如何在 Swift3 中取消 DispatchQueue.main.asyncAfter(deadline: time) ？ [复制]

描述：

我当前正在使用以下代码来查看用户是否已停止在搜索栏中输入内容。我想在每次用户立即开始输入后取消它0.5秒。

Code:

DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
    // your function here
}

问题：

我该如何取消DispatchQueue.main.asyncAfter如果用户开始再次输入Swift3 ?

我尝试过的：

我之前尝试过实施：

NSObject.cancelPreviousPerformRequests(withTarget: self)
self.perform(Selector(("searchForText:")), with: searchString, afterDelay: 0.5)

然而，延迟似乎无法正常工作。

更多代码：

//In class SearchViewController: UITableViewController, UISearchResultsUpdating
func updateSearchResults(for searchController: UISearchController) {
    let searchString: String = searchController.searchBar.text!

    //This is what I previously tried.. which doesn't work...
    //NSObject.cancelPreviousPerformRequests(withTarget: self)
    //self.perform(Selector(("searchForText:")), with: searchString, afterDelay: 0.5)

    //A struct with the first example code shown above.
    Utils.Dispatch.delay(secondsToDelay: 1){
        print("1 second has passed ! " + searchString)
    }
}

对于那些有时间测试代码的人，我将发布我当前未经测试的解决方案。当我有时间尝试时，我会编辑帖子。

private var operationQueue: OperationQueue!
private var mainAsyncQueue: DispatchQueue?


override func viewDidLoad() {
    print("ViewDidLoad of SearchViewController called")

    self.operationQueue = OperationQueue()
    self.currentTime = DispatchTime.now()

}
// MARK: UISearchResultsUpdating

func updateSearchResults(for searchController: UISearchController) {
    let searchStringRaw: String = searchController.searchBar.text!
    let searchString = searchStringRaw.trimmingCharacters(in: .whitespacesAndNewlines)
    guard searchString.characters.count > 0 else {
        return
    }

    print("Search string: \(searchString)")
    self.operationQueue.cancelAllOperations()
    //Put this in Utils.Dispatch.Delay
    self.mainAsyncQueue = DispatchQueue(label: "search.operation." + String(describing: DispatchTime.now()), qos: .default, attributes: DispatchQueue.Attributes.concurrent)

    let time = DispatchTime.now()
    self.currentTime = time

    self.mainAsyncQueue!.asyncAfter(deadline: time + 1){
        guard self.currentTime == time else {
            return
        }

        let tempOperation = BlockOperation(block:{

            if let nsurl: URL = Utils.Url.generate(Constants.Url.Search, options: "&p=1&n=20&q="+searchString.addingPercentEncoding(withAllowedCharacters: .urlHostAllowed)!){
                //Download data and handle response

            } else {
                print("Something went wrong...")
            }


        })
        self.operationQueue.addOperation(tempOperation)
    }

}