMode = .scaleAspectFit
        button.addTarget(self, action: #selector(handleAdd), for: .touchUpInside)
        button.translatesAutoresizingMaskIntoConstraints = false
        return button
    }()

    @objc func handleAdd() {
        let actionSheet = UIAlertController(title: "Add post", message: nil, preferredStyle: .actionSheet)

        actionSheet.addAction(UIAlertAction(title: "Dismiss", style: .cancel, handler: { action in
            print("tap dismiss")
        }))
        actionSheet.addAction(UIAlertAction(title: "Camera", style: .default, handler: { action in
            print("tap camera")
        }))
        actionSheet.addAction(UIAlertAction(title: "Gallery", style: .default, handler: { action in

            self.selectImages()

            let viewController = NewPostImagesViewController()
            viewController.hidesBottomBarWhenPushed = true
            self.navigationController.pushViewController(viewController, animated: true)
        }))

        rootVC?.present(actionSheet, animated: true, completion: nil)
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

}

extension CustomFeedNavigationBar {

    func selectImages() {
        let imagePicker = ImagePickerController()
        rootVC?.presentImagePicker(imagePicker, select: { (asset) in
        }, deselect: { (asset) in

        }, cancel: { (assets) in

        }, finish: { (assets) in

            self.selectedImages = []
            let options: PHImageRequestOptions = PHImageRequestOptions()
            options.deliveryMode = .highQualityFormat

            for asset in assets {
                PHImageManager.default().requestImage(for: asset, targetSize: PHImageManagerMaximumSize,
                                                      contentMode: .aspectFit, options: options) { (image, info) in
                    self.selectedImages.append(image!)
                    print("images appended? \(self.selectedImages) YES") // selectedImages array appended elements
                    self.collectionView.reloadData()
                }
            }
        })
    }
}

但是当我点击下一步并转到下一页时，数组是空的！它在调试器上什么也没有显示

class NewPostImagesViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // ...
        // Loaded collection view and etc.

        print("images loaded? \(CustomFeedNavigationBar(navigationController: navigationController!).selectedImages)") // selectedImages array is empty again
    }
}

这是调试器输出：

images not appended []
images appended? [<UIImage:0x6000030cad00 anonymous {1668, 2500}>] YES
images appended? [<UIImage:0x6000030cad00 anonymous {1668, 2500}>, <UIImage:0x6000030cdf80 anonymous {4288, 2848}>] YES

【问题讨论】：

您正在打印中新建一个 CustomFeedNavigationBar 实例
@Shadowrun 我只是将 CustomFeedNavigationBar 添加到打印中，只是为了访问 selectedImages 属性。有什么更好的方法？
不，您添加了“a”（新）CustomFeedNavigationBar，而不是“the”CustomFeedNavigationBar（您已经拥有），这就是数组为空的原因。

标签： ios arrays swift uicollectionview cocoapods

【解决方案1】：

这里

print("images loaded? \(CustomFeedNavigationBar(navigationController: navigationController!).selectedImages)") // selectedImages array is empty again

您创建了一个新实例而不是具有图像的实例，因此请尝试：

class NewPostImagesViewController: UIViewController {
    var selectedImages = [UIImage]()

actionSheet.addAction(UIAlertAction(title: "Gallery", style: .default, handler: { action in

    self.selectImages()

}))

let g = DispatchGroup()
for asset in assets {
    g.enter()
    PHImageManager.default().requestImage(for: asset, targetSize: PHImageManagerMaximumSize,
                                          contentMode: .aspectFit, options: options) { (image, info) in
        self.selectedImages.append(image!)
        print("images appended? \(self.selectedImages) YES") // selectedImages array appended elements
        self.collectionView.reloadData() 
        g.leave()
    }
}

g.notify(queue:.main) {
   let viewController = NewPostImagesViewController()
   viewController.hidesBottomBarWhenPushed = true
   viewController.selectedImages = selectedImages 
self.navigationController.pushViewController(viewController, animated: true)
}

【讨论】：