Animate multiple UIViews alpha - ios

Question

I have multiple labels placed on scroll view like:
private func drawDates(_ multiplier: Double){
contentView.subviews.forEach{it in
it.removeFromSuperview()
}
let maximumVisibleDates = 6.0
let dateLabelOffset = Double(UIScreen.main.bounds.size.width / CGFloat(maximumVisibleDates))
let doublePoints = data.findClosestDatePointsForInterval(interval: dateLabelOffset,
multiplier: multiplier)
print(doublePoints)
let datesToShow = data.datesForPoints(points: doublePoints, multiplier: multiplier)
for (index, value) in datesToShow.enumerated(){
if index == datesToShow.count - 1 {
continue
}
let label = UILabel.init(frame: CGRect.init(x: CGFloat(doublePoints[index]),
y: Dimensions.chartHeight.value + Offsets.small.value,
width: Dimensions.dateLabelWidth.value,
height: Dimensions.dateLabelHeight.value))
label.text = redableString(value)
label.font = UIFont.systemFont(ofSize: FontSizes.yLabel.value)
label.textColor = Settings.isLightTheme() ? Colors.LightTheme.textGray.value : Colors.DarkTheme.textGray.value
label.sizeToFit()
contentView.addSubview(label)
}
}
When i call:
contentView.subviews.forEach{it in
it.removeFromSuperview()
}
Actually i want to fade "old" labels from old function call and then add new labels animated. How to do that?

Answer 1

There are 3 ways to remove old view and add new view with animation.
Solution 1:
Set new view alpha to 0 and add it to super view.
Do animation.
Remove old view after animation.
In this case, use for loop in animations block to set alpha, and in completion block to remove old views.
let viewToAdd = ...
viewToAdd.alpha = 0
contentView.addSubview(viewToAdd)
UIView.animate(withDuration: 1, animations: {
viewToRemove.alpha = 0
viewToAdd.alpha = 1
}, completion: { (_) in
viewToRemove.removeFromSuperview()
})
Solution 2:
Call transition(with:duration:options:animations:completion:) method. Use .transitionCrossDissolve as options value.
In this case, use for loop in animations block to remove old views and add new views.
UIView.transition(with: contentView,
duration: 1,
options: .transitionCrossDissolve,
animations: {
viewToRemove.removeFromSuperview()
contentView.addSubview(viewToAdd)
}, completion: nil)
Solution 3:
If the number of old views is equal to the number of new views, call transition(from:to:duration:options:completion:) method. Use .transitionCrossDissolve as options value.
In this case, use for loop to call the method.
UIView.transition(from: viewToRemove,
to: viewToAdd,
duration: 1,
options: .transitionCrossDissolve,
completion: nil)

Answer 2

You could leverage the UIView animation API:
https://developer.apple.com/documentation/uikit/uiview/1622515-animatewithduration