ios - 进入 View 时更新特定的 ViewController

Question

我有两个 UIViewController，每当它们出现时我都想更新它们。

In DashBordViewControlller I have therefore added this code:

override func viewDidLoad() {
    super.viewDidLoad()

    let appDelegate:AppDelegate = UIApplication.sharedApplication().delegate! as AppDelegate
    appDelegate.dashboardViewController = self

and in DetailViewController this code:

override func viewDidLoad() {
    super.viewDidLoad()

    let appDelegate:AppDelegate = UIApplication.sharedApplication().delegate! as AppDelegate
    appDelegate.detailViewController = self

In AppDelegate I have added this code:

class AppDelegate: UIResponder, UIApplicationDelegate {

var window: UIWindow?

var dashboardViewController:DashboardViewController?
var detailViewController:DetailViewController?

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    return true
}

func applicationWillResignActive(application: UIApplication) {
  }

func applicationDidEnterBackground(application: UIApplication) {
     println("Goodbye world")
}

func applicationWillEnterForeground(application: UIApplication) {
    println("Hello again world")
    dashboardViewController?.cleanCDandQueryHKLoop()
    detailViewController?.rememberWhatSegmentIsPressed()
}

我的问题是，只要有一个 ViewController 进入 View ，两个 UIViewControllers 都会更新。例如，如果我关闭应用程序(主页)然后重新打开它。

我如何在 AppDelegate 中检查哪个 ViewController 进入 View 并只更新那个？任何帮助将不胜感激 - 谢谢!

Answer 1

您应该像这样在 View Controller 的 viewWillAppear 中添加一个观察者:

override func viewWillAppear(animated: Bool) {
  super.viewWillAppear(animated)
  NSNotificationCenter.defaultCenter().addObserver(self, selector: "willEnterForeground:", name: UIApplicationWillEnterForegroundNotification, object: nil)
}

之后，实现你的功能:

func willEnterForeground(notification: NSNotification!) {
  // View Controller is brought to Foreground
}

哦，别忘了移除 viewWillDisappear 上的观察者:

override func viewWillDisappear(animated: Bool) {
  super.viewWillDisappear(animated)
  NSNotificationCenter.defaultCenter().removeObserver(self, name: nil, object: nil)
}