How can I use scrollRectToVisible to scroll to the center of the image?

Question

I have a UIScrollView with zooming and panning. I want the image to scroll to the center after the user command. My problem is calculating the size and location of the frame that is in the center of the image.

Does anyone know how to calculate the correct frame for the center of my image? The problem is that if the scale is scaled, the frame changes.

Thank!

Answer 1

The code might be a little better here in case someone needs it ,-)

UIScrollView + CenteredScroll.h:

@interface UIScrollView (CenteredScroll)

-(void)scrollRectToVisibleCenteredOn:(CGRect)visibleRect
                            animated:(BOOL)animated;

@end

UIScrollView + CenteredScroll.m:

@implementation UIScrollView (CenteredScroll)

-(void)scrollRectToVisibleCenteredOn:(CGRect)visibleRect
                            animated:(BOOL)animated
{
  CGRect centeredRect = CGRectMake(visibleRect.origin.x + visibleRect.size.width/2.0 - self.frame.size.width/2.0,
                                   visibleRect.origin.y + visibleRect.size.height/2.0 - self.frame.size.height/2.0,
                                   self.frame.size.width,
                                   self.frame.size.height);
  [self scrollRectToVisible:centeredRect
                   animated:animated];
}

@end

Answer 2

, , :

@implementation UIScrollView (jsCenteredScroll)

-(void)jsScrollRectToVisibleCenteredOn:(CGRect)visibleRect
                            animated:(BOOL)animated
{

    CGPoint center = visibleRect.origin;
    center.x += visibleRect.size.width/2;
    center.y += visibleRect.size.height/2;

    center.x *= self.zoomScale;
    center.y *= self.zoomScale;


    CGRect centeredRect = CGRectMake(center.x - self.frame.size.width/2.0,
                                     center.y - self.frame.size.height/2.0,
                                     self.frame.size.width,
                                     self.frame.size.height);
    [self scrollRectToVisible:centeredRect
                     animated:animated];
}

@end

Answer 3

private func centerScrollContent() {
    let x = (imageView.image!.size.width * scrollView.zoomScale / 2) - ((scrollView.bounds.width) / 2)
    let y = (imageView.image!.size.height * scrollView.zoomScale / 2) - ((scrollView.bounds.height) / 2)
    scrollView.contentOffset = CGPointMake(x, y)
}

Answer 4

Ok, earned it. Here's the code anyone needs:

CGFloat tempy = imageView.frame.size.height;
CGFloat tempx = imageView.frame.size.width;
CGRect zoomRect = CGRectMake((tempx/2)-160, (tempy/2)-240, myScrollView.frame.size.width, myScrollView.frame.size.height);
[myScrollView scrollRectToVisible:zoomRect animated:YES];