如何通过动画向下移动视图？

Question

In my app, I implement webview, and under that webview I have a one view and I want to move that view by animation like in Safari.

Here is my code:

func scrollViewWillBeginDragging(scrollView: UIScrollView) {
    if scrollView.panGestureRecognizer.translationInView(scrollView.superview).y > 0 {
        // scrolls down
        print("UP")
        viewbottom.hidden = false
        viewHieght.constant = 45
    } else {
        print("DOWN")
        viewbottom.hidden = true
        viewHieght.constant = 0
    }
}

In this code I am hiding the view while scroll down but I want to move it down slowly like Safari. So how can I do this?

Answer 1

use layoutIfNeeded() property with animateWithDuration

   UIView.animateWithDuration(0.2, animations: { () -> Void in
        viewHieght.constant = 45
        self.view.layoutIfNeeded()
   })

Answer 2

viewHeight.constant = max(0, min(45, scrollView.panGestureRecognizer.translationInView(scrollView.superview).y))

这应该使视图随手势移动，但min为0，max为45