UIPickerView freeze UI

Question

在我的应用程序中，我有一个包含两个组件的ViewController :一个像时钟一样供用户使用的UILabel和一个允许用户选择项目的UIPickerView。

下面是代码：

class MyView: UIViewController, UIPickerViewDelegate, UIPickerViewDataSource{

@IBOutlet weak var lblClock: UILabel!
@IBOutlet weak var pickerAttendance: UIPickerView!
var timer : Timer!
var dateTime: Date!
var pickerData: [String] = ["a","b","c"]

   override func viewDidLoad() {
        super.viewDidLoad()

        dateTime = Date()
        timer = Timer.scheduledTimer(timeInterval: TimeInterval(1), target: self, selector: #selector(updateDate), userInfo: nil, repeats: true)
        timer.fire()

        pickerAttendance.delegate = self
        pickerAttendance.dataSource = self
   }

    @objc func updateDate(){
        dateTime = NSCalendar.current.date(byAdding: Calendar.Component.second, value: 1, to: self.dateTime)
        let s = DateFormatter.localizedString(from: self.dateTime, dateStyle: DateFormatter.Style.none, timeStyle: DateFormatter.Style.medium)
        DispatchQueue.main.async {
            self.lblClock.text = s
        }
    }

   func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
   }

   func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return pickerData.count
   }

   func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        return pickerData[row]
   }
}

我用实际值实例化了一个日期和一个计时器，函数每秒钟更新一次标签的值。我解释了我的问题:当我滚动选择器视图时，带有计时器的标签没有更新，但当我松开滚动条时，标签开始更新。

scrool冻结用户界面。

我已经尝试在主线程中更新标签，但仍然出现问题。我希望当我分析选取器视图时，标签将继续更新。

Answer 1

把你的计时器放在run循环中：

override func viewDidLoad() {
    super.viewDidLoad()

    dateTime = Date()
    timer = Timer.scheduledTimer(timeInterval: TimeInterval(1), target: self, selector: #selector(updateDate), userInfo: nil, repeats: true)

    RunLoop.main.add(timer, forMode: RunLoop.Mode.common)

    timer.fire()

    pickerAttendance.delegate = self
    pickerAttendance.dataSource = self
}