全局变量似乎失去了价值（swift）

Question

这是我从firebase中提取数据的代码。
listofnames（二维）和名称（单维）是String类型的全局数组。

但是，当我打印listofnames时，输出窗口中会显示一个空数组，而如果我在注释第一行（self.listofnames = [[]]）时代码正常工作。

我已将链接引用与Firebase数据库

请帮忙。

var databasehandle:FIRDatabaseHandle? 

let time = ["8AM - 9AM", "9AM - 10AM","10AM - 11AM", "11AM -12PM", "12PM - 1PM","1PM - 1:30PM","2PM - 3PM","3PM - 4PM","4PM - 5PM","5PM - 6PM","6PM - 7PM","7PM - 7:30PM"] 

var ref:FIRDatabaseReference! 
var day: String = "Monday" 
var users :String = "First years" 

func loaddata() 
{ 
    self.listofnames = [[]] 
    for x in 0...((time.count)-1) 
    { 
     ref.child(users).child(day).child(time[x]).observeSingleEvent(of: .value, with: {(snapshot) -> Void in 
      if let namesfromFirebase = snapshot.value as? [String:Any] 
      { 
       let y = namesfromFirebase.count 
       for i in 1...y 
       { 
        self.names.append(namesfromFirebase["s"+"\(i)"] as! String) 
       } 
      } 
      self.listofnames.append(self.names) 
      self.names = [] 
     }) 
    } 
    print(self.listofnames) 
    self.tableView.reloadData() 
} 

Answer 1

observeSingleEvent异步工作，闭包稍后调用。

有一个简单的解决方案：移动两行到封闭：

func loaddata() 
{ 
    self.listofnames = [[]] 
    for x in 0..<time.count // no parentheses and math needed when using `..<` 
    { 
     ref.child(users).child(day).child(time[x]).observeSingleEvent(of: .value, with: {(snapshot) -> Void in 
       if let namesfromFirebase = snapshot.value as? [String:Any] 
       { 
        let y = namesfromFirebase.count 
        for i in 1...y 
        { 
         self.names.append(namesfromFirebase["s"+"\(i)"] as! String) 
        } 
       } 
       self.listofnames.append(self.names) 
       self.names = [] 
       print(self.listofnames) 
       self.tableView.reloadData() 
     }) 
    } 
}