在 Swift 中等待异步操作完成 [英] Wait For Asynchronous Operation To Complete in Swift

问题描述

我不知道如何处理这种情况，因为我对 iOS 开发和 Swift 非常陌生.我正在执行这样的数据获取:

I am not sure how to handle this situation as I am very new to iOS development and Swift. I am performing data fetching like so:

func application(application: UIApplication!, performFetchWithCompletionHandler completionHandler: ((UIBackgroundFetchResult) -> Void)!)
{
    loadShows()
    completionHandler(UIBackgroundFetchResult.NewData)
    println("Background Fetch Complete")
}

我的 loadShows() 函数解析从加载到 UIWebView 的网站获取的一堆数据.问题是我有一个在 loadShows 函数中等待 10 秒左右的计时器.这允许页面中的 javascript 在我开始解析数据之前完全加载.我的问题是完成处理程序在我的 loadShows() 之前完成.

My loadShows() function parses a bunch of data it gets from a website loaded into a UIWebView. The problem is that I have a timer that waits for 10 seconds or so in the loadShows function. This allows for the javascript in the page to fully load before I start parsing the data. My problem is that the completion handler completes before my loadShows() does.

我想要做的是为isCompletedParsingShows"添加一个 bool 并让 completionHandler 行等待完成，直到该 bool 为真.处理此问题的最佳方法是什么?

What I would like to do is add a bool for "isCompletedParsingShows" and make the completionHandler line wait to complete until that bool is true. What is the best way to handle this?

推荐答案

您必须将异步函数传递给处理程序以便稍后调用:

you have to pass your async function the handler to call later on:

func application(application: UIApplication!, performFetchWithCompletionHandler completionHandler: ((UIBackgroundFetchResult) -> Void)!) {
    loadShows(completionHandler)
}

func loadShows(completionHandler: ((UIBackgroundFetchResult) -> Void)!) {
    //....
    //DO IT
    //....

    completionHandler(UIBackgroundFetchResult.NewData)
    println("Background Fetch Complete")
}

或(恕我直言，更清洁的方式)

添加一个中间的completionHandler

OR (cleaner way IMHO)

add an intermediate completionHandler

func application(application: UIApplication!, performFetchWithCompletionHandler completionHandler: ((UIBackgroundFetchResult) -> Void)!) {
    loadShows() {
        completionHandler(UIBackgroundFetchResult.NewData)
        println("Background Fetch Complete")
    }
}

func loadShows(completionHandler: (() -> Void)!) {
    //....
    //DO IT
    //....
    completionHandler()
}

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