UIImage in scrollview too big - ios

Question

I am trying to show a UIImage inside a scrollview. The image is much larger in size than the scrollview, so it displays only the top-left corner of the image. I can then zoom / rearrange the image to fit a little better, but i want it to display the WHOLE image, centered and fitting inside. The user can then zoom around if he wants to, but the default should show entire image.
Here is my code (it downloads the image):
UIImage *trackImg = [UIImage imageWithContentsOfFile:trackImagePath];
/* Scrollview! */
imgView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
[imgView setImage:trackImg];
[[self scrImageViewer] addSubview:imgView];
_scrImageViewer.delegate = self;
_scrImageViewer.contentSize = trackImg.size;
_scrImageViewer.contentOffset = CGPointMake(trackImg.size.width/2, trackImg.size.height/2);
_scrImageViewer.minimumZoomScale = 1;
_scrImageViewer.maximumZoomScale = 4;
_scrImageViewer.zoomScale = 2;
_scrImageViewer.clipsToBounds = YES;
CGFloat newContentOffsetX = (_scrImageViewer.contentSize.width - _scrImageViewer.frame.size.width) / 2;
CGFloat newContentOffsety = (_scrImageViewer.contentSize.height - _scrImageViewer.frame.size.height) / 2;
_scrImageViewer.contentOffset = CGPointMake(newContentOffsetX, newContentOffsety);
Again, it shows only the top-left corner of image. I want it to display the whole image.
Thanks :)

Answer 1

In this image you can see a small scrollView (that square is the size of the scrollview) with a really big image inside (height is 1280 and the scroll view is only 100). The only thing you need to do is to add the constraints of your image to its superview (scrollView), in my case I added all 0 (top, leading, trailing and bottom) and the imageView mode is Center. Of course you need to add constraints from your scrollview to its superView, in this case the View.
If you need to add the imageView also programatically, if you can't use an outlet, you can make these changes on your code, but I would strongly recommend you use the storyboard solution:
imgView = [[UIImageView alloc] initWithImage:trackImg];
[self.scrImageViewer addSubview:imgView];
[imgView setTranslatesAutoresizingMaskIntoConstraints:NO];
[self.scrImageViewer addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"V:|[view]|" options:0 metrics:nil views:#{ #"view": imgView }]];
[self.scrImageViewer addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:|[view]|" options:0 metrics:nil views:#{ #"view": imgView }]];
[self.view layoutIfNeeded];