为什么我的Firebase存储URL没有上传到Google Cloud Firestore？

Question

func uploadProfilePic() -> String {
     guard let imageData = profilePic?.jpegData(compressionQuality: 0.75) else {
         print("Unable to get image data.")
         return ""
     }

     let imageID = UUID().uuidString
     let profilePhotosRef = Storage.storage().reference().child("profilePhotos/\(imageID).jpg")

     let uploadMetadata = StorageMetadata()
     uploadMetadata.contentType = "image/jpeg"

     var downloadURL = String()
     profilePhotosRef.putData(imageData, metadata: uploadMetadata) { (downloadMetadata, err) in
         if let err = err {
             self.showAlertWithOK(title: "An Error Occurred", message: "There was an error uploading your profile photo. Try again later in Hostend settings.")
             print("An error occurred: \(err.localizedDescription)")
         }

         profilePhotosRef.downloadURL { (url, err) in
             if let url = url {
                 downloadURL = url.absoluteString
             }
         }
     }

     return downloadURL
}

db.collection("users").document(uid).setData(["profile_pic_url": uploadProfilePic(), "name": name, "phone_number": phoneNumber, "fcm_token": token, "timestamp": Date()])

我希望图像的下载URL在“profile_pic_url”下上传到Firestore，但这没有发生。相反，它只是一个空的字符串即使该映像已成功地存储到Firebase中。

Answer 1

不能对包含闭包的函数使用return语句，因为函数将在闭包执行之前返回。

而是将函数更改为使用完成处理程序，如

func uploadProfilePic(completion: @escaping (String?, Error?) -> ()) {

然后，一旦获得下载url，就调用处理程序。

    profilePhotosRef.downloadURL { (url, err) in
      completion(url, err)
    }

   self.uploadProfilePic() { (url, error) in

    guard error....

    if let url = url {
      // do your upload here
    }
}