本文介绍了检查Swift中的Firebase快照是否等于零的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我试图查询Firebase，以检查是否有任何用户拥有
我试图查询Firebase，以检查是否有任何用户拥有
。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" : "[email protected]",
"username" : "test1",
"waiting" : "0"
},
"8503d5a8-fc4a-492b-9883-ec3664898b4f" : {
"email" : "[email protected]",
"username" : "test2",
"waiting" : "0"
}
}
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")
}
});
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