iOS 7 Auto Layout - UIImageView inside UIScrollView - uiscrollview

Question

I have a simple view in an iOS application which is causing me some problems.
In this view I have a UIScrollView (full width/height of main view), which is pinned to the top/bottom/leading/trailing of the main view (in IB).
Inside the UIScrollView I have a UIImageView which is pinned top/bottom/leading/trailing to the UIScrollView.
Now, the image inside the UIImageView is almost double the size of the main view, therefore the content mode of the UIImageView is set to Aspect Fit. My problem is that when I run the project, the image is being displayed at its actual size.
The reason the UIImageView is inside the UIScrollView is due to the fact that I want the user to be able to zoom in to the image (hence the reason it is double the size).
I also want the user to be able to rotate the screen as the image may be in portrait or landscape format depending on which image they choose to view in the previous view.
Surely this should be easy enough to do (in IB as well), however I cannot for the life of me figure it out.

Answer 1

You also have to add width and height constraints for UIImageView. It is caused by the fact that by default UIImageView has an intrinsic content size derived from the size of the image.
Following is code snippet for defining those constraints:
[scrollView addConstraint:[NSLayoutConstraint constraintWithItem:imageView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:scrollView attribute:NSLayoutAttributeWidth multiplier:1.0f constant:0]];
[scrollView addConstraint:[NSLayoutConstraint constraintWithItem:imageView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:scrollView attribute:NSLayoutAttributeHeight multiplier:1.0f constant:0]];
Even you can do this in IB.

Answer 2

If I understand your question, you want the content to be zoomed out at the start. Assuming that your content does not have the same aspect ratio as the phone (a safe assumption), you can either "letter box" / "curtain" the content, or only zoom out until either the height or width of the image would show on the phone (before aforementioned letter boxing). I chose this latter approach, and set my min zoom to be the greater of min zooms for either dimension.
The code is thus:
// configure image and scroll view for scrolling to extents of actual image
double widthScale = self.view.frame.size.width / image.size.width;
double heightScale = self.view.frame.size.height / image.size.height;
self.scrollView.minimumZoomScale = MAX(widthScale, heightScale);
self.scrollView.maximumZoomScale = MIN(1 / widthScale, 1 / heightScale) / [[UIScreen mainScreen] scale]; // scale to pixel resolution
self.scrollView.zoomScale = self.scrollView.minimumZoomScale;
It assumes that you are using full screen.
If you want the min of either dimension, use this:
self.scrollView.minimumZoomScale = MIN(widthScale, heightScale);