Firebase返回结果后为变量赋值？

Question

我已经为此苦苦挣扎了 2 个小时。我正在使用 Firebase 数据库和存储在 Swift 中构建一个应用程序。

目标是更新用户资料。用户有 2 张图片 - 个人资料和标题。现在，我必须首先检查他们是否从照片库中选择了一张图片，如果没有 - 只需从数据库中获取旧 URL 并将其与其余更新信息一起提交回数据库。如果是新选择的图像，请将图像上传到存储，使用 downloadURL 取回 URL，将其分配给 var storageHeaderDownloadedURL 和/或 var storageProfileDownloadedURL，并将字符串值与其余用户数据一起提交到 Firebase 数据库.

问题在于，在我取回下载的 URL 之前，它显然分配了一个空的 String 的值（我已经声明了它们）。如果用户不更新图像但 UITextFields 的其余部分都可以正常工作，则旧 URL 将提交到 Firebase 数据库。

我的问题是如何从存储中执行下载的 URL 方法，然后将其分配给 var storageHeaderDownloadedURL 和 var storageProfileDownloadedURL 第一手？

func updateUserProfile ()
{
    if let userID = FIRAuth.auth()?.currentUser?.uid
    {
        // Note: Storage references to profile images & profile headers folder
        let storageUserProfileID = Storage.storage.profile_images.child(userID)
        let storageUserHeaderID = Storage.storage.profile_headers.child(userID)

        guard let imageProfile = profileImage.image else { return }

        guard let headerImage = headerImage.image else { return }


        if let newProfileImage = UIImagePNGRepresentation(imageProfile), let newHeaderImage = UIImagePNGRepresentation(headerImage)
            {
                storageUserProfileID.put(newProfileImage, metadata: nil, completion: { (metadata, error) in

                    if error != nil
                    {
                        showAlert(title: "Oops!", msg: (error?.localizedDescription)!, actionButton: "OK", viewController: self)
                        return
                    }
                    // Get the URL from the storage
                    storageUserProfileID.downloadURL(completion: { (url, error) in

                        if error != nil
                        {
                            showAlert(title: "Oops!!!", msg: (error?.localizedDescription)!, actionButton: "OK", viewController: nil)
                            return
                        }
                        else
                        {
                            if let profileImgDownloadedURL = url?.absoluteString
                            {
                                self.storageProfileDownloadedURL = profileImgDownloadedURL
                                print(self.storageProfileDownloadedURL)
                                self.selectedProfileImage = .True
                            }
                        }

                    })
                })
                storageUserHeaderID.put(newHeaderImage, metadata: nil, completion: { (metadata, error) in

                    if error != nil
                    {
                        showAlert(title: "Oops!", msg: (error?.localizedDescription)!, actionButton: "OK", viewController: self)
                        return
                    }

                    // Get the URL from the storage
                    storageUserHeaderID.downloadURL(completion: { (url, error) in

                        if error != nil
                        {
                            showAlert(title: "Oops!!!", msg: (error?.localizedDescription)!, actionButton: "OK", viewController: self)
                            return
                        }
                        else
                        {
                            if let headerImgDownloadedURL = url?.absoluteString
                            {
                                self.storageHeaderDownloadedURL = headerImgDownloadedURL
                                print(self.storageHeaderDownloadedURL)
                                self.selectedHeaderImage = .True
                            }
                        }
                    })
                })


        //Note: Update the info for that user in Database


        print(self.storageHeaderDownloadedURL)
        print(self.storageProfileDownloadedURL)


        var finalHeaderImageURL = String()

        switch self.selectedHeaderImage {

        case .True:
            finalHeaderImageURL = self.storageHeaderDownloadedURL
            break

        case .False:
            finalHeaderImageURL = self.oldHeaderImageInDB
            break

        }
        print(finalHeaderImageURL)


        var finalProfileImageURL = String()

        switch self.selectedProfileImage {

        case .True:
            finalProfileImageURL = self.storageProfileDownloadedURL
            break

        case .False:
            finalProfileImageURL = self.oldProfilePhotoImageInDB
            break

        }
        print(finalProfileImageURL)

        guard let newDisplayName = self.displayNameTextField.text else { return }
        guard let newLocation = self.locationTextField.text else { return }
        guard let newDescription = self.bioTextField.text else { return }
        guard let newWebsite = self.websiteTextField.text else { return }
        guard let newBirthday = self.birthdayTextField.text else { return }

        let newUpdatedUserDictionary = ["imageProfile": finalProfileImageURL,
                                        "imageHeader" : finalHeaderImageURL,
                                        "description" : newDescription,
                                        "location": newLocation,
                                        "displayName": newDisplayName,
                                        "website": newWebsite,
                                        "birthday": newBirthday,
                                        ]
        Database.dataService.updateUserProfile(uid: userID, user: newUpdatedUserDictionary)

        showAlert(title: "Hey", msg: "Your profile was updated", actionButton: "OK", viewController: self)
         } // Get new uploaded profile and header image URLs
    }
}

我用于 switch 语句的枚举来确定它是旧 URL 还是新 URL：

 enum SelectedHeaderImage
 {
  case True
  case False
 }

 enum SelectedProfileImage
 {
 case True
 case False
 }

班级网点：

var storageProfileDownloadedURL = String()
var storageHeaderDownloadedURL = String()  

var oldProfilePhotoImageInDB = String()
var oldHeaderImageInDB = String()

var selectedHeaderImage = SelectedHeaderImage.False
var selectedProfileImage = SelectedProfileImage.False`

Answer 1

据我了解，您的问题在于排队。您希望下面的代码在下载完成后执行，但它以正常流程执行。如果这是您的问题，那么我建议您创建另一个enum，具有三个下载状态/计数。并将该代码移到您希望稍后在函数中执行的下方。下载完成后增加新enum 的状态。它看起来像这样：

enum DownloadCount
{
    case Zero
    case One
    case Two
}
var downloadCount = DownloadCount.Zero

并且在您下载完成的每个成功块中将其更改为，我将在这里写一个，让您了解需要做什么。

if let profileImgDownloadedURL = url?.absoluteString
{
     self.storageProfileDownloadedURL = profileImgDownloadedURL
     print(self.storageProfileDownloadedURL)
     self.selectedProfileImage = .True
     if(downloadCount == .Zero)
     {
         downloadCount = DownloadCount.One
     }
     else
     {
         downloadCount = DownloadCount.Two
     }
     self.newAssigningFunction()
}

func newAssigningFunction()
{
    if(downloadCount == .Two)
    {
        //Do your storage/saving work here
    }
}

此外，如果您需要再次执行此功能，最好在您的updateUserProfile 功能开始时将downloadCount 设置回Zero。如果不清楚或者您需要进一步的帮助，请告诉我。或者，如果这不是您的情况。