Swift 4与Firebase数据库或Firestore读/写

Question

我对iOS开发相当陌生，对数据库集成也很陌生。简而言之，我正在尝试创建一个水跟踪器。在实时数据库和Firestore中，我都可以写入新数据和更新数据。当我关闭并重新打开应用程序时，控制台会打印当前存储的值。我正在努力将这种价值观融入一个标签中。我的字典是setup(例如)["Cups of Water："x]，我想把x的值放在标签中，但我似乎无法提取这个值。

我似乎无法克服的另一个问题是附加数据库存储的内容，而不是完全覆盖。当我关闭/重新打开应用程序时，控制台会打印"15"(例如)，排除了我将值导入标签的问题，如果我触摸添加杯按钮，它将覆盖"15"的值，现在显示"1"。

这显然是我没有正确添加的内容，我对问题所在有一些想法，但我不太清楚。非常感谢任何意见！

下面的代码是特定于Firestore的。我可以在实时数据库中使用类似的过程(通过使用正确的语法)。代码：

@IBOutlet weak var totalWaterLabel: UILabel!
var ref: DocumentReference? = nil
var variableCupsOfWater = 0
var handle: AuthStateDidChangeListenerHandle?
var waterListener: FIRListenerRegistration!
override func viewDidLoad() {
super.viewDidLoad()
}
@IBAction func addOnePressed(_ sender: UIButton) {
variableCupsOfWater += 1
totalWaterLabel.text = String(variableCupsOfWater)
saveToFirestore()
}
@IBAction func addTwoPressed(_ sender: Any) {
variableCupsOfWater += 2
totalWaterLabel.text = String(variableCupsOfWater)
saveToFirestore()
}
@IBAction func addFourPressed(_ sender: UIButton) {
variableCupsOfWater += 4
totalWaterLabel.text = String(variableCupsOfWater)
saveToFirestore()
}
func saveToFirestore() {
let _: DocumentReference? = nil
let db = Firestore.firestore()
let user = Auth.auth().currentUser
let uid = user!.uid
db.collection("By User").document("(uid)").updateData([
"Cups Of Water": "(totalWaterLabel.text!)",
"Date": NSDate()
]) { err in
if let err = err {
print("Error adding document: (err)")
} else {
print("Document added")
}
}
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
handle = Auth.auth().addStateDidChangeListener({ (auth, user) in
print(Auth.auth().currentUser as Any)
})
let db = Firestore.firestore()
let user = Auth.auth().currentUser
let uid = user!.uid

db.collection("By User").document("(uid)")
.addSnapshotListener { querySnapshot, error in
guard let querySnapshot = querySnapshot, querySnapshot.exists else {return}
let myData = querySnapshot.data()
let currentWaterTotal = myData["Cups of Water:"] as? String ?? ""
let combinedCups = ("(currentWaterTotal)") + self.totalWaterLabel.text!
self.totalWaterLabel.text = "(querySnapshot.data())"
if let error = error {
print("Error retreiving collection: (error)")
}else{
print("Current data: (String(describing: querySnapshot.data()))")
}
}

Answer 1

首先，你必须精确匹配密钥，所以我认为你应该试试这个：

myData["Cups Of Water"] 

而不是

myData["Cups of Water:"]

使用此选项可以安全地从可选的中打开值

if let cupsOfWater = myData["Cups Of Water"] as? String { 
self.totalWaterLabel.text = cupsOfWater 
}

这被称为optional binding语法，您可以在这里了解更多

https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/TheBasics.html