Question

我需要从该函数返回一个值，并且我有2个参数。我无法完成转义功能。如何使其逃脱？

func myReturn(str:String,userCU:String)->String{
        var res = ""
        let refU = Database.database().reference(withPath: "users")
        refU.child(userCU).observeSingleEvent(of:.value) {
                (snapshot) in

               if snapshot.exists(){
                   // print(snapshot)
                    let dict = snapshot.value as! [String:Any]
                    print(dict)
                    //dict["userCity"]
                    res = dict[str] as! String
                    print(res)


                }
                else {
                    print("noooooo")
            }
        }
       print(res)

         return res
    }

Answer 1

作为起点，我考虑在数据库调用失败的情况下返回可选的String。

func getStringAsync(str: String, usr: String, completion: @escaping (String?) -> Void) {

    Database.database().reference(withPath: "users").child(usr).observeSingleEvent(of: .value) { (snapshot) in

        if let snapshot = snapshot,
            let d = snapshot.value as? [String: Any],
            let result = d[str] as? String {
            completion(result)
        } else {
            completion(nil)
        }

    }

}

然后处理可选的String：

getStringAsync(str: "abc", usr: "xyz") { (str) in

    if let str = str {
        print(str)
    }

}

我需要从该函数返回一个值，我有2个参数。我无法完成转义功能

1 个答案: