How can I use scrollRectToVisible to scroll to the center of an image?
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18-09-2019 - |
Question
I have a UIScrollView with zooming and panning. I want the image to scroll to the center after a user command. My problem is in calculating the size and location of a 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 zoomScale is different the frame changes.
Thanks!
Solution
Here's maybe a bit better code in case anyone is in need ;-)
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
OTHER TIPS
Based on Daniel Bauke answer, I updated his code to include zoom scale :
@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
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)
}
Okay, got it working. Here's the code incase anyone is in need:
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];
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