檢查Swift中的Firebase快照是否等於零

Question

我試圖查詢Firebase以檢查是否有waiting: "1"的用戶，然後當快照返回時，我想查看它是否等於零。我試圖做到這一點，但我使用的方法不起作用，如果快照不等於零，我只有某種輸出。我添加了我目前擁有的代碼和Firebase中的JSON文本。

import UIKit 
import Firebase 
import Spring 

class GamesViewController: UIViewController { 

let ref = Firebase(url: "https://123test123.firebaseio.com") 
var activityIndicator: UIActivityIndicatorView = UIActivityIndicatorView() 

@IBAction func StartGamePressed(sender: AnyObject) { 
    print("test1") 
    var peopleWaiting: [String] = [] 

    let userRef = Firebase(url:"https://123test123.firebaseio.com/users") 
    userRef.queryOrderedByChild("waiting").queryEqualToValue("1") 
     .observeEventType(.ChildAdded, withBlock: { snapshot in 
      print(snapshot.key) 
      if snapshot.key == nil { 
       print("test2") 
       let userData = ["waiting": "1"] 
       let usersRef = self.ref.childByAppendingPath("users") 
       let hopperRef = usersRef.childByAppendingPath("\(self.ref.authData.uid)") 

       hopperRef.updateChildValues(userData, withCompletionBlock: { 
        (error:NSError?, ref:Firebase!) in 
        if (error != nil) { 
         print("Data could not be saved.") 
         self.displayAlert("Oops!", message: "We have been unable to get you into a game, check you have an internet conection. If this problem carries on contect support") 
        } else { 
         print("Data saved successfully!") 
         let storyboard = UIStoryboard(name: "Main", bundle: nil) 
         let Home : UIViewController = storyboard.instantiateViewControllerWithIdentifier("continueToGame") 
         self.presentViewController(Home, animated: true, completion: nil) 

        } 

       }) 


      } else { 
       var randomUID: String 
       peopleWaiting.append(snapshot.key) 
       let randomIndex = Int(arc4random_uniform(UInt32(peopleWaiting.count))) 
       randomUID = peopleWaiting[randomIndex] 
       print(randomUID) 
       let storyboard = UIStoryboard(name: "Main", bundle: nil) 
       let Home : UIViewController = storyboard.instantiateViewControllerWithIdentifier("continueToGame") 
       self.presentViewController(Home, animated: true, completion: nil) 

      } 
     }) 
} 

func displayAlert(title: String, message: String){ 

    let formEmpty = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.Alert) 
    formEmpty.addAction((UIAlertAction(title: "Ok", style: .Default, handler: { (action) -> Void in 

    }))) 

    self.presentViewController(formEmpty, animated: true, completion: nil) 
} 

func activityIndicatorFunction(){ 

    activityIndicator = UIActivityIndicatorView(frame: CGRectMake(0, 0, 100, 100)) 
    activityIndicator.backgroundColor = UIColor(red:0.16, green:0.17, blue:0.21, alpha:1) 
    activityIndicator.layer.cornerRadius = 6 
    activityIndicator.center = self.view.center 
    activityIndicator.hidesWhenStopped = true 
    activityIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.WhiteLarge 
    view.addSubview(activityIndicator) 
    activityIndicator.startAnimating() 
    UIApplication.sharedApplication().beginIgnoringInteractionEvents() 

} 


} 

JSON數據：

{ 
"68e42b7f-aea5-4c3f-b655-51a99cb05bb0" : { 
    "email" : "test1@test1.com", 
    "username" : "test1", 
    "waiting" : "0" 
}, 
"8503d5a8-fc4a-492b-9883-ec3664898b4f" : { 
    "email" : "test2@test2.com", 
    "username" : "test2", 
    "waiting" : "0" 
} 
} 

Answer 1

有幾件事情怎麼回事，但最重要的一個就是你不能測試.ChildAdded的兒童是否存在。如果你仔細考慮，這是有道理的：當孩子被添加到位置時，會引發.ChildAdded事件。如果沒有添加小孩，則不會提高活動。

因此，如果您想測試某個位置是否存在小孩，則需要使用.Value。一旦你這樣做，有各種方式來檢測存在。這裏有一個：下面

ref.queryOrderedByChild("waiting").queryEqualToValue("1") 
    .observeEventType(.Value, withBlock: { snapshot in 
     print(snapshot.value) 
     if !snapshot.exists() { 
      print("test2") 
     } 
    }); 

Answer 2

檢查NSNull。這是觀察節點的代碼。查詢以同樣的方式工作。

這是一個完整的，經過測試的應用程序。要使用，修改字符串「現有的」一些你知道的路徑存在，比如您的用戶路徑和「notexisting」一些路徑不存在

let myRootRef = Firebase(url:"https://your-app.firebaseio.com") 
    let existingRef = myRootRef.childByAppendingPath("existing") 
    let notExistingRef = myRootRef.childByAppendingPath("notexisting") 

    existingRef.observeEventType(.Value, withBlock: { snapshot in 

     if snapshot.value is NSNull { 
      print("This path was null!") 
     } else { 
      print("This path exists") 
     } 

    }) 

    notExistingRef.observeEventType(.Value, withBlock: { snapshot in 

     if snapshot.value is NSNull { 
      print("This path was null!") 
     } else { 
      print("This path exists") 
     } 

    }) 

請注意，通過使用.value的，會有保證返回結果，並且塊將始終開啓。如果你的代碼使用.ChildAdded，那麼該塊只會在小孩存在時觸發。

此外，請檢查以確保您的數據在Firebase中的顯示方式。

users 
    user_0 
    waiting: 1 

如果不同於

users 
    user_0 
    waiting: "1" 

注意，「1」是不一樣的1