swift - 如何只移动一次标签(快速)？

Question

我以编程方式创建了一个标签，最初标签没有出现，只有当按钮“出现”被触摸时(确定)。我想知道如何只移动标签一次。如果标签是第一次移动，当我再次触摸按钮时，一定不会发生任何事情。

import UIKit

class ViewController: UIViewController {

var label = UILabel()
var screenWidth: CGFloat = 0.0
var screenHeight: CGFloat = 0.0

override func viewDidLoad() {
    super.viewDidLoad()

    let screenSize: CGRect = UIScreen.mainScreen().bounds
    screenWidth = screenSize.width
    screenHeight = screenSize.height

    label = UILabel(frame: CGRectMake(0, 64, screenWidth, 70))
    label.textAlignment = NSTextAlignment.Center
    label.backgroundColor = UIColor.blackColor()
    label.text = "Label Appear"
    label.font = UIFont(name: "HelveticaNeue-Bold", size: 16.0)
    label.textColor = UIColor.whiteColor()
    view.addSubview(label)


    // Do any additional setup after loading the view, typically from a nib.
}

override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)

    self.label.center.y -= self.view.bounds.width


}
@IBAction func appear(sender: AnyObject) {

    UIView.animateWithDuration(0.5, animations: {

        self.label.center.y += self.view.bounds.width

        }, completion: nil)
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}


}

Answer 1

一种解决方案是添加一个 bool 值，指示标签是否已经移动。

例如:

var hasLabelAlreadyMoved = false
...
@IBAction func appear(sender: AnyObject) {

/* 
We want to move the label if the bool is set to false ( that means it hasn't moved yet ), 
else ( the label has already moved ) we exit the function 
*/
guard !self.hasLabelAlreadyMoved else { 
   return 
}

self.hasLabelAlreadyMoved = true 
UIView.animateWithDuration(0.5, animations: {

    self.label.center.y += self.view.bounds.width

    }, completion: nil)
}