ios - 将数据库中的值读入数组

Question

我正在尝试从数据库中读取并将值放入一个字符串数组中。但是，当我尝试将值插入数组然后打印该数组时，应用程序崩溃了。

var pets: [String]?

override func viewDidLoad() {
    super.viewDidLoad()

    let userRef = FIRDatabase.database().reference().child("users").child((FIRAuth.auth()?.currentUser?.uid)!).child("pets")
    userRef.observeSingleEvent(of: .value, with: { snapshot in
        if let snap = snapshot.value as? Bool {
            print("no values")
        } else if let snap = snapshot.value as? NSDictionary {
            for value in snap {
                print(value.key as! String)    // Prints out data in the database
                self.pets?.append(value.key as! String)
            }
            print(self.pets!)

        }
    })

有谁知道为什么 print(value.key as!String) 打印出数据，但是当我打印出数组时，应用程序崩溃并显示 unexpectedly found nil while unwrapping an Optional值?

Answer 1

您永远不会初始化宠物。您将其声明为可选但从未为其分配值。为什么不将您的代码更改为以下内容:

var pets = [String]() // start with an empty array 

override func viewDidLoad() {
    super.viewDidLoad()

    let userRef = FIRDatabase.database().reference().child("users").child((FIRAuth.auth()?.currentUser?.uid)!).child("pets")
    userRef.observeSingleEvent(of: .value, with: { snapshot in
        if let snap = snapshot.value as? Bool {
            print("no values")
        } else if let snap = snapshot.value as? NSDictionary {
            for value in snap {
                print(value.key as! String)    // Prints out data in the database
                self.pets.append(value.key as! String)
            }
            print(self.pets)

        }
    })