缩放并重新绘制UIScrollView内容后设置contentOffset

Question

I have a UIScrollView that contains a view which redraws itself during zooming. The scaling works great, but setting the contentOffset isn't working. Here is the code

func scrollViewDidZoom(scrollView: UIScrollView) {

    // Get relative position of content view
    let pX = (scrollView.contentOffset.x + scrollView.frame.width / 2.0) / scrollView.contentSize.width
    let pY = (scrollView.contentOffset.y + scrollView.frame.height / 2.0) / scrollView.contentSize.height

    // Rescale and redraw content view        
    contentView.frame=CGRect(x: 0,
        y: 0,
        width: contentView.frame.width * scrollView.zoomScale,
        height: contentView.frame.height * scrollView.zoomScale)
    contentView.scale *= scrollView.zoomScale
    contentView.setNeedsDisplay()

    // Recalculate content offsets so that relative position of content is the same as before
    let nX = contentView.frame.width * pX - scrollView.frame.width / 2.0
    let nY = contentView.frame.height * pY - scrollView.frame.height / 2.0

    // Reset zoom level of scroll view and content offsets
    scrollView.setZoomScale(1.0, animated: false)
    scrollView.setContentOffset(CGPoint(x: nX, y: nY), animated: false)
}

The result is that content view just expands in the positive x and y direction (down and to the right) when it should be zooming in. I've seen some other potential solutions for scrollViewDidEndZooming , but even those aren't working for my case. Any idea where I've gone wrong here?

Answer 1

The problem here was AutoLayout, or rather my use of frames instead of constraints. The problem was solved by a) creating a width constraint property and then editing its constant value when needed, and b) implementing my own zooming behaviour instead of the default UIScrollView 's.