IOS ScrollView Issues

Question

Hey I'm following this tutorial and currently on the first step but am experiencing some weird behavior. The tutorial is on creating scroll views for images and ends with showing how to create a paged horizontal ScrollView with a page controller. I followed the first section and things seemed to be working fine. However when I ran the code it did not perform properly, after about an hour of debugging I downloaded the final project, ran it on my phone to check if it was working correctly (it was) then copied the code into the required files in my project. My project still wouldn't run. So I figured it must be the way in which my story board was configured on the project setup. I then oped the working example cleared their storyboard and created the views and segues my self, in the exact same way and order I had done in my project. Bam! it still worked, when I deleted all views in my story board and recreated them in the exact same fashion, still nothing. Could someone look into this tutorial and tell me if I'm going crazy or they experience similar results. I have narrowed it down to two possibilities, the project provided at the end of the tutorial was created differently and the delegates or outlets were hooked up in a way that only works with the project, or the project was created with an earlier version of the iPhone development kit that works with the current version of XCode but not when I create a new project. Then again I am fairly new to this so I will throw up the code I'm using and hope for the best.

ViewController.h file:

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController <UIScrollViewDelegate>

@property (nonatomic, strong) IBOutlet UIScrollView *scrollView;

@end

ViewController.m file:

#import "ViewController.h"

@interface ViewController ()
@property (nonatomic, strong) UIImageView *imageView;

- (void)centerScrollViewContents;
- (void)scrollViewDoubleTapped:(UITapGestureRecognizer*)recognizer;
- (void)scrollViewTwoFingerTapped:(UITapGestureRecognizer*)recognizer;
@end

@implementation ViewController

@synthesize scrollView = _scrollView;

@synthesize imageView = _imageView;

- (void)centerScrollViewContents {
    CGSize boundsSize = self.scrollView.bounds.size;
    CGRect contentsFrame = self.imageView.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.imageView.frame = contentsFrame;
}

- (void)scrollViewDoubleTapped:(UITapGestureRecognizer*)recognizer {
    // Get the location within the image view where we tapped
    CGPoint pointInView = [recognizer locationInView:self.imageView];
    
    // Get a zoom scale that's zoomed in slightly, capped at the maximum zoom scale specified by the scroll view
    CGFloat newZoomScale = self.scrollView.zoomScale * 1.5f;
    newZoomScale = MIN(newZoomScale, self.scrollView.maximumZoomScale);
    
    // Figure out the rect we want to zoom to, then zoom to it
    CGSize scrollViewSize = self.scrollView.bounds.size;
    
    CGFloat w = scrollViewSize.width / newZoomScale;
    CGFloat h = scrollViewSize.height / newZoomScale;
    CGFloat x = pointInView.x - (w / 2.0f);
    CGFloat y = pointInView.y - (h / 2.0f);
    
    CGRect rectToZoomTo = CGRectMake(x, y, w, h);
    
    [self.scrollView zoomToRect:rectToZoomTo animated:YES];
}

- (void)scrollViewTwoFingerTapped:(UITapGestureRecognizer*)recognizer {
    // Zoom out slightly, capping at the minimum zoom scale specified by the scroll view
    CGFloat newZoomScale = self.scrollView.zoomScale / 1.5f;
    newZoomScale = MAX(newZoomScale, self.scrollView.minimumZoomScale);
    [self.scrollView setZoomScale:newZoomScale animated:YES];
}

- (void)viewDidLoad {
    [super viewDidLoad];
    
    // Set a nice title
    self.title = @"Image";
    
    // Set up the image we want to scroll & zoom and add it to the scroll view
    UIImage *image = [UIImage imageNamed:@"photo1.png"];
    self.imageView = [[UIImageView alloc] initWithImage:image];
    self.imageView.frame = (CGRect){.origin=CGPointMake(0.0f, 0.0f), .size=image.size};
    [self.scrollView addSubview:self.imageView];
    
    // Tell the scroll view the size of the contents
    self.scrollView.contentSize = image.size;
    
    UITapGestureRecognizer *doubleTapRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(scrollViewDoubleTapped:)];
    doubleTapRecognizer.numberOfTapsRequired = 2;
    doubleTapRecognizer.numberOfTouchesRequired = 1;
    [self.scrollView addGestureRecognizer:doubleTapRecognizer];
    
    UITapGestureRecognizer *twoFingerTapRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(scrollViewTwoFingerTapped:)];
    twoFingerTapRecognizer.numberOfTapsRequired = 1;
    twoFingerTapRecognizer.numberOfTouchesRequired = 2;
    [self.scrollView addGestureRecognizer:twoFingerTapRecognizer];
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    
    // Set up the minimum & maximum zoom scales
    CGRect scrollViewFrame = self.scrollView.frame;
    CGFloat scaleWidth = scrollViewFrame.size.width / self.scrollView.contentSize.width;
    CGFloat scaleHeight = scrollViewFrame.size.height / self.scrollView.contentSize.height;
    CGFloat minScale = MIN(scaleWidth, scaleHeight);
    
    self.scrollView.minimumZoomScale = minScale;
    self.scrollView.maximumZoomScale = 1.0f;
    self.scrollView.zoomScale = minScale;
    
    [self centerScrollViewContents];
}

- (void)viewDidUnload
{
    [super viewDidUnload];
    // Release any retained subviews of the main view.
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

- (UIView*)viewForZoomingInScrollView:(UIScrollView *)scrollView
{    
    // Return the view that we want to zoom
    return self.imageView;
}

- (void)scrollViewDidZoom:(UIScrollView *)scrollView
{
    // The scroll view has zoomed, so we need to re-center the contents
    [self centerScrollViewContents];
}

@end

The above code doesn't work as it does in the tutorials project. The following UIScrollView delegate method viewForZoomingInScrollView produces this error:

2013-05-14 10:01:18.585 TestScrollView[3809:907] Made it

May 14 10:01:18 Scott-Laroses-iPhone TestScrollView[3809] : CGAffineTransformInvert: singular matrix.

May 14 10:01:18 Scott-Laroses-iPhone TestScrollView[3809] : CGAffineTransformInvert: singular matrix.

which makes me think the delate isn't properly set up despite me doing it exactly the same as in the tutorial and programmatically when that didn't work. Any ideas?

Answer 1

I figured it out! The issues was that the auto layout constraints were messing up the off screen views. So I disabled auto layout and it worked fine.

Answer 2

Your problem may be from the zoomScale and minimumZoomScale if the value assigned is 0. Make sure that the value is never 0 for those two properties.