UIScrollView with an ImageView not scrolling vertically

Question

I have a UIImageView and it has an image larger than the screen size. I have this UIImageView as a sub view of UIScrollView. Now, I am unable to scroll down. to view the whole image. But the zooming functionalities are working fine.

@IBOutlet weak var scrollView: UIScrollView!

var imageView = UIImageView();

override func viewDidLoad() {
    super.viewDidLoad()
}

func centerScrollViewContents(){
    let boundsSize = scrollView.bounds.size
    var contentsFrame = imageView.frame

    if contentsFrame.size.width < boundsSize.width {
       contentsFrame.origin.x = (boundsSize.width - contentsFrame.size.width) / 2
    }
    else { 
       contentsFrame.origin.x = 0
    }

    if contentsFrame.size.height < boundsSize.height {            
        contentsFrame.origin.y = (boundsSize.height - contentsFrame.size.height) / 2
    }
    else {
        contentsFrame.origin.y = 0
    }

    imageView.frame = contentsFrame
   // scrollView.frame = contentsFrame        
}

func scrollViewDidZoom(scrollView: UIScrollView) {
    centerScrollViewContents()
}

func viewForZoomingInScrollView(scrollView: UIScrollView) -> UIView? {
    return imageView
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()

    // Dispose of any resources that can be recreated.
}

override func viewDidAppear(animated: Bool) {

    scrollView.delegate = self
    imageView.frame = CGRectMake(0, 0, scrollView.frame.size.width, scrollView.frame.size.height)

   // imageView.contentMode = UIViewContentMode.ScaleAspectFill
   // imageView.clipsToBounds = true
    imageView.image = UIImage(named: imgstr)

    var imagee = UIImage(named: imgstr)
    let size = imagee?.size
   // imageView.frame = CGRectMake(0, 0, size.width!, size.height!)
    imageView.contentMode = .Top
    scrollView.addSubview(imageView)

    scrollView.contentSize = size!
    let scrollViewFrame = scrollView.frame
    let scaleWidth = scrollViewFrame.size.width / scrollView.contentSize.width
    let scaleHeight = scrollViewFrame.size.height / scrollView.contentSize.height
    let minScale = min(scaleHeight, scaleWidth)

    scrollView.minimumZoomScale = 1
    scrollView.maximumZoomScale = 5
    scrollView.zoomScale = minScale

    centerScrollViewContents()   
}

Answer 1

You have to solve two main problems to your UIScrollView work

1. One problem reside inside where you initialize all the data for the UIScrollView, I mean the function viewDidAppear.
2. You must set the constraints for you UIScrollView like Top, Bottom, Left and Right to 0 respect the your SuperView.

If you put the code inside your viewDidAppear inside of your function viewDidLoad and delete your function viewDidAppear, it works fine as you want. Like in the following way:

override func viewDidLoad() {
    super.viewDidLoad()


    scrollView.delegate = self
    imageView.frame = CGRectMake(0, 0, scrollView.frame.size.width, scrollView.frame.size.height)

    // imageView.contentMode = UIViewContentMode.ScaleAspectFill
    // imageView.clipsToBounds = true
    imageView.image = UIImage(named: "imgstr.jpg")

    var imagee = UIImage(named: "imgstr.jpg")
    let size = imagee?.size
    // imageView.frame = CGRectMake(0, 0, size.width!, size.height!)
    imageView.contentMode = .Top
    scrollView.addSubview(imageView)

    scrollView.contentSize = size!
    let scrollViewFrame = scrollView.frame
    let scaleWidth = scrollViewFrame.size.width / scrollView.contentSize.width
    let scaleHeight = scrollViewFrame.size.height / scrollView.contentSize.height
    let minScale = min(scaleHeight, scaleWidth)

    scrollView.minimumZoomScale = 1
    scrollView.maximumZoomScale = 5
    scrollView.zoomScale = minScale

    centerScrollViewContents()
}

You must too set the constraints for the UIScrollView in your Storyboard

I though that the problem reside in the following difference:

• viewDidAppear is called when the view is actually visible, and can be called multiple times during the lifecycle of a View Controller (for instance, when a Modal View Controller is dismissed and the view becomes visible again). This is where you want to perform any layout actions or do any drawing in the UI - for example, presenting a modal view controller. However, anything you do here should be repeatable. It's best not to retain things here, or else you'll get memory leaks if you don't release them when the view disappears.
• viewDidLoad is called exactly once, when the view controller is first loaded into memory. This is where you want to instantiate any instance variables and build any views that live for the entire lifecycle of this view controller. However, the view is usually not yet visible at this point.

If you any problem I have a project ready to submit to Github if you want to see it.

UPDATE: After test it again your code, I resume your error to less code. Your code work fine, if you put your line imageView.frame = CGRectMake(0, 0, size!.width, size!.height) your code works fine without contraints.

Something like this :

override func viewDidAppear(animated: Bool) {


    scrollView.delegate = self        

    // imageView.contentMode = UIViewContentMode.ScaleAspectFill
    // imageView.clipsToBounds = true
    imageView.image = UIImage(named: "imgstr.jpg")

    var imagee = UIImage(named: "imgstr.jpg")
    let size = imagee?.size

    // This line should be here!!!
    imageView.frame = CGRectMake(0, 0, size!.width, size!.height)
    imageView.contentMode = .Top
    scrollView.addSubview(imageView)

    scrollView.contentSize = size!
    let scrollViewFrame = scrollView.frame
    let scaleWidth = scrollViewFrame.size.width / scrollView.contentSize.width
    let scaleHeight = scrollViewFrame.size.height / scrollView.contentSize.height
    let minScale = min(scaleHeight, scaleWidth)

    scrollView.minimumZoomScale = 1
    scrollView.maximumZoomScale = 5
    scrollView.zoomScale = minScale

    centerScrollViewContents()       

}

The key is that in your previous code you set the frame for the image as the frame of the scrollView not at the size of the image that is bigger than the scrollView.

I hope this help you.