关于firebase：void函数中意外的非void返回值 – Swift

Unexpected non-void return value in void function – Swift

不让我返回用户名值，因为它在闭包中。有人可以向我解释如何使用 @escaping 和 void 闭包

错误：void 函数中出现意外的非 void 返回值

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func grabUsername () -> String {
let uid = Auth.auth().currentUser?.uid
let database = Firestore.firestore().collection(“Users”).document(uid!)
database.getDocument { (docSnapshot, error) in
guard let docSnapshot = docSnapshot, docSnapshot.exists else {return}
let mydata = docSnapshot.data()
let username = mydata![“Username”] as? String ??””
return username
}
}

与其返回字符串值，不如将其设为闭包，因为 database.getDocument 在闭包中也会返回错误。

所以让你的函数成为一个闭包。

像这样。

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func grabUsername (completion: @escaping (Error?, String?) -> Void) {
let uid = Auth.auth().currentUser?.uid
let database = Firestore.firestore().collection(“Users”).document(uid!)
database.getDocument { (docSnapshot, error) in
if error != nil { completion(error.localizedDescription!, nil) } else { guard let docSnapshot = docSnapshot, docSnapshot.exists else {return}
let mydata = docSnapshot.data()
let username = mydata![“Username”] as? String ??””
completion(nil, username)
}
}
}

getDocument 是异步方法，回调闭包没有返回，所以你不能从它返回，相反你必须在某处应用结果，例如。在属性

所以解决方法可以如下

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var username: String =””

// … other your code

func grabUsername () { // << async, no immediate return
let uid = Auth.auth().currentUser?.uid
let database = Firestore.firestore().collection(“Users”).document(uid!)
database.getDocument { (docSnapshot, error) in
guard let docSnapshot = docSnapshot, docSnapshot.exists else {return}
let mydata = docSnapshot.data()
let username = mydata![“Username”] as? String ??””

DispatchQueue.main.async {
self.username = username // << store result
}
}
}

来源：https://www.codenong.com/61436167/

Unexpected non-void return value in void function – Swift

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