iOS 6 Autolayout - ScrollView with embedded ImageView not zooming properly

2
votes

I am trying to setup a simple view that displays an image and allows users to zoom in/out and pan the image as they desire. I have autoLayout enabled and the view consists of a UIScrollView with an embedded UIImageView. Both views are sized to the entire screen.

I used the logic and code from Apple's ScrollViewSuite (the "1_TapToZoom" sample) and everything seems correct. However, when pinching the view, the ScrollView/ImageView gets all distorted and doesn't respond properly. Hard to explain the behavior, but lets just call it "funky". The size and aspect changes in no consistent manner.

My GUESS is that this has to do with autolayout constraints. Does anyone have some suggestions/fixes for this?

1
iosuiscrollviewuiimageviewautolayoutzooming

1 Answers

0
votes

The issues that occurs is the changing of location of the imageview during the zoom process. The origin location of the imageview will change to be a negative value during the zoom. I believe this is why the jerky movement occurs. As well, after the zoom is complete the imageView is still in the wrong location meaning that scrolls will appear to be offset.

If you implement -(void) scrollViewDidZoom:(UIScrollView *)scrollView and log the frame of the UIImageView during this time you can see its origin changing.

I ended up making things work out by implementing a strategy like this: https://github.com/mattneub/Programming-iOS-Book-Examples/blob/master/ch20p573scrollViewAutoLayout/ch20p573scrollViewAutoLayout/ViewController.m

And in addition changing the frame of the contentView while zooming

-(void) scrollViewDidZoom:(UIScrollView *)scrollView {
    CGRect cFrame = self.contentView.frame;
    cFrame.origin = CGPointZero;
    self.contentView.frame = cFrame;
}