检查Swift中的Firebase快照是否等于零 [英] Checking if Firebase snapshot is equal to nil in Swift

问题描述

我试图查询Firebase，以检查是否有任何用户拥有等待：1，然后当快照返回时，我想查看它是否等于零。我试图做到这一点，但我用的方法是行不通的，如果快照不等于零，我只有某种输出。我已经添加了我目前拥有的代码和Firebase的JSON文本。

 导入UIKit 
导入Firebase 
 import spring 
 
 class GamesViewController：UIViewController {
 
 let ref = Firebase（url：https://123test123.firebaseio.com）
 var activityIndi​​cator： UIActivityIndi​​catorView = UIActivityIndi​​catorView（）
 
 @IBAction func StartGamePressed（sender：AnyObject）{$ b $ print（test1）
 var peopleWaiting：[String] = [] 
 
 let userRef = Firebase（url：https://123test123.firebaseio.com/users）
 userRef.queryOrderedByChild（waiting）。queryEqualToValue（1）
 .observeEventType （.ChildAdded，withBlock：{在
中快照print（snapshot.key）
如果snapshot.key == nil {
 print（test2）
 let userData = [等待：1] 
 let usersRef = self.ref.childByAppendingPath（users）
 let hopperRef = u sersRef.childByAppendingPath（\（self.ref.authData.uid））
 
 hopperRef.updateChildValues（userData，withCompletionBlock：{
（error：NSError ?, ref：Firebase！）在
 if（error！= nil）{
 print（Data can not be saved。）
 self.displayAlert（Oops！，message：我们一直无法得到你进入一个游戏，检查你有一个互联网连接。如果这个问题继续支持）
} 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）
 
 
 
 }）
 
 $ b $ else {
 var randomUID：String 
 peopleWaiting.append（snapshot.key）
 let randomIndex = Int（arc4random_uniform（UInt32 peopleWaiting.count）））
 randomUID = peopleWaiting [randomIndex] $ b $ print（randomUID）
 let storyboard = UIStoryboard（name：Main，bundle：nil）
 let Home： UIViewController = storyboard.instantiateViewCont rollerWithIdentifier（continueToGame）
 self.presentViewController（Home，animated：true，completion：nil）
 $ b} 
}）
} 
 
 $ 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） - >无效在
 
））））
 
 self.presentViewController（formEmpty，animated：true，completion：nil）
} 
 
 func activityIndi​​catorFunction（）{
 
 activityIndi​​cator = UIActivityIndi​​catorView（frame：CGRectMake（0，0，100，100））
 activityIndi​​cator.backgroundColor = UIColor（red：0.16，green：0.17，blue：0.21 ，alpha：1）
 activityIndi​​cator.layer.cornerRadius = 6 
 activityIndi​​cator.center = self.view.center 
 activityIndi​​cator.hidesWhenStopped = true 
 activityIndi​​cator.activityIndi​​catorViewStyle = UIActivityIndi​​catorViewStyle.WhiteLarge 
 view.addSubview（activityIndi​​cator）
 activityIndi​​cator.startAnimating（）
 UIApplication.sharedApplication（）。beginIgnoringInteractionEvents（）
 
 
 
 
 
 
 
 
 JSON数据：
 
 <$ p 
 $ {
68e42b7f-aea5-4c3f-b655-51a99cb05bb0：{
email：[e-mail]，
username ：test1，
等待
，
，
8503d5a8-fc4a-492b-9883-ec3664898b4f：{
email：[e-mail]，
用户名：test2，
waiting：0
} 
} 
  

有一些事情在这里进行，但最重要的是你不能测试的孩子是否存在.ChildAdded

。如果你仔细想一想，这是有道理的：当一个孩子被添加到位置时，会引发 .ChildAdded 事件。如果没有添加子项，则不会引发该事件。



因此，如果要测试某个位置是否存在子项，则需要使用。价值。一旦你这样做，有各种方式来检测存在。这里有一个：

$ $ p $ $ $ $ $ $ ref.queryOrderedByChild（waiting）。queryEqualToValue（1）
.observeEventType（。值，withBlock {快照
print（snapshot.value）
if！snapshot.exists（）{
print（test2）
}
}） ;


I am trying to query Firebase to check if any user that has waiting: "1" and then when the snapshot is returned I want to see whether it is equal to nil. I have attempted to do this but the method I have used does not work and I only have some sort of out put if the snapshot is not equal to nil. I have added the code I currently have and the JSON text from Firebase.

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 Data:

{
"68e42b7f-aea5-4c3f-b655-51a99cb05bb0" : {
  "email" : "[e-mail]",
  "username" : "test1",
  "waiting" : "0"
},
"8503d5a8-fc4a-492b-9883-ec3664898b4f" : {
  "email" : "[e-mail]",
  "username" : "test2",
  "waiting" : "0"
}
}

解决方案

There are a few things going on here, but the most important one is that you cannot test for the existence of children with .ChildAdded. That makes sense if you think about it: the .ChildAdded event is raised when a child is added to the location. If no child is added, the event won't be raised.

So if you want to test if a child exists at a location, you need to use .Value. Once you do that, there are various way to detect existence. Here's one:

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

这篇关于检查Swift中的Firebase快照是否等于零的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！