Cannot pan UIScrollView after zooming

Question

I've programatically created a UIScrollView using the following code:

.h:

@interface MainController : UIViewController <UIScrollViewDelegate>

@property (nonatomic, retain) UIScrollView *mainScrollView;
@property (nonatomic, retain) UIView *mainView;

.m:

- (void) initVariables
{
    // Setters

    screenRect = [[UIScreen mainScreen] bounds];
    screenWidth = screenRect.size.width;
    screenHeight = screenRect.size.height;

    // Alloc-init methods
    mainScrollView = [[UIScrollView alloc] init];
    mainView = [[UIView alloc] init];
}

- (void) setUpScrollView
{
    mainScrollView.frame = CGRectMake(0.0f, 0.0f, screenWidth, screenHeight);
    mainScrollView.contentSize = CGSizeMake(screenWidth*2, screenHeight*2);
    mainScrollView.minimumZoomScale = 1.0;
    mainScrollView.maximumZoomScale = 4.0;
    mainScrollView.backgroundColor = [UIColor blueColor];
    mainScrollView.scrollEnabled = YES;
    mainScrollView.delegate = self;

    mainView.frame = CGRectMake((screenWidth/2) - 25.0f, (screenHeight/2) - 25.0f, 50.0f, 50.0f);

    UIImageView *testImageView = [[UIImageView alloc] init];
    testImageView.backgroundColor = [UIColor redColor];
    testImageView.frame = CGRectMake(0.0f, 0.0f, 50.0f, 50.0f);

    // Add subviews

    [self.view addSubview:mainScrollView];
    [mainScrollView addSubview:mainView];
    [mainView addSubview:testImageView];

}

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
    return mainView;
}

The zoom works well now. However, I can only pan when the UIScrollView is at the minimum zoom. All other times, when I pinch-zoom in, when I release my fingers the UIView shifts slightly off-centre, despite being centred when I was zooming, and I can no longer pan the UIScrollView.

Also, after zooming in, if I zoom back out again to minimum zoom, I still cannot pan.

TL;DR - In other words, UIScrollView's pan only before using the pinch zoom feature, after which it breaks.

How can I prevent this from happening, and allow the UIScrollView's pan to always be enabled? All help appreciated.

Answer 1

Try to add another view in scrollView with same size of screen and then add mainView and imageView. It may solve your proble. :)