setContentOffset loses precision? - iphone

Question

I have an application where I need to initialize the contentOffset of a UIScrollView to a certain value. I notice when I set the contentOffset, it rounds the points up to the nearest integers. I've tried using both setContentOffset and setContentOffset:animated and still get the same result. When I try to manually add the contentOffset onto the frame origin, I don't get the result I want. Anyone know anyway around this?
UIScrollView *myScrollViewTemp = [[UIScrollView alloc] initWithFrame: CGRectMake(CropThePhotoViewControllerScrollViewBorderWidth, CropThePhotoViewControllerScrollViewBorderWidth, self.myScrollViewBorderView.frame.size.width - (CropThePhotoViewControllerScrollViewBorderWidth * 2), self.myScrollViewBorderView.frame.size.height - (CropThePhotoViewControllerScrollViewBorderWidth * 2))];
[self setMyScrollView: myScrollViewTemp];
[[self myScrollView] setAutoresizingMask: UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight];
[[self myScrollView] setShowsVerticalScrollIndicator: NO];
[[self myScrollView] setShowsHorizontalScrollIndicator: NO];
[[self myScrollView] setBouncesZoom: YES];
[[self myScrollView] setDecelerationRate: UIScrollViewDecelerationRateFast];
[[self myScrollView] setDelegate:self];
[[self myScrollViewBorderView] addSubview: [self myScrollView]];
[myScrollViewTemp release];
UIImageView *myImageViewTemp = [[UIImageView alloc] initWithImage: self.myImage];
[self setMyImageView: myImageViewTemp];
[[self myScrollView] addSubview:[self myImageView]];
[[self myScrollView] setContentSize: [self.myImage size]];
[[self myScrollView] setMinimumZoomScale: self.previousZoomScale];
[[self myScrollView] setMaximumZoomScale: 10];
[[self myScrollView] setZoomScale: self.previousZoomScale animated:NO];
[[self myScrollView] setContentOffset: self.contentOffset animated:NO];
[myImageViewTemp release];
UPDATE: Updated code.

Answer 1

It appears this isn't a bug on my part, but is the intended behavior by Apple whether on purpose or not. In order to work around this, you need to set the contentOffset in the viewWillLayoutSubviews method of the UIViewController. Apparently, you need to set the contentOffset after the whole view frame has been set.

Answer 2

I too struggled with this issue quite a bit, but it turns out that you could just set the bounds on the scroll view, which does the same thing and actually deals ok with CGFloat values.
CGPoint newOffset = CGPointMake(3.8, 0);
We got the new offset here.
[scrollView setContentOffset:newOffset];
After this line the current offset is (4,0).
scrollView.bounds = CGRectMake(newOffset.x, newOffset.y, scrollView.bounds.size.width, scrollView.bounds.size.height);
And this gives you (3.8, 0)

Answer 3

Swift 4:
I've maded an extension to have more precision:
extension UIScrollView {
func setPreciseContentOffset( x:CGFloat? = nil, y:CGFloat? = nil, animated:Bool,completion:#escaping ((Bool) -> Void)) {
var myX:CGFloat = self.contentOffset.x
var myY:CGFloat = self.contentOffset.y
if let x = x {
myX = x
}
if let y = y {
myY = y
}
let point = CGPoint(x:myX,y:myY)
if animated {
// calculate duration
var duration = 0.25 // min duration
let destCoord = myX != self.contentOffset.x ? myX : myY
let diff = fabs ( self.contentOffset.x - destCoord)
duration += TimeInterval(diff) / 1000
UIView.animate(withDuration:duration, delay: 0.0, options: [.curveEaseInOut], animations: {
self.bounds = CGRect(x:point.x,y:point.y,width: self.bounds.size.width,height: self.bounds.size.height)
}, completion: { (finished: Bool) in
completion(finished)
})
} else {
self.bounds = CGRect(x:point.x,y:point.y,width: self.bounds.size.width,height: self.bounds.size.height)
completion(true)
}
}
}
Usage:
// supposing you have to scroll manually in horizontal
self.myScrollview.setPreciseContentOffset(x:contentX, animated: true, completion: {[weak self] _ in
guard let `self` = self else { return }
// HERE the scroll is ended, pay attention the end scrolling delegates aren't be called because you set manually self.bounds so HERE implement your scrolling end code
})

Answer 4

I think this is because the contents of any subviews of the UIScrollView would be rendered blurred if the contentOffset is not rounded up, especially text.