等待在Swift中完成异步操作 [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，因为我是iOS开发和Swift的新手。我正在执行数据提取：

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中的网站获得的一堆数据。问题是我有一个在loadShows函数中等待10秒左右的计时器。这允许在我开始解析数据之前完全加载页面中的javascript。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.

我想做的是为isCompletedParsingShows添加一个bool，并使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

您必须将您的异步函数传递给稍后调用的处理程序：

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（清洁方式恕我直言）

添加中间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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