Swift 在完成块之外使用变量

Im当前正在从firebase检索数据。数据被放入一个

NSObject

中，然后放入一个完成块。完成块内的项存储为变量

userBinfos

。变量

userBinfos

仅在完成块内部工作我想在完成块外部使用它

var userBinfos = userObject()
    override func viewDidLoad() {
        super.viewDidLoad()

        userBinfo { (user) in
        self.userBinfos = user

        }  
//I want to use to variable here but it does not work 
        print(self.userBinfos.email)

    }


    func userBinfo(completion: (userObject) -> ()) {

        let dbFir = FIRDatabase.database().reference()

        let firRef = dbFir.child("frontEnd/users/\(userId)")

        firRef.observeEventType(.Value, withBlock: { snapshot in

            let userDict = snapshot.value as! [String: AnyObject]
            self.name.text = userDict["firstname"] as? String
            self.userBio.text = userDict["userBio"] as! String

            var user = userObject()

            user.firstName = userDict["firstname"]
            user.lastName = userDict["lastname"]
            user.email = userDict["email"]
            user.profileImageUrl = userDict["profileImageUrl"]
            user.userBio = userDict["firstname"]
            user.userId = userDict["firstname"]

                   dispatch_async(dispatch_get_main_queue(), {
            completion(user)

            })

        }) { (error) in
            print(error)
        }

    }

---

userBinfo

的

completion

参数的全部目的是提供一种机制，用于在调用异步

observeEventType

时获得通知。因此，在

userBinfo{user in…}

闭包中，根据异步方法的完成情况编写代码

如果UI的一部分在调用异步的

完成

闭包之前没有意义，那么让

viewDidLoad

配置UI使其显式（可能显示

UIActivityIndicatorView

或其他内容），然后在完成处理程序中删除该内容

override func viewDidLoad() {
    super.viewDidLoad()

    // do whatever you want to let the user know that something asynchronous
    // is happening, e.g. add a spinning `UIActivityIndicatorView` or whatever

    userBinfo { user in
        self.userBinfos = user

        // Update the UI here, including removing anything we presented to let
        // the user know that the asynchronous process was underway. If you were
        // dealing with UITableView`, you'd call `tableView.reloadData()` here.
    }  

    // but not here
}

---

您正在区块外调用print（self.userBinfos.email）！！将它放在内部：userBinfo{（user）in}，因此在块

observeEventType

分配之前调用它，这意味着在

viewDidLoad

完成之后调用完成块。将要在完成块之外执行的代码放入块中，就完成了。