ios - 从 Firebase 打印数据

Question

这是我的代码:

@IBAction func submitAnswer(_ sender: Any) {
    getData()
    print(array)
}

func getData() {
    let ref = Database.database().reference().child("hobbies")
    let query = ref.queryOrdered(byChild: "cost").queryEqual(toValue: "low" )
    query.observe(.childAdded, with: { snapshot in
        let hobbyName = snapshot.childSnapshot(forPath: "hobbyName").value as? String
        self.array.append(hobbyName!)
    })
    { error in
        print(error)
    }
}

这里的想法是，当我按下提交按钮时，控制台将从 Firebase 打印出数据。启动应用程序后，当我按下它时，控制台会打印一个空数组。当我再次按下它时，控制台打印出我想要的结果。我想让它在第一次尝试时打印出正确的结果。我该怎么做？

Answer 1

您正在打印数据源，在您的例子中，它是 Firebase 调用完成之前的 self.array。您需要做的是:

1. 在完成 block 中打印数据，如下所示:

   @IBAction func submitAnswer(_ sender: Any) {
       getData()
   }
   
   func getData() {
       let ref = Database.database().reference().child("hobbies")
       let query = ref.queryOrdered(byChild: "cost").queryEqual(toValue: "low" )
       query.observe(.childAdded, with: {( snapshot) in
           self.array.append((snapshot.childSnapshot(forPath: "hobbyName").value as? String)!)
           print(array) // Print inside this block instead :)
       }) { (error) in
           print(error)
   
       }
   }
   

2. 或者，如果您确实想在 submitAnswer 函数中打印数据，那么您需要在 getData() 函数中添加一个完成 block ，如下所示.

   @IBAction func submitAnswer(_ sender: Any) {
           getData {
               // Completed! Now you can print your updated data from your datasource.
               print(array)
           }
       }
   
   func getData(withBlock completion: @escaping () -> Void) {
           let ref = Database.database().reference().child("hobbies")
           let query = ref.queryOrdered(byChild: "cost").queryEqual(toValue: "low" )
           query.observe(.childAdded, with: {( snapshot) in
               self.array.append((snapshot.childSnapshot(forPath: "hobbyName").value as? String)!)
               completion()
           }) { (error) in
               print(error)
   
           }
       }
   

请告诉我这是否有帮助。