我试图在 firebase 数据库中写入一些数据,但是我得到了错误的运行过程。有人可以帮我吗?非常感谢!!
JSON树结构如下:
{
"cars": {
"auto id": [
"parts": "wheel"
...
.
.
.
@objc func buttonTapped(){
print("before running")
var ref = Database.database().reference(withPath: "cars").queryOrdered(byChild: "parts").queryEqual(toValue: "wheel")
ref.observeSingleEvent(of: .childAdded, with: { (snapshot) in
autoId = snapshot.key
print("running")
}) { (error) in
print(error.localizedDescription)
}
print("after running")
let newPlanetRef = Database.database().reference().child("company").childByAutoId()
newPlanetRef.updateChildValues(autoId)
}
我期望运行的进程是
"before running"->"running"->"after running"
但实际过程是
"before running"->"after running"->"running" And the data cannot be updated to database unless I put the update function inside the closure
最佳答案
这是一个异步过程。
你应该这样使用:
var newPlanetRef: String? //It should be your reference type
var ref = Database.database().reference(withPath: "cars").queryOrdered(byChild: "parts").queryEqual(toValue: "wheel")
ref.observeSingleEvent(of: .childAdded, with: { (snapshot) in
autoId = snapshot.key
newPlanetRef = Database.database().reference().child("company").childByAutoId()
newPlanetRef.updateChildValues(autoId)
print("running")
}) { (error) in
print(error.localizedDescription)
}
但我认为这样使用:
为您的引用 key 创建私有(private)枚举:
private enum ReferenceKeys { static let carsKey = "cars" }
创建数据库引用的全局变量:
var database = Database.database() var databaseReference = database.reference() var carReference = database.reference(withPath: ReferencesKeys.carsKey)
像这样使用您的函数:
var newPlanetRef: String? var reference = carReference.queryOrdered(byChild: "parts").queryEqual(toValue: "wheel") reference.observeSingleEvent(of: .childAdded, with: { [weak self] snapshot in self?.autoId = snapshot.key newPlanetRef = databaseReference.child("company").childByAutoId() newPlanetRef.updateChildValues(autoId) print("running") }) { error in print(error.localizedDescription) }
奖励:
您可以使用 dispatchGroup(或信号量)等待快照值以进行:
调度组
@objc func buttonTapped(){
let dispatchGroup = DispatchGroup()
print("before running")
var ref = Database.database().reference(withPath: "cars").queryOrdered(byChild: "parts").queryEqual(toValue: "wheel")
dispatchGroup.enter()
ref.observeSingleEvent(of: .childAdded, with: { [weak self]snapshot in
self?.autoId = snapshot.key
dispatchGroup.leave()
print("running")
}) { (error) in
print(error.localizedDescription)
}
print("after running")
let newPlanetRef = Database.database().reference().child("company").childByAutoId()
newPlanetRef.updateChildValues(autoId)
}
调度信号量
@objc func buttonTapped(){
let dispatchSemaphore = DispatchSemaphore(value: 1)
print("before running")
var ref = Database.database().reference(withPath: "cars").queryOrdered(byChild: "parts").queryEqual(toValue: "wheel")
ref.observeSingleEvent(of: .childAdded, with: { [weak self]snapshot in
self?.autoId = snapshot.key
semaphore.signal()
print("running")
}) { (error) in
print(error.localizedDescription)
}
semaphore.wait()
print("after running")
let newPlanetRef = Database.database().reference().child("company").childByAutoId()
newPlanetRef.updateChildValues(autoId)
}
完成
@objc func buttonTapped(){
getData { [weak self] snapshotKey in
self?.autoId = snapshot.key
let newPlanetRef = Database.database().reference().child("company").childByAutoId()
newPlanetRef.updateChildValues(self?.autoId)
}
}
/// completion type -(String?)- must be a snapshot.key's type
func getData(_ completion: @escaping (String?) -> Void) {
print("before running")
var ref = Database.database().reference(withPath: "cars").queryOrdered(byChild: "parts").queryEqual(toValue: "wheel")
ref.observeSingleEvent(of: .childAdded, with: { snapshot in
completion?(snapshot.key)
print("running")
}) { (error) in
print(error.localizedDescription)
}
print("after running")
}
关于swift - 从 firebase 数据库查询数据时的奇怪行为,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/56898986/