Swift Firebase Query 由数据库中的每个更改启动

Question

我创建了一个从 Firebase 加载数据的应用程序。为了节省资源并使应用程序尽可能经济，我实现了查询来为客户端加载合适的数据。那是代码:

    ref.queryOrdered(byChild: "name").queryEqual(toValue: "test").observe(.value, with:{ (snapshot: DataSnapshot) in

        if snapshot.exists(){
            ref.queryOrdered(byChild: "hometown").queryEqual(toValue: "munich").observe(.value, with:{ (snapshot: DataSnapshot) in


                for users in snapshot.children.allObjects as! [DataSnapshot]{
                    if users.key as! String != userId{
                        let item = users.value as? [String: AnyObject]
                        let userid = users.key as! String
                        let Username  = item?["name"] as! String
                        let Userage = item?["age"] as! String
                        let ProfileImage = item?["profileImageUrl"] as! String
                        let firstImage = item?["firstimage"] as! String
                        let seccondImage = item?["seccondimage"] as! String
                        let thirdImage = item?["thirimage"] as! String
                        let fourthImage = item?["fourthimage"] as! String
                        let fifthImage = item?["fifthimage"] as! String
                        let sixtImage = item?["sixtimage"] as! String
                        let sex = item?["sex"] as! String
                        let gender = item?["gender"] as! String
                        let info = item?["info"] as! String
                        let userItem = UserObject(userId: userid, name: Username, age: Userage, sex: sex, gender: gender, profileImage: ProfileImage, fistImage: firstImage, seccondImage: seccondImage, thirdImage: thirdImage, fourthImage: fourthImage, fifthImage: fifthImage, info: info, sixtImage: sixtImage)
                          self.checkValidFences(userItem: userItem, gf: gf)

                    }
                }


            })
        }

    })

不幸的是，当数据库中发生某些变化时，该方法总是加载数据。这就是为什么我总是在更改数据库中的某些内容后得到冗余值的原因。有没有办法只解析一次值

Answer 1

您可以通过 Reading data once 解决这个问题

You can use the observeSingleEventOfType method to simplify this scenario: the event callback added triggers once and then does not trigger again.

---

observeSingleEvent(of:with:)

This is equivalent to observeEventType:withBlock:, except the block is immediately canceled after the initial data is returned.

更多信息在这里:

https://firebase.google.com/docs/reference/swift/firebasedatabase/api/reference/Classes/DatabaseReference#observesingleeventofwith