当applicationWillEnterForeground发生时验证剪贴板(swift)

您可以像这样检查剪贴板上的图像:

override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)
    if UIPasteboard.generalPasteboard().image != nil {
        pasteButton.enabled = true
    } 
    else {
        pasteButton.enabled = false
    }
}

如果要使用该事件,可以执行以下操作:

override func viewDidLoad() {
    super.viewDidLoad()
    NSNotificationCenter.defaultCenter().addObserver(self, 
    selector: Selector("updatePasteButton"), 
    name: UIApplicationWillEnterForegroundNotification, 
    object: nil)
}

func updatePasteButton() {
    if UIPasteboard.generalPasteboard().image != nil {
        pasteButton.enabled = true
    } 
    else {
        pasteButton.enabled = false
    }
}

updatePasteButton()将在每次事件发生时被调用。