当Firebase功能在Swift中结束时 [英] When Firebase function ends in Swift

问题描述

我在我的应用程序中使用Firebase，它查询大量用户并获取所需的特定数据，但是当它开始查询时-该功能的其余部分也保持运行，而不仅仅是查询，因此我可以不知道什么时候结束.

I am using a Firebase in my app, it queries through a lot of users and gets the specific data that is needed, but when it starts querying - the rest of the function keep running too, instead of just querying so I can't understand when it ends.

例如下面的代码:

ref.observeEventType(.ChildAdded, withBlock: { snapshot in

            let user = snapshot.value!.objectForKey("User")
            let name = (user!["Name"])! as! String

            print("name")

            })
print("done")

假设我们在Firebase数据库中有3个用户-打印的代码将是:

Let's say we have 3 users in the Firebase Database - the printed code will be:

done
nameuser1
nameuser2
nameuser3

(或done将在名称用户之间，取决于您的Internet连接-但不会是最后一个)

(or the done will be somewhere between the nameusers, depends on your internet connection - BUT it won't be the the last)

推荐答案

您遇到的问题"是由于函数observeEventType()是异步的.因此，它会在实际获取值之前将控制权返回给其调用方.使用这样的异步回调并传递一个函数，该函数每次在从firebase中检索值时都会被调用...

The "problem" your experiencing is due to the function observeEventType() being asynchronous. So it returns control to its caller before the values have actually been retrieved. Use an asynchronous callback like this and pass a function that will be called each time a value is retrieved from firebase...

已为Swift 3更新

func getDataFromFirebase(callback: @escaping (_ user: String, _ name: String)->Void){
   ref.observeEvent(of: .childAdded, with:{(snapshot)-> Void in

        let user = snapshot.value!.objectForKey("User") as! String
        let name = (user!["Name"])! as! String

        callback(user, name)

   })
}

并像这样调用函数...

and call the function like this...

getDataFromFirebase(callback: {(user, name)-> Void in 
    print("got a user: \(user) and a name: \(name)")
})

这将为检索到的每个孩子打印一个用户和一个名字

This will print a user and a name for every child that is retrieved

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