swift - 如何在用户需要时终止功能？

Question

我有一个从网络获取数据的函数。但是，虽然执行此功能，但需要一段时间。因此我添加了一个停止按钮。但是如何在用户点击停止按钮时终止功能？

终止函数:

func getData(param: String) -> String{

        //param can be one of these = row, name, channel, rating, share
        var xPath: String = ""
        if param == "row" {
            xPath = "/html/body/table[4]/tr[4]/td[@class='sayfa_ic']/table/tr[2]/td/table//tr/td[1]/b"
        } else if param == "name" {
            xPath = "/html/body/table[4]/tr[4]/td[@class='sayfa_ic']/table/tr[2]/td/table//tr/td[2]"
        } else if param == "channel" {
            xPath = "/html/body/table[4]/tr[4]/td[@class='sayfa_ic']/table/tr[2]/td/table//tr/td[3]"
        } else if param == "rating" {
            xPath = "/html/body/table[4]/tr[4]/td[@class='sayfa_ic']/table/tr[2]/td/table//tr/td[4]"
        } else if param == "share" {
            xPath = "/html/body/table[4]/tr[4]/td[@class='sayfa_ic']/table/tr[2]/td/table//tr/td[6]"
        } else {
            return ""
        }
        let html = Ji(htmlURL: NSURL(string: URL!)!)//takes a while
        let titleNode = html!.xPath(xPath)!
        return String(titleNode)
    }

Answer 1

如果您正在使用 NSURLSessionTask，请调用 task.cancel()。

文档:

/* -cancel returns immediately, but marks a task as being canceled.
 * The task will signal -URLSession:task:didCompleteWithError: with an
 * error value of { NSURLErrorDomain, NSURLErrorCancelled }.  In some 
 * cases, the task may signal other work before it acknowledges the 
 * cancelation.  -cancel may be sent to a task that has been suspended.
 */

使用同步 API 会很困难；您需要一个异步 API，而调用 cancel 只会产生一个错误，不管出于何种原因都可能发生这种情况，您应该正确处理。