检测用户在Swift中停止/暂停键入的时间

Question

我已经挖掘了stackoverflow并找到了我转换为Swift的解决方案,它似乎不起作用,选择器仍在执行.

 func searchBar(searchBar: UISearchBar, textDidChange searchText: String) {
    self.filter.searchTerm = self.searchBar.text

    NSObject.cancelPreviousPerformRequestsWithTarget(self, selector: "getHints", object: nil)
    NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: "getHints", userInfo: nil, repeats: false)
}

在swift中有更好的方法吗？谢谢!

Answer 1

更新2016/09/01:

我们可以使用NSTimers或(自swift 2.0)NSObject performSelector和朋友.

Aproach 1: performSelector

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange,
    replacementString string: String) -> Bool {
    NSObject.cancelPreviousPerformRequests(
        withTarget: self,
        selector: #selector(ViewController.getHintsFromTextField),
        object: textField)
    self.perform(
        #selector(ViewController.getHintsFromTextField),
        with: textField,
        afterDelay: 0.5)
    return true
}

func getHintsFromTextField(textField: UITextField) {
    print("Hints for textField: \(textField)")
}

方法2: NSTimer

var timer: NSTimer? = nil

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange,
    replacementString string: String) -> Bool {
    timer?.invalidate()
    timer = Timer.scheduledTimer(
        timeInterval: 0.5,
        target: self,
        selector: #selector(ViewController.getHints),
        userInfo: ["textField": textField],
        repeats: false)
    return true
}

func getHints(timer: Timer) {
    var userInfo = timer.userInfo as! [String: UITextField]
    print("Hints for textField: \(userInfo["textField"])")
}

注意我正在传递textField延迟函数.它并不总是必需的,但是当textField它不容易访问或处理各种文本字段时,它可以使您的生活更轻松.

如何NSTimer方法是从不同performSelector？

当你调用performSelector目标时,保留目标(在swift中,目标始终是self),但是当你使用NSTimer目标时不保留.这意味着,如果你使用NSTimers,你必须确保self在计时器触发时目标(在这种情况下)是活着的.否则会发生崩溃.

(BTW:内部performSelector使用NSTimer)

如果你对GCD计时器感兴趣,那么这个要点就是一个好的开始: maicki/TimerWithGCD.md