* i have programmed a bars graph when each bar is uiview with constraints on it's height and top constraint to the superview.Once they get values i perform an animation with 10 seconds duration. However, the animation is displayed very fast.

tried to set needs layout for the superview

// calculating the new height of the bar

      let portion = Float(self.currentValue!) / Float(self.maxValue!) // portion of max height of the bar
        let newTopConstraint =  Float(maxTopConstraint) * portion // the new distance from the top of the superview

var heightDiff = newTopConstraint - Float(self.barTopConstraint.constant)
        if (heightDiff < 0 ) {
            heightDiff = heightDiff * -1
        }

UIView.animate(withDuration: 10, animations: {[self] in
            self.barTopConstraint.constant = CGFloat(newTopConstraint)
            self.heightCons.constant += CGFloat(heightDiff)
           self.barView.setNeedsLayout()
            })

i except the bars  to rise in the correct speed.*