从一个从firebase中检索数据的闭包获取数据 [英] getting data out of a closure that retrieves data from firebase

问题描述

我正在尝试从Firebase检索数据，并将数据存储在检索数据的闭包外部。

I am trying to retrieve data from Firebase and store that data outside of the closure that retrieves that data.

    var stringNames = [String] ()
    ref?.observeEventType(.Value, withBlock: { snapshot in
        var newNames: [String] = []
        for item in snapshot.children {
            if let item = item as? FIRDataSnapshot {
                let postDict = item.value as! [String: String]
                newNames.append(postDict["name"]!)
            }
        }
        stringNames = newNames
    })
    print(stringNames)

stringNames回来为空，但是当我从闭包中打印时，它有正确的数据。任何帮助将非常感谢，谢谢！

stringNames comes back empty, but when I print from inside the closure it has the correct data. Any help would be much appreciated, thank you!

推荐答案

这是因为当你从Firebase获取数据调用是异步。你可以做什么：

That's because when you fetch data from Firebase the call is Asynchronous. What you can do:

选项1 - 在闭包内设置你的逻辑（就像你在闭包内打印var一样）。

Option 1 - Set your logic inside the closure (Like what you have that print the var inside the closure).

选项2 - 定义自己的闭包，它将接收您的数据：

Option 2 - Define your own closure that going to receive your data like:

func myMethod(success:([String])->Void){

    ref?.observeEventType(.Value, withBlock: { snapshot in
        var newNames: [String] = []
        for item in snapshot.children {
            if let item = item as? FIRDataSnapshot {
                let postDict = item.value as! [String: String]
                newNames.append(postDict["name"]!)
            }
        }
        success(newNames)
    })
}

选项3 - 使用委托模式

Option 3 - Use the delegate pattern

protocol MyDelegate{
     func didFetchData(data:[String])
}

class MyController : UIViewController, MyDelegate{

    func myMethod(success:([String])->Void){
        ref?.observeEventType(.Value, withBlock: { snapshot in
           var newNames: [String] = []
           for item in snapshot.children {
               if let item = item as? FIRDataSnapshot {
                   let postDict = item.value as! [String: String]
                   newNames.append(postDict["name"]!)
               }
            }
            self.didFetchData(newNames)
        })
    }

    func didFetchData(data:[String]){
        //Do what you want
    }

}

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