在 Swift 中使用闭包从函数中检索字符串值 [英] Retrieve String value from function with closure in Swift

问题描述

我正在尝试从 Firebase 检索字符串值，以便获取每个用户名和传递给该函数的唯一 UID，该函数返回用户的用户名.但是 - 由于 firebase ObserveEvent 在 closures 中，我无法返回任何值，因为操作发生异步(?).我想知道这是否是一种实现方式?

I am trying to retrieve a string value from Firebase in order to get each username with an unique UID that is passed to the function, which returns the username of the user. However - since the firebase ObserveEvent is in closures, I can't return any value back because the actions happens asynchronous(?). I was wondering if it was a way of accomplishing this?

函数如下所示:

func GetUsername(uid:String) -> String {
    var username = String()
    firebase.child("Users").child(uid).observeSingleEventOfType(.Value) { (snapshot:FIRDataSnapshot) in

        username = snapshot.value!["Username"] as! String

    }

    return username
}

显然这不起作用，但我希望能够通过执行 GetUsername("whatevertheidmightbe") 来获取数据.想法?

Obviously this doesn't work, but I want to be able to get the data by doing a GetUsername("whatevertheidmightbe"). Ideas?

推荐答案

你需要像这样创建完成处理程序

You need to create completion handler like this

func GetUsername(uid:String , completion: (String) -> ()) {
    firebase.child("Users").child(uid).observeSingleEventOfType(.Value) { (snapshot:FIRDataSnapshot) in
    if let username = snapshot.value!["Username"] as? String
        completion(username)
    }
    else {
        completion("")
    }
}

然后这样调用函数

self.GetUsername(str) { (name) -> () in
    if name.characters.count > 0 {
         print(name)
    }
    else {
         print("Not found")
    }
}

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