Resetting UIScrollView's zoomScale property on autorotation - iphone

Question

I have a custom UIViewController onto which I've added a UIImageView (on the StoryBoard) and then embedded the UIImageView in a UIScrollView. My program loads an image into the imageView and scales it to properly fit. By proper fit, I mean this:
if the aspect ratio of the image exactly matches that of the view, the image will be scaled to exactly fit the view, with no scroll bars
otherwise, the image will be scaled to exactly fit in one dimension, with a scrollbar in the other dimension.
I currently do this in viewWillAppear. Below is my code for that method and an auxiliary method that calculates the correct zoomScale:
-(float) findZoomScale {
float widthRatio = self.view.bounds.size.width / self.imageView.image.size.width;
float heightRatio = self.view.bounds.size.height / self.imageView.image.size.height;
float ratio;
if (widthRatio > heightRatio) ratio = widthRatio;
else ratio = heightRatio;
return ratio;
}
- (void) viewWillAppear:(BOOL)animated {
[super viewWillAppear:YES];
self.imageView.image = self.image;
self.imageView.frame = CGRectMake(0, 0, self.imageView.image.size.width, self.imageView.image.size.height);
self.scrollView.contentSize = self.imageView.image.size;
self.scrollView.zoomScale = [self findZoomScale];
[self.scrollView flashScrollIndicators];
}
- (void)viewDidLoad {
[super viewDidLoad];
self.image = [UIImage imageWithData:[NSData dataWithContentsOfURL:self.photoURL]];
self.imageView.image = self.image;
self.imageView.frame = CGRectMake(0, 0, self.imageView.image.size.width,
self.imageView.image.size.height);
self.scrollView.delegate = self;
self.scrollView.zoomScale = 1.0;
self.navigationItem.title = self.photoTitle;
self.scrollView.autoresizesSubviews = YES;
self.scrollView.autoresizingMask = (UIViewAutoresizingFlexibleBottomMargin |
UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleLeftMargin |
UIViewAutoresizingFlexibleTopMargin | UIViewAutoresizingFlexibleWidth |
UIViewAutoresizingFlexibleHeight);
}
This code works as I intended for the initial load of an image, whether the iPhone is in landscape or portrait orientation. But when I then rotate the iPhone with the image already loaded, it does not properly rescale. I have tried to do the rescaling in didRotateFromInterfaceOrientation, playing with the scrollView's zoomScale property, but I can't get it to work. Is this the correct place to do the rescaling? And if so, how do I do it? Thanks.
Duane

Answer 1

I just had this exact problem (I assume you're on the CS193p assignment 4 as well), and solved it by setting the zoomScale back to 1 before adjusting the UIScrollView's contentSize upon rotation.
For example:
- (void)willAnimateRotationToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration
{
//reset zoomScale back to 1 so that contentSize can be modified correctly
self.scrollView.zoomScale = 1;
// reset scrolling area equal to size of image
self.scrollView.contentSize = self.imageView.image.size;
//reset the image frame to the size of the image
self.imageView.frame = CGRectMake(0, 0, self.imageView.image.size.width, self.imageView.image.size.height);
//set the zoomScale to what we actually want
self.scrollView.zoomScale = [self findZoomScale];
}

Answer 2

You can use
-(void)viewWillLayoutSubviews
in your UIViewController. This will get called whenever the view is loaded/rotated/resized.