为什么函数返回nil FireBase Swift

本文介绍了为什么函数返回nil FireBase Swift的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

为什么函数都返回nil ?！我尝试添加DispathQue，但我不知道它应该是正确的！请帮助

Why ever function return nil?! I try add DispathQue but I don't understand how it should be right! Pls Help

func storagePutData(uid: String, image: UIImage, compretition: @escaping (Error?) -> Void) -> String { var downloadURL: String! let imageName = NSUUID().uuidString let uploadDara = UIImageJPEGRepresentation(image, 0.1)! let ref = self.refStorage.child("usersProfileImage/\(uid)/\(imageName).png") ref.putData(uploadDara, metadata: nil) { (metaDara, error) in if let err = error { compretition(err) } ref.downloadURL(completion: { (url, error) in if let err = error { compretition(err) } else { downloadURL = url?.absoluteString } }) } return downloadURL }

推荐答案

在被调用者函数中的异步函数完成执行之前，您将返回 downloadURL .此时，它将具有 nil 值，这是正确的.您将希望使用完成处理程序在 downloadURL 准备就绪时返回它，例如-

You're returning downloadURL before the asynchronous function within your callee function has finished execution. At this point, it will have nil value, which is correct. You'll want to use a completion handler to return downloadURL when its ready, like -

func storagePutData(uid: String, image: UIImage, success:@escaping (String?)->(), error: @escaping (Error?) -> Void) { var downloadURL: String! let imageName = NSUUID().uuidString let uploadDara = UIImageJPEGRepresentation(image, 0.1)! let ref = self.refStorage.child("usersProfileImage/\(uid)/\(imageName).png") ref.putData(uploadDara, metadata: nil) { (metaDara, error) in if let err = error { error(err) } ref.downloadURL(completion: { (url, error) in if let err = error { error(err) } else { downloadURL = url?.absoluteString success(downloadURL) } }) } }