swift - 如何从快照闭包返回数组的值并使用它来准备segue？

Question

我试图在函数外部获取数组的值。但是一旦快照 block 结束，newArray 的值就会变空。 即使在闭包结束后我也想访问数组的值。 将准备转场的值传递到下一个 View Controller 后，该值仍然为空。

var newArray = [Any]()
func getData(refe: String) -> [Any]{

    let currUser = Auth.auth().currentUser?.uid
    let ref = Database.database().reference(fromURL: "MyURL").child("users/\(currUser!)/Questions/")
    ref.child("\(refe)").observeSingleEvent(of: .childAdded, with:{ snapshot in

        let enumerator = snapshot.children
        while let rest = enumerator.nextObject() as? DataSnapshot, let value = rest.value{
            self.newArray.append(value as! Any)
        }
        print(self.newArray)
//This gives [test,test1,test2]

    })
    return newArray
// Here the Array is empty.
}

实际结果:[]

预期结果:[测试、测试1、测试2]

我也尝试过这个。

    func getData(refe: String, completion: @escaping (([Any]) -> ())) {
    var newArray = [Any]()
        let currUser = Auth.auth().currentUser?.uid
        let ref = Database.database().reference(fromURL: "MYURL").child("users/\(currUser!)/Questions/")
        ref.child("\(refe)").observeSingleEvent(of: .childAdded, with: { snapshot in

            let enumerator = snapshot.children
            while let rest = enumerator.nextObject() as? DataSnapshot, let value = rest.value{

                newArray.append(value)
            }

        completion(newArray)
    })
    }

并在辅助函数中调用它

func getDataD() -> [Any]{
    let ref = getReference()
    var arr = [Any]()
    self.getData(refe: ref) { (array) in
        arr = array
// This gives [test,test1,test2]
    }
    return arr
// This gives []
}

之后调用准备segue的函数

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

    guard let detailViewController = segue.destination as? HostOptionTableViewController
        else {
            return
    }
    detailViewController.ref = getReference()
    self.getData(refe: detailViewController.ref) { (array) in
        detailViewController.data = array
    }   
}   
}

detailViewController.data执行后的实际结果应该是[test,test1,test2] 但这是[]

Answer 1

在 prepareForSegue 中调用 getData 已经太晚了，这应该位于导航到第二个 vc 的操作内

 self.getData(refe:yourRef) { array in   
     self.performSegue(withIdentifier:"segueName",sender:array)
 }   


override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

    guard let detailViewController = segue.destination as? HostOptionTableViewController
        else {
            return
    }
    detailViewController.ref = getReference() 
    detailViewController.data = sender as! [Model] // Model is type of array     
}

请求是异步的，导航将在获取数据之前发生