如果我的应用程序在整个运行时都使用它，它应该如何处理当前日期？

Question

我应该在哪里放置 Date 实例以及我应该如何处理调用它以获得当前日期？我应该用日期实例创建一个单例吗？我是否应该在 AppDelegate 的功能之一中调用此实例，以便在应用程序未使用时更新当前日期？

Answer 1

"Where should I put a Date instance and how should I handle calling it in order to get the current date? " 在您当前的 View Controller 中就足够了。只要 VC 还活着，它对您的 Date 对象有很强的引用。

"Should I make a singleton with a date instance?" 不。如果你需要保持日期相关，你需要触发一个计时器（比如 1 分钟所以它不会打扰太多）这将使 UI

中的日期更新

"Should I call this instance in one of AppDelegate's functions in order to update the current date when the app isn't on use?" 不，您可以获得通知，并通过它们知道何时启动或关闭计时器。见代码

class ViewController: UIViewController{
// label to hold the date
@IBOutlet var dateLabel: UILabel!

// timer to keep it updated
var fetchTimer: Timer!

override func viewDidLoad()
{
    super.viewDidLoad()

    // set date immediately (dont wait for timer)
    viewDidEnterForeground()

    // follow Foreground so when we re-enter, timer will launch again
    NotificationCenter.default.addObserver(self,
                                           selector: #selector(ViewController.viewDidEnterForeground),
                                           name:NSNotification.Name.UIApplicationWillEnterForeground,
                                           object: nil)

    // follow background for invalidating timer
    NotificationCenter.default.addObserver(self,
                                           selector: #selector(ViewController.viewDidEnterBackground),
                                           name:NSNotification.Name.UIApplicationDidEnterBackground,
                                           object: nil)
}
// on each entry - set date and fire timer
func viewDidEnterForeground()
{
    setDate()

    fetchTimer = Timer.scheduledTimer(timeInterval: 60.0,
                                      target: self,
                                      selector: #selector(timerFunc),
                                      userInfo: nil,
                                      repeats: true)
}
func viewDidEnterBackground()
{
    fetchTimer.invalidate()
}
func timerFunc()
{
    setDate()
}
func setDate()
{
    let date = Date()

    let formatter = DateFormatter()
    formatter.dateFormat = "dd.MM.yyyy"

    // "22.04.2017"
    let dateFormatString = formatter.string(from: date)

    DispatchQueue.main.async
    {
        self.dateLabel.text = dateFormatString
    }
}
deinit
{
    NotificationCenter.default.removeObserver(self, name:NSNotification.Name.UIApplicationWillEnterForeground, object: nil)

    NotificationCenter.default.removeObserver(self, name:NSNotification.Name.UIApplicationDidEnterBackground, object: nil)
}
}

Answer 2

你的问题部分没有真正意义：

"Where should I put a Date instance and how should I handle calling it in order to get the current date?"

Date 实例记录了一个固定的时间点。代码

let date = Date()

会在调用的那一刻记录当前日期，不会改变。如果您的计划明天仍然是运行，那么该日期现在将非常 "out of date"。

相反，您应该在任何需要当前日期的时候使用表达式 Date()。

如果我的应用程序在整个运行时都使用它，它应该如何处理当前日期？

How should my app handle the current date if it uses it throughout its runtime?

nsdate

ios

swift