IOS Swift - 从Firebase数据库中的不同节点获取值

Question

我想要获取事件参与者列表，在事件节点中，只列出员工的ID号。我想实现的是从员工节点获取与该ID＃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 

，这里是我的代码

@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"] 
["", "", "", ""] 

全码：

@IBAction FUNC downloadButtonAction（_发件人：UIButton的）{

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的getName（forUID用户名：字符串，回调：@escaping（字符串） - >无效）{

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) 
     } 
    } 
}) 

}

不退还员工姓名。请帮忙。谢谢！

Answer 1

问题是，由于从火力此取是一个异步调用，所以你必须使用回调以获取名称到您所呼叫的GetName方法的功能，你可以做这样的事情：

@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) 

       } 
      } 
     }) 


    }