正如标题所述，出于某种原因，以下(简化的)代码不起作用:

extension InputView: {

    func updateTable(text: String) {
            NSObject.cancelPreviousPerformRequests(withTarget: self, selector: #selector(loadPlaces(text:)), object: nil)
          //NSObject.cancelPreviousPerformRequests(withTarget: self)

            self.perform(#selector(loadPlaces(text:)), with: text, afterDelay: 0.5)

            prevSearch = inputField.text!;
        }

    //Private wrapper function
    @objc private func loadPlaces(text: String) {
        print("loading results for: \(text)")
       // locator?.searchTextHasChanged(text: text)
    }
}

每次用户编辑 UITextField 时，我都会调用 updateTable，这会调用 localPlaces，后者会调用查询 google 在线位置 API 的函数(评论出去)。不幸的是，在每次调用 updateTable 之后都会调用 loadPlaces 中的打印行。从我的目测来看，打印语句似乎确实有延迟，但是，旧调用不会取消。我尝试查看了很多 StackOverflow 线程，但找不到针对 Swift 3 的任何更新。我是不是调用错了什么？

PS. 如果我改用注释掉的单参数 cancelPreviousPerformRequests。它出于某种原因起作用。

编辑:我已经能够在单独的项目中重现此错误。所以我100%确定上面的代码是错误的。如果您想重现此错误，请打开一个新的 iOS 项目并将以下代码粘贴到默认的 ViewController 中:

class InputView: UIView {

    func updateTable(text: String) {
        NSObject.cancelPreviousPerformRequests(withTarget: self, selector: #selector(loadPlaces(text:)), object: nil)

        self.perform(#selector(loadPlaces(text:)), with: text, afterDelay: 0.5)

    }

    //Private wrapper function
    @objc private func loadPlaces(text: String) {
        print("loading results for: \(text)")
        // locator?.searchTextHasChanged(text: text)
    }
}




class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        let input = InputView()

        for i in 0..<200 {
            input.updateTable(text: "Call \(i)")
        }
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}

最佳答案

Duncan C 的回答中的解释不适用于这种情况。

在 cancelPreviousPerformRequests(withTarget:selector:object:) 的引用文献中:

Discussion

All perform requests are canceled that have the same target as aTarget, argument as anArgument, and selector as aSelector.

所以，当你有这样一行时:

<aTarget>.perform(<aSelector>, with: <anArgument>, afterDelay: someDelay)

您可以通过以下方式取消它:

NSObject.cancelPreviousPerformRequests(withTarget: <aTarget>, selector: <aSelector>, object: <anArgument>)

仅当 aTarget、aSelector 和 anArgument 全部匹配时。

请尝试这样的事情并检查你看到了什么:

class InputView: UIView {
    
    var lastPerformArgument: NSString? = nil
    
    func updateTable(text: String) {
        NSObject.cancelPreviousPerformRequests(withTarget: self, selector: #selector(loadPlaces(text:)), object: lastPerformArgument)

        lastPerformArgument = text as NSString
        self.perform(#selector(loadPlaces(text:)), with: lastPerformArgument, afterDelay: 0.5)
        
    }
    
    //Private wrapper function
    @objc private func loadPlaces(text: String) {
        print("loading results for: \(text)")
        // locator?.searchTextHasChanged(text: text)
    }
}

关于ios - cancelPreviousPerformRequests 似乎在 Swift 3.0 中不起作用，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/43983134/