Swift 3的异步功能和Firebase [英] Asynchronous functions and Firebase with Swift 3

问题描述

我读了一些有关此的问题.但是我仍然对异步功能有疑问.

I read some questions about that. But I still have issues with asynchronous functions.

例如:我有一个 viewController1 ，其中一个按钮对 viewController2 执行了搜索.在 viewController2 类中，我在另一个名为 exampleClass 的类文件中初始化一些值.这些值是从Firebase数据库或位置值中检索的.这些值需要一点时间来检索.我将这些值从 exampleClass 返回到我的 viewController2 中.我在 viewController2 viewDidLoad()中打印这些值.

For example: I have a viewController1 where a button perform a segue to a viewController2. In the viewController2 class, I initialize some values in another class file named exampleClass. These values are retrieved from Firebase database or location values. These values need a little moment to be retrieved. I return thes values from the exampleClass into my viewController2. I print these values in the viewController2 viewDidLoad().

我的问题:设备不等待取回值并执行以下功能.结果:当我触摸按钮时，打印的值是 nil 值.如果我不保护代码，它也会使应用程序崩溃.

My issue: The device doesn't wait that the values are retrieved and execute following functions. Result: When I touch the button, printed values are nil values. It can also make the app crash if I don't secure the code.

到目前为止，我发现的信息:我了解到，我只需要在Firebase snapshot (例如)的末尾调用一个func，如下所示:

What I've found so far: I learned that I only have to call a func at the end of a Firebase snapshot (for example) like this:

    userRef.observeSingleEvent(of: .value, with: { (snapshot) -> Void in
        self.name = snapshot.value as! String!
        print(self.name)
        self.forceEnd()
    }) { (error) in
        print(error.localizedDescription)
    }

我将此函数命名为 forceEnd 以使其清晰.这对我不起作用.我也尝试创建处理程序，但没有任何积极结果.

I named this function forceEnd to be clear. This is not working for me. I also tried to create handlers but no positive results.

我的问题:在执行以下问题之前，如何强制设备等待检索值?

My question: How can I force the device to wait for the values to be retrieved before performing the following question?

推荐答案

在执行以下问题之前，如何强制设备等待取回值?

How can I force the device to wait for the values to be retrieved before performing the following question?

• 您不想强制等待设备，只需要在从Firebase数据库中检索到这些值后执行一些操作即可.
• 可以以多种方式异步执行操作，例如协议，通知等
• You don't want to force the device to wait, only need to perform some operations once these values are retrieved from Firebase database.
• Performing an operation asynchronously can be done in multiple ways like blocks, protocols, notifications, etc.

通常，积木是更优雅的方法.
一些示例代码可能类似于:


Generally, blocks are the more elegant approach.
Some sample code can be like:


func myFirebaseNetworkDataRequest(finished: () -> Void) { // the function thats going to take a little moment

     ...

     print("Doing something!") // firebase network request

     finished()    
}


// usage of above function can be as-

override func viewDidLoad() {

     myFirebaseNetworkDataRequest {

          // perform further operations here after data is fetched
          print("Finally! It took a lot of moments to end but now I can do something else.")
     }
}

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