从Firebase打印数据

问题描述：

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，控制台将打印出Firebase中的数据.启动应用程序后，当我按它时，控制台将打印一个空数组.当我再次按下它时，控制台会打印出我想要的结果.我想让它在第一次尝试中打印出正确的结果.我该怎么办?

The idea here is that when I press the submit button, console will print out data from Firebase. After launching the app, when I press it, the console print an empty array. when I press it again, the console printed the result I wanted. I want to make it print the correct result on the 1st try. How do I do this ?

答

您正在打印数据源，在您的情况下，它是Firebase调用完成之前的self.array.您需要做的是:

You are printing your datasource, in your case, it's the self.array before your Firebase call completes. What you need to do is either:

在完成块内打印数据，如下所示:

Print your data inside the completion block, like so:

@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)

    }
}

或者，如果您真的想在submitAnswer函数中打印数据，那么您将需要在getData()函数中添加一个完成块，就像这样.

Or if you really want to print your data inside your submitAnswer function, then you would need a completion block in your getData() function, like so.

@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)

        }
    }

让我知道这是否有帮助.

Let me know if this helps.

从Firebase打印数据

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