将观察值转换为swift中的.childAdded [英] Convert observe .value to .childAdded in swift

问题描述

目前，我正在将这些代码从firebase数据库加载到数组中。由于这是在viewDidLoad里面，我必须清空我的数组食品= [] 之前加载数据到它，如果我不这样它就会复制所有的对象，我将有双重复第二次加载，第三次三倍等...但是，这不是一个很好的解决多种原因，所以我想是它只会添加新的对象从数据库与 .childAdded 然而，如果我只是用 .childAdded 切换 .value ，它会崩溃，我得到一个线程1：信号SIGABRT 在这一行： let dict = user_snap.value as！ [String：String？] 。我很新，迅速，不知道如何解决这个问题，真的很感谢一些帮助。
$ b $ pre $ let parentRef =数据库.database（）。reference（）。child（Recipes）
let storage = Storage.storage（）

parentRef.observe（.value，with：{snapshot in

if（snapshot.value is NSNull）{

// DATA未找到
print（ - - - Data was found - - - ）

} else {

//清除数组，使其不会加载重复数据
food = []

//数据发现$ b （snapshot.children）{

让user_snap = user_child as！DataSnapshot
let dict = user_snap.value as！[String：String？]

//定义标签变量
let recipeName = dict [Name] as？String
let recipeDescription = dict [Description] as？String
让downloadURL = dict [Image]为？字符串

let storageRef = storage.reference（forURL：downloadURL！）

storageRef.getData（maxSize：1 * 1024 * 1024）{（data，error） - >无效

let recipeImage = UIImage（data：data！）
$ b food.append（元素（名称：recipeName !,描述：recipeDescription !,图像：recipeImage！））
self.tableView.reloadData（）
}
}
}
}）


解决方案

 让dict = user_snap.value as！ [字符串：字符串？] 
  

而不是

 让dict = snapshot.value as！ Dictionary< String，String> 
  

也许你可以做空测试：

 让dict = snapshot.value as！ Dictionary< String，String> 
 
如果让recipeName = dict [Name]作为字符串!,让recipeDescription = dict [Description] as String !,让downloadURL = dict [Image] as String！ 
 {
 let storageRef = storage.reference（forURL：downloadURL）
 $ b $ storageRef.getData（maxSize：1 * 1024 * 1024）{（data，error） - >无效
 
 let recipeImage = UIImage（data：data！）
 
 food.append（元素（名称：recipeName，描述：recipeDescription，图像：recipeImage !, downloadURL：downloadURL ））
 self.tableView.reloadData（）
} 
} 
 else 
 {
 print（Error！Could not decode data）
} 
  

Currently I'm having some problems with this bit of code that is loading data from firebase database into an array. Since this is inside of viewDidLoad I have to empty my array food = [] before loading the data into it, if I don't then it will duplicate all the objects and I will have double duplicates the second time it loads, triple the third time and etc... However this was not a good fix for multiple reasons so what I would like is that it would only add new objects from the database with .childAdded however if I just switch out .value with .childAdded it will crash, I get a Thread 1: signal SIGABRT on this line: let dict = user_snap.value as! [String: String?]. I am pretty new to swift and don't know how to fix this, would really appreciate some help.

let parentRef = Database.database().reference().child("Recipes")
let storage = Storage.storage()

parentRef.observe(.value, with: { snapshot in

        if ( snapshot.value is NSNull ) {

            // DATA WAS NOT FOUND
            print("– – – Data was not found – – –")

        } else {

            //Clears array so that it does not load duplicates
            food = []

            // DATA WAS FOUND
            for user_child in (snapshot.children) {

                let user_snap = user_child as! DataSnapshot
                let dict = user_snap.value as! [String: String?]

                //Defines variables for labels
                let recipeName = dict["Name"] as? String
                let recipeDescription = dict["Description"] as? String
                let downloadURL = dict["Image"] as? String

                let storageRef = storage.reference(forURL: downloadURL!)

                storageRef.getData(maxSize: 1 * 1024 * 1024) { (data, error) -> Void in

                    let recipeImage = UIImage(data: data!)

                    food.append(Element(name: recipeName!, description: recipeDescription!, image: recipeImage!))
                    self.tableView.reloadData()
                }
            }
        }
    })

解决方案

let dict = user_snap.value as! [String: String?]

Instead of

let dict = snapshot.value as! Dictionary<String, String>

and maybe you can do null test :

let dict = snapshot.value as! Dictionary<String, String>

if let recipeName = dict["Name"] as String!, let recipeDescription = dict["Description"] as String!, let downloadURL = dict["Image"] as String!
{
    let storageRef = storage.reference(forURL: downloadURL)

    storageRef.getData(maxSize: 1 * 1024 * 1024) { (data, error) -> Void in

        let recipeImage = UIImage(data: data!)

        food.append(Element(name: recipeName, description: recipeDescription, image: recipeImage!, downloadURL: downloadURL))
        self.tableView.reloadData()                        
    }                    
}
else
{
    print("Error! Could not decode data")                    
}

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