无法从 firebase 获得价值

Question

当我尝试从我的数据库中获取 isBusy 属性的值时遇到问题。一个使用过的断点，它甚至没有转到我为 isBusy 分配值的指令，它分配空字符串并转到 else 条件。

if docChild == 0 {
        let selectedDoctor = Doctors.doc1
        var isBusy = String()

        databaseHandle = reference.child(selectedDoctor).child(dateChild).child(timeChild).child(ReservationFields.isBusy).observe(.childAdded, with: { (snapshot) in
            isBusy = snapshot.value as! String
        })

        if isBusy == "false" {
            reference.child(selectedDoctor).child(dateChild).child(timeChild).child(ReservationFields.isBusy).setValue("true")
            reference.child(selectedDoctor).child(dateChild).child(timeChild).child(ReservationFields.firstname).setValue(firstNameLabel.text)
            reference.child(selectedDoctor).child(dateChild).child(timeChild).child(ReservationFields.lastname).setValue(lastNameLabel.text)
            reference.child(selectedDoctor).child(dateChild).child(timeChild).child(ReservationFields.pesel).setValue(peselLabel.text)
            reference.child(selectedDoctor).child(dateChild).child(timeChild).child(ReservationFields.telephone).setValue(phoneLabel.text)


        } else {
            createAlert(title: "Przepraszamy - termin jest zajęty", message: "Proszę wybrać inny termin")

        }

database

Answer 1

答案很简单。 Firebase 数据库请求是异步的，因此在您到达 if isBusy == "false" 语句时，该值并未从数据库中获取。相应地更改您的代码：

if docChild == 0 {
    let selectedDoctor = Doctors.doc1
    var isBusy = String()

    databaseHandle = reference.child(selectedDoctor).child(dateChild).child(timeChild).child(ReservationFields.isBusy).observe(.childAdded, with: { (snapshot) in
        isBusy = snapshot.value as! String
        if isBusy == "false" {
            reference.child(selectedDoctor).child(dateChild).child(timeChild).child(ReservationFields.isBusy).setValue("true")
            reference.child(selectedDoctor).child(dateChild).child(timeChild).child(ReservationFields.firstname).setValue(firstNameLabel.text)
            reference.child(selectedDoctor).child(dateChild).child(timeChild).child(ReservationFields.lastname).setValue(lastNameLabel.text)
            reference.child(selectedDoctor).child(dateChild).child(timeChild).child(ReservationFields.pesel).setValue(peselLabel.text)
            reference.child(selectedDoctor).child(dateChild).child(timeChild).child(ReservationFields.telephone).setValue(phoneLabel.text)


        } else {
            createAlert(title: "Przepraszamy - termin jest zajęty", message: "Proszę wybrać inny termin")

        }
   })

如您所见，我只是将您的代码移入处理程序，因此它会在获取您的值后执行。