在 Swift 中检查 Firebase 快照是否等于 nil

Question

我正在尝试查询 Firebase 以检查是否有任何用户拥有 waiting: "1"，然后当返回快照时，我想查看它是否等于 nil。我试图这样做，但我使用的方法不起作用，如果快照不等于 nil，我只有某种输出。我已经添加了我目前拥有的代码和来自 Firebase 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 数据：

{
"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

这里发生了一些事情，但最重要的是您无法使用.ChildAdded 测试孩子的存在。如果您考虑一下，这是有道理的：将孩子添加到该位置时会引发 .ChildAdded 事件。如果没有添加孩子，则不会引发事件。

所以如果你想测试一个位置是否存在一个孩子，你需要使用.Value。一旦你这样做了，就有多种方法可以检测存在。这是一个：

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

Answer 2

检查 NSNull。这是观察节点的代码。查询的工作方式大致相同。

这是一个完整且经过测试的应用。要使用，请将字符串“existing”更改为您知道存在的某个路径，例如您的用户路径，并将“notexisting”更改为某个不存在的路径

    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")
        }

    })

请注意，使用 .Value 可以保证返回结果，并且该块将始终触发。如果您的代码使用了 .ChildAdded，那么该块只会在孩子存在时触发。

此外，请检查以确保您的数据在 Firebase 中的显示方式。

users
   user_0
     waiting: 1

如果不同

users
   user_0
     waiting: "1"

请注意，“1”与 1 不同。