Ios 在将图像保存到文档目录后更新bool变量不会’；在Swift中无法按预期工作

我正在使用我的应用程序的用户配置文件页面。我有一个全局bool变量（updateProfile），默认设置为false。当用户对其配置文件信息进行任何更改（如更改/删除其配置文件图片）时，数据库将更新，图像将下载并保存在documents目录中。以下是下载后保存图像的代码：

struct Downloads {

    // Create a static variable to start the download after tapping on the done button in the editUserProfile page
    static var updateProfile: Bool = false

    static func downloadUserProfilePic() {

        Database.database().reference().child("Users").child(userID!).child("Profile Picture URL").observeSingleEvent(of: .value) { (snapshot) in
        guard let profilePictureString = snapshot.value as? String else { return }
        guard let profilePicURL = URL(string: profilePictureString) else { return }

        let session = URLSession(configuration: .default)

        let downloadPicTask = session.dataTask(with: profilePicURL) {
                (data, response, error) in

            if let e = error {
                print("error downloading with error: \(e)")

            } else {
                if let res = response as? HTTPURLResponse {
                    Downloads.imageCached = true // The image has been downloaded
                    print("Downloaded with \(res.statusCode)")

                    if let imageData = data {
                        let image = UIImage(data: imageData)

                        // Now save the image in the documents directory
                        // Get the url of the documents directory
                        let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
                        // Name your image with the user ID to make it unique
                        let imageName = userID! + "profilePic.jpg"
                        // Create the destination file URL to save the image
                        let imageURL = documentsDirectory.appendingPathComponent(imageName)
                        print(imageURL)
                        let data = image?.jpegData(compressionQuality: 0.5)

                        do {
                            // Save the downloaded image to the documents directory

                            // Write the image data to disk
                            try data!.write(to: imageURL)
                            print("Image Saved")
                            updateProfile = true

                        } catch {
                            print("Error saving file \(error)")
                        }


                    } else {
                        print("Couldnt get image")
                    }

                } else {
                    print("Couldnt't get response")
                }
            }
        }
        downloadPicTask.resume()        

    }
}

SomeOtherViewController

// When the user taps on the 'done' button
@objc func doneButtonTapped() {

    uploadUserSelectedPicture()

}

func uploadUserSelectedPicture() {

    // Download the profile picture and save it
    Downloads.downloadUserProfilePic()

    if Downloads.updateProfile == true {
        // Go to the user profile page
        let userProfilePage = UserProfilePage()
        self.present(userProfilePage, animated: true)
    }

}

如您所见，一旦图像保存到documents目录，并且updateProfile全局变量更改为true，我就会打印“Image saved”。在另一个ViewController上，仅当updateProfile变量为true（这意味着图像应保存到documents目录）时，才会显示页面（当点击done按钮时）

---

但唯一的问题是，在保存图像之前，变量被设置为true，我如何知道这一点？我知道这一点，因为页面是在执行print语句

print（“图像保存”）

之前显示的。为什么会发生这种情况？有什么办法可以解决这个问题吗？

实际上，您的代码应该永远不会显示页面。但是，由于在调用

downloadUserProfilePic

之前忘记将

updateProfile

显式设置为

false

，因此显示的页面中没有第二次调用的图像

然而，

observe

和

dataTask

都是异步工作的。您必须添加一个完成处理程序

简单形式：

---

---

我得到这个错误：-[UIView init]只能从主线程使用

static var updateProfile: Bool = false  

static func downloadUserProfilePic(completion: @escaping () -> Void) {

...

    do {
       // Save the downloaded image to the documents directory

       // Write the image data to disk
       try data!.write(to: imageURL)
       print("Image Saved")          
       completion()
    }

...

func uploadUserSelectedPicture() {

    // Download the profile picture and save it
    Downloads.downloadUserProfilePic { [weak self] in
        // Go to the user profile page
        DispatchQueue.main.async {
           let userProfilePage = UserProfilePage()
           self?.present(userProfilePage, animated: true)
        }
    }

}