IOS Swift - 从Firebase数据库中的不同节点获取值

Question

我想获取一个事件的参与者列表，在事件节点中，只列出了该员工的id＃。我想要实现的是从 Employee 节点获取与该id相关联的名称。这是我的dbase的结构。

events:
     uuid:
        name: summer festival 2017
        site: vegas
        participants:
           employeeID1: true
           employeeID2: true 

Employee:
    employeeID1:
       name: gary
       department: video production

这是我的代码

@IBAction func downloadButtonAction(_ sender: UIButton) {

      ref.child("events").child(eventKeyLabel.text!).child("participants").observeSingleEvent(of: .value, with: {(snapshot) in

            // get the dictionary from the snapshot
            if let participantsDict = snapshot.value as? [String : AnyObject] {


                for each in participantsDict {

                    let employeeIDNum = each.key
                    let employeeName = self.getName(forUID: employeeIDNum)

                    self.employeeID.append(employeeIDNum)
                    self.name.append(employeeName)

                }

              print(self.employeeID)
              print(self.name)

            }

        }) // End observeSingleEvent

    }


    func getName(forUID userID: String) -> String{

        var empName = ""

        ref.child("Employee").child(userID).observe(DataEventType.value, with: { (snapshot) in
            if let value = snapshot.value as? NSDictionary {

                empName = (value["name"] as? String)!
            }
        })

       return empName
    }

结果：

["0001", "0002", "0003", "0004"]
["", "", "", ""]

完整代码：

@IBAction func downloadButtonAction（_ sender：UIButton）{

ref.child("events").child(eventKeyLabel.text!).child("participants").observeSingleEvent(of: .value, with: {(snapshot) in

    // get the dictionary from the snapshot
    if let participantsDict = snapshot.value as? [String : AnyObject] {


        for each in participantsDict {

            let employeeIDNum = each.key
            self.getName(forUID: employeeIDNum) { empName in
                self.name.append(empName)
                print(empName)
            }

            self.employeeID.append(employeeIDNum)


        }

        print(self.employeeID)
        print(self.name)

    }

}) // End observeSingleEvent

}

func getName（forUID userID：String，callback：@escaping（String） - ＆gt; Void）{

ref.child("Employee").child(userID).observe(DataEventType.value, with: { (snapshot) in
    if let value = snapshot.value as? NSDictionary {
        print(value)
        if let empName = value["name"] as? String{
            callback(empName)
        }
    }
})

}

它不会返回员工姓名。请帮忙。谢谢！

Answer 1

问题是，因为从firebase获取是异步调用，所以你必须使用回调来获取调用getName方法的函数的名称，你可以这样做：

@IBAction func downloadButtonAction(_ sender: UIButton) {

      ref.child("events").child(eventKeyLabel.text!).child("participants").observeSingleEvent(of: .value, with: {(snapshot) in

            // get the dictionary from the snapshot
            if let participantsDict = snapshot.value as? [String : AnyObject] {


                for each in participantsDict {

                    let employeeIDNum = each.key
                    self.getName(forUID: employeeIDNum)

                    self.employeeID.append(employeeIDNum)


                }

              print(self.employeeID)
              print(self.name)

            }

        }) // End observeSingleEvent

    }


    func getName(forUID userID: String) {



        ref.child("Employee").child(userID).observe(DataEventType.value, with: { (snapshot) in
            if let value = snapshot.value as? NSDictionary {
                print(value) //add here
                if let empName = value["name"] as? String{
                       self.name.append(empName)

                }
            }
        })


    }