訪問一個函數外的變量 - swift

Question

我想喲訪問一個函數外的變量，我試圖聲明變量之外的類，但它始終顯示聲明中的初始值不是函數內的值，在這裏是我的代碼，我需要訪問databaseScore

func getDatabaseScore()-> Int{ 
    let ref2 = FIRDatabase.database().reference().child("users").child("user").child((user?.uid)!) 

    ref2.observeSingleEvent(of: .childAdded, with: { (snapshot) in 
     if var userDict = snapshot.value as? [String:Int] { 
      //Do not cast print it directly may be score is Int not string 
      var databaseScore = userDict["score"] 

     } 


    }) 

    return databaseScore 

} 

Answer 1

正如評論這是不可能返回的東西形成含有異步任務的方法提及。

你需要一個完成的塊例如

func getDatabaseScore(completion: (Int?)->()) { 
    let ref2 = FIRDatabase.database().reference().child("users").child("user").child((user?.uid)!) 

    ref2.observeSingleEvent(of: .childAdded, with: { (snapshot) in 
     if let userDict = snapshot.value as? [String:Int] { 
      //Do not cast print it directly may be score is Int not string 
      completion(userDict["score"]) 
     } 
     completion(nil) 
    }) 
} 

---

getDatabaseScore() { score in 
    guard let score = score else { return } 
    // do something with unwrapped "score" 
} 

Answer 2

你做一個異步操作，之前getDatabaseScore回報observeSingleEvent完成。你可以看看這樣的事情...

class MyClass { 

    var databaseScore: Int = 0 

    func getDatabaseScore() { 

     let ref2 = FIRDatabase.database().reference().child("users").child("user").child((user?.uid)!) 

     ref2.observeSingleEvent(of: .childAdded, with: { (snapshot) in     
      if let userDict = snapshot.value as? [String:Int] { 
       print(userDict["score"]) // Confirm you have the a value 
       self.databaseScore = userDict["score"] 
      } 
     } 
    }