从Firebase检索数据不起作用

Question

我有以下代码，以便检索餐馆及其数据列表。但是，它不存储数据，每次我尝试返回数组时它返回nil。但如果我打印它，打印数据。有什么建议吗？

func getRestaurants()-> Array<Restaurant>{
    var baruri = [Restaurant]()
    dataBaseRef.child("AthensRestaurants/Restaurants").observe(.value, with: { (snapshot) in

        if let snapshot = snapshot.children.allObjects as? [FIRDataSnapshot] {
            for snap in snapshot {
                print(snap)
                if let restaurantData = snap.value as? Dictionary<String, AnyObject> {
                    let restaurant = Restaurant(restaurantData: restaurantData)
                    baruri.append(restaurant)
                    print(baruri)


                }
            }
        }
    })
    return baruri
}

Answer 1

firebase observe是一个异步回调函数，因此它将在完成后运行。换句话说，您的return baruri将始终在值返回之前运行。您可以使用完成处理程序来获取所需的值。

var restaurants = [Restaurant]()

func getRestaurants(completion: @escaping (Array<Restaurant>) -> Void){
    var baruri = [Restaurant]()
    dataBaseRef.child("AthensRestaurants/Restaurants").observe(.value, with: { (snapshot) in

        if let snapshot = snapshot.children.allObjects as? [FIRDataSnapshot] {
            for snap in snapshot {
                print(snap)
                if let restaurantData = snap.value as? Dictionary<String, AnyObject> {
                    let restaurant = Restaurant(restaurantData: restaurantData)
                    baruri.append(restaurant)
                    print(baruri)

                    completion(baruri)
                }
            }
        }
    })
}

// Call this function with call back 
getRestaurants { restaurants in
    self.restaurants = restaurants
}