Weird Button Animation - ios

Question

It's my first try on IOS animation, so if I'm worry from the very beginning, just tell me the right direction.
All I want: when I click ButtonOne, Label disappears slowly.
The code as below:
import UIKit
class ViewController: UIViewController {
#IBOutlet weak var labelHeight: NSLayoutConstraint!
private var isHidden: Bool = false
#IBAction func clickButtonOne(sender: UIButton) {
isHidden = !isHidden
if isHidden {
labelHeight.constant = 0
} else {
labelHeight.constant = 60
}
UIView.animateWithDuration(1.0, animations: {
() -> Void in
self.view.layoutIfNeeded()
}, completion: nil)
}
override func viewDidLoad() {
super.viewDidLoad()
}
}
Before I click ButtonOne:
After I click ButtonOne(label shrinks from bottom to top):

Answer 1

The UILabel is disappearing, but it's content is still visible.
You need to set the clipsToBounds property of the UILabel to true.
label.clipsToBounds = true
You can set the same property in the interface builder by checking the Clip Subviews property in the attributes inspector.

Answer 2

I think you should also animate UIView.alpha property:
import UIKit
class ViewController: UIViewController {
#IBOutlet weak var button: UIButton!
#IBOutlet weak var labelHeight: NSLayoutConstraint!
private var isHidden: Bool = false
#IBAction func clickButtonOne(sender: UIButton) {
isHidden = !isHidden
var alpha: CGFloat = 1
if isHidden {
alpha = 0
labelHeight.constant = 0
} else {
labelHeight.constant = 60
}
UIView.animateWithDuration(1.0, animations: {
() -> Void in
self.button.alpha = alpha
self.view.layoutIfNeeded()
}, completion: nil)
}
override func viewDidLoad() {
super.viewDidLoad()
}
}