ios - 如何从 firebase 存储 Swift 4 ios 检索图像

Question

我正在尝试从 firebase 存储中检索图像，但出于某种原因，我检索到的图像始终为 nil。

var ref: DatabaseReference!
var storageRef: StorageReference!
var hallData = [Hall]()
override func viewDidLoad() {
    let refHandle = Database.database().reference().child("hallData").observe(DataEventType.value, with: { (snapshot) in
        let postDict = snapshot.value as? [String : AnyObject] ?? [:]
         let values = Array(postDict.values)
        //print(values)
        let valueDict = values as! [[String:Any]]

        for i in valueDict
        {
            var name = i["name"] as! String
            var address = i["address"] as! String
            var capacity = i["capacity"] as! String
            var decorations = i["decorations"] as! String
            var highPrice = i["highPrice"] as! String
            var lowPrice = i["lowPrice"] as! String
            var catering = i["catering"] as! String
            var email = i["email"] as! String
            self.storageRef = Storage.storage().reference().child("images").child(email)
            var image: UIImage!
            // Download in memory with a maximum allowed size of 1MB (1 * 1024 * 1024 bytes)

            self.storageRef.getData(maxSize: 1 * 1024 * 1024) { data, error in

                if let error = error {
                    print("PLASESEE")
                    print(error.localizedDescription)
                    // Uh-oh, an error occurred!
                } else {
                    // Data for "images/island.jpg" is returned
                    let image = UIImage(data: data!)
                }
            }
        print(image)
            self.hallData.append(Hall(name2: name, capacity2: capacity, lowPrice2: lowPrice, highPrice2: highPrice, catering2: catering,decorations2: decorations, address2:address, image2: image, email2: email))
        }
    })
}

我不明白我做错了什么，我遵循了 firebase 存储上的 api，检查了很多教程，但我一直得到 nil

Answer 1

问题是您正试图在 getData 闭包之外使用image var。

    self.storageRef.getData(maxSize: 1 * 1024 * 1024) { data, error in
            if let error = error {
                print("PLASESEE")
                print(error.localizedDescription)
                // Uh-oh, an error occurred!
            } else {
                // Data for "images/island.jpg" is returned
                let image = UIImage(data: data!)
            } <- closure ends here and image is only valid above this
        }
        print(image) <- image may not be populated at this point
        self.hallData.append... image
    }

该闭包是异步的，对 self.hallData.append... 的调用将在闭包中填充图像变量之前发生。代码比互联网快得多

将该语句移到闭包中，紧跟在 let image = 之后，它应该可以工作。

       self.storageRef.getData(maxSize: 1 * 1024 * 1024) { data, error in
           if let error = error {
               print("An error occurred in downloading the image")
               print(error.localizedDescription)
           } else {
               let image = UIImage(data: data!)
               self.hallData.append... image
               //reload your tableView or UI as self.hallData is now valid
           }
       }

如果您这样做，前面的 var image: UIImage! 可以删除，因为它没有任何功能。否则，删除闭包内 let image = 之前的 le​​t。