Firebase / Firestore没有获取文档和运行代码

Question

我在swift中从firebase获得文档。但是，该行没有运行，也没有获取数据。

这是我的代码:

let db = Firestore.firestore()
db.collection("chats").document(userDefaults.string(forKey: "currentGroup")!).collection("messages").document("variable").getDocument { (document, error) in
if error != nil{
print("error getting document")
}
else{
let documentData = document!.data()
let startNumOfMessages = documentData!["numOfMessages"] as! Int
var messageArray: Array<String> = []
if startNumOfMessages > 0 {
for message in 1...startNumOfMessages{
print(message)
//THIS LINE ISNT RUNNING
db.collection("chats").document(self.userDefaults.string(forKey: "currentGroup")!).collection("messages").document("(message)").getDocument { (messageDoc, err) in
if err != nil{
print("Error getting message (message)")
}
else{
if messageDoc!.exists && messageDoc != nil{
let messData = messageDoc!.data()
print(messData!["message"]!)
messageArray.append(messData!["message"] as! String)
}
else{
print("error in document")
}
}
}
}
//Display them
for num in 0...messageArray.count{
let label = UILabel()
label.text = messageArray[num]
self.stackView.addArrangedSubview(label)
}
}
}
}

注释下面的行是没有运行的行。label.text = messageArray[num]这一行显示错误

致命错误:索引超出范围

显示它没有获取数据

Answer 1

您错过了异步方式使用DispatchGroup(编号从1到4)

let db = Firestore.firestore()
db.collection("chats").document(userDefaults.string(forKey: "currentGroup")!).collection("messages").document("variable").getDocument { (document, error) in
if error != nil{
print("error getting document")
}
else{
let documentData = document!.data()
let startNumOfMessages = documentData!["numOfMessages"] as! Int
var messageArray: Array<String> = []
if startNumOfMessages > 0 {
let g = DispatchGroup() /// 1
for message in 1...startNumOfMessages{
print(message)
//THIS LINE ISNT RUNNING
g.enter() /// 2
db.collection("chats").document(self.userDefaults.string(forKey: "currentGroup")!).collection("messages").document("(message)").getDocument { (messageDoc, err) in
if err != nil{
print("Error getting message (message)")
}
else{
if messageDoc!.exists && messageDoc != nil{
let messData = messageDoc!.data()
print(messData!["message"]!)
messageArray.append(messData!["message"] as! String) 
}
else{
print("error in document")
}
}
g.leave() /// 3
}
}
g.notify(queue: .main) {  /// 4
//Display them
for num in 0...messageArray.count{
let label = UILabel()
label.text = messageArray[num]
self.stackView.addArrangedSubview(label)
}
}
}
}
}