为什么我的图像没有出现在 UIImage 视图中？

Question

我做了一个视图控制器来显示一个图像，图像将在用户按下checkOutVC 中的右键项目后显示，就像这样

图片应该像这样出现在ReusableImageDisplayVC中

我将图像从checkOutVC 发送到ReusableImageDisplayVC，我用于这些视图控制器的代码如下：

class CheckoutTVC: UITableViewController {

 @IBAction func openImageBarButtonDidPressed(_ sender: Any) {

        var displayedImage = UIImage()
        let imagePath = "https://***.jpg"
        let urlImage = URL(string: imagePath)

        NetworkingService.fetchData(url: urlImage!) { (result) in
            self.activityIndicator.startAnimating()

            switch result {
            case .failure(let error) :
                self.activityIndicator.stopAnimating()
                self.showAlert(alertTitle: "Sorry", alertMessage: error.localizedDescription, actionTitle: "Back")
            case .success (let imageData):
                self.activityIndicator.stopAnimating()
                displayedImage = UIImage(data: imageData)!
            }
        }


        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let popup = storyboard.instantiateViewController(withIdentifier: "imageDisplay") as! ReusableImageDisplayVC
        popup.photo = displayedImage


        present(popup, animated: true, completion: nil)

    }
}

ReusableImageDisplayVC 中的代码如下

class ReusableImageDisplayVC: UIViewController {

    @IBOutlet weak var ImagePhoto: UIImageView!
    var photo : UIImage?

    override func viewDidLoad() {
        super.viewDidLoad()

        if photo == nil {
            print("photo is nil")
        } else {
            print("photo is not nil")
        }

        print(photo!)

        ImagePhoto.image = photo!


        let tapGesture = UITapGestureRecognizer(target: self, action: #selector(ReusableImageDisplayVC.tapFunction(sender:)))
        tapGesture.numberOfTapsRequired = 1
        ImagePhoto.addGestureRecognizer(tapGesture)
        view.addGestureRecognizer(tapGesture)

    }



    @objc func tapFunction(sender: UITapGestureRecognizer) {
        dismiss(animated: true, completion: nil)
    }


}

正如我们在ReusableImageDisplayVC 中看到的那样，我正在尝试确保以前 VC 中的 UIImage 可用，并在调试区域中打印出来

照片不是零， UIImage: 0x6040008bde20, {0, 0}

我也分配给了ImageViewImagePhoto.image = photo!

但是为什么当我运行应用程序时，它没有出现？

但是如果我像下面的代码那样直接在 ReusableImageDisplayVC 中硬编码下载图像的过程，图像就会出现

class ReusableImageDisplayVC: UIViewController {

    @IBOutlet weak var ImagePhoto: UIImageView!
    var photo : UIImage?
    var something : String?

    override func viewDidLoad() {
        super.viewDidLoad()

        let imagePath = "https://***.jpg"
        let urlImage = URL(string: imagePath)

        NetworkingService.fetchData(url: urlImage!) { (result) in

            switch result {
            case .failure(let error) :
                self.showAlert(alertTitle: "Sorry", alertMessage: error.localizedDescription, actionTitle: "Back")
            case .success (let imageData):
               self.ImagePhoto.image = UIImage(data: imageData)!
            }
        }


        let tapGesture = UITapGestureRecognizer(target: self, action: #selector(ReusableImageDisplayVC.tapFunction(sender:)))
        tapGesture.numberOfTapsRequired = 1
        ImagePhoto.addGestureRecognizer(tapGesture)
        view.addGestureRecognizer(tapGesture)

    }



    @objc func tapFunction(sender: UITapGestureRecognizer) {
        dismiss(animated: true, completion: nil)
    }


}

这里出了什么问题？

Answer 1

当你展示ReusableImageDisplayVC 视图控制器时，displayedImage 尚未设置。这是因为您在异步调用完成之前呈现视图控制器。试试这个：

@IBAction func openImageBarButtonDidPressed(_ sender: Any) {
    NetworkingService.fetchData(url: urlImage!) { [weak self] (result) in
        var displayedImage = UIImage()
        let imagePath = "https://example.com/someimage.jpg"
        let urlImage = URL(string: imagePath)

        self?.activityIndicator.startAnimating()

        switch result {
        case .failure(let error) :
            self?.activityIndicator.stopAnimating()
            self?.showAlert(alertTitle: "Sorry", alertMessage: error.localizedDescription, actionTitle: "Back")
            return //return instead of presenting ReusableImageDisplayVC 
        case .success (let imageData):
            self?.activityIndicator.stopAnimating()
            displayedImage = UIImage(data: imageData)!
        }

        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let popup = storyboard.instantiateViewController(withIdentifier: "imageDisplay") as! ReusableImageDisplayVC
        popup.photo = displayedImage

        self?.present(popup, animated: true, completion: nil)
    }
}

（注意在fetchData完成处理程序中使用[weak self]、self?和return）