UIScrollView Zooming Crashes App with Exc_Bad_Access - iphone

Question

I am getting a Exc_Bad_Access error in main when I try to scroll my UIScrollView. This program is simple. I have A UIViewController added in AppDelegate. Then, here is the code in the ViewController. This works fine for scrolling but as soon as I add tmpScrollView.delegate = self. The program won't scroll or zoom and gives me the Exc_Bad_Access error when I try to zoom.
#interface MainViewController : UIViewController &ltUIScrollViewDelegate>
#property (nonatomic,retain) UIScrollView *tmpScrollView;
#property (nonatomic,retain) UIView *containerView;
#end
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view.
tmpScrollView = [[UIScrollView alloc] initWithFrame:self.view.frame];
tmpScrollView.delegate = self;
[self.view addSubview:tmpScrollView];
// Set up the container view to hold our custom view hierarchy
CGSize containerSize = CGSizeMake(640.0f, 640.0f);
self.containerView = [[UIView alloc] initWithFrame:(CGRect){.origin=CGPointMake(0.0f, 0.0f), .size=containerSize}];
[self.tmpScrollView addSubview:self.containerView];
// Set up custom view hierarchy
UIView *redView = [[UIView alloc] initWithFrame:CGRectMake(0.0f, 0.0f, 640.0f, 80.0f)];
redView.backgroundColor = [UIColor redColor];
[self.containerView addSubview:redView];
UIView *blueView = [[UIView alloc] initWithFrame:CGRectMake(0.0f, 560.0f, 640.0f, 80.0f)];
blueView.backgroundColor = [UIColor blueColor];
[self.containerView addSubview:blueView];
UIView *greenView = [[UIView alloc] initWithFrame:CGRectMake(160.0f, 160.0f, 320.0f, 320.0f)];
greenView.backgroundColor = [UIColor greenColor];
[self.containerView addSubview:greenView];
UIImageView *imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:#"slow.png"]];
imageView.center = CGPointMake(320.0f, 320.0f);
[self.containerView addSubview:imageView];
//Tell the scroll view the size of the contents
self.tmpScrollView.contentSize = containerSize;
}
-(void)viewWillAppear:(BOOL)animated
{
NSLog(#"Will Appear");
[super viewWillAppear:animated];
// Set up the minimum & maximum zoom scales
CGRect scrollViewFrame = self.tmpScrollView.frame;
CGFloat scaleWidth = scrollViewFrame.size.width / self.tmpScrollView.contentSize.width;
CGFloat scaleHeight = scrollViewFrame.size.height / self.tmpScrollView.contentSize.height;
CGFloat minScale = MIN(scaleWidth, scaleHeight);
self.tmpScrollView.minimumZoomScale = minScale;
self.tmpScrollView.maximumZoomScale = 1.0f;
self.tmpScrollView.zoomScale = minScale;
//***** Here is the line for setting the delegate
self.tmpScrollView.delegate = self;
[self centerScrollViewContents];
}
-(void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale
{
NSLog(#"End Zoom");
}
-(UIView*)viewForZoomingInScrollView:(UIScrollView *)scrollView {
// Return the view that we want to zoom
return self.containerView;
}
-(void)scrollViewDidZoom:(UIScrollView *)scrollView {
// The scroll view has zoomed, so we need to re-center the contents
[self centerScrollViewContents];
}
#end
Thanks for any help. This has been driving me crazy for a day now...
Edit: Adding centerScrollViewContens too:
- (void)centerScrollViewContents {
CGSize boundsSize = self.tmpScrollView.bounds.size;
CGRect contentsFrame = self.containerView.frame;
if (contentsFrame.size.width < boundsSize.width) {
contentsFrame.origin.x = (boundsSize.width - contentsFrame.size.width) / 2.0f;
} else {
contentsFrame.origin.x = 0.0f;
}
if (contentsFrame.size.height < boundsSize.height) {
contentsFrame.origin.y = (boundsSize.height - contentsFrame.size.height) / 2.0f;
} else {
contentsFrame.origin.y = 0.0f;
}
self.containerView.frame = contentsFrame;
}

Answer 1

Whatever Code you have provided is working fine on my end.May be there could be some sort of problem in your "centerScrollViewContents" method.Can you post the code for this method also???

Answer 2

You need to work out the minimum zoom scale for the scroll view. A zoom scale of one means that the content is displayed at normal size. A zoom scale below one shows the content zoomed out, while a zoom scale of greater than one shows the content zoomed in. To get the minimum zoom scale, you calculate how far you’d need to zoom out so that the image fits snugly in your scroll view’s bounds based on its width. Then you do the same based upon the image’s height. The minimum of those two resulting zoom scales will be the scroll view’s minimum zoom scale. That gives you a zoom scale where you can see the entire image when fully zoomed out.
Swift:
let scrollViewFrame = scrollView.frame
let scaleWidth = scrollViewFrame.size.width / scrollView.contentSize.width
let scaleHeight = scrollViewFrame.size.height / scrollView.contentSize.height
let minScale = min(scaleWidth, scaleHeight);
scrollView.minimumZoomScale = minScale;
Objective-C
CGFloat scrollViewFrame = scrollView.frame
CGFloat scaleWidth = scrollViewFrame.size.width / scrollView.contentSize.width
CGFloat scaleHeight = scrollViewFrame.size.height / scrollView.contentSize.height
CGFloat minScale = min(scaleWidth, scaleHeight);
scrollView.minimumZoomScale = minScale;
From other projects and personal experience doing heavy GPU on the iOS (endless scroll, maximum bitmap size, etc), I've noticed that each device has it's own threshold. For past projects, I've also hardcoded the below values as the minimumZoomScale to prevent the crashes:
scale :
{
iPad : {
min : 0.8
, max : 1.6
}
, iPhone : {
min : 0.25
, max : 1.6
}
, iPhone6 : {
min : 0.3333
, max : 1.6
}
, iPhoneResizable: {
min : 1
, max : 1.6
}
}
Great tutorial for beginners: http://www.raywenderlich.com/76436/use-uiscrollview-scroll-zoom-content-swift