readme.md

##Simple Storyboard/Autolayout Full-Screen Image Viewer

Supports

• Double-tap to zoom/unzoom
• Panning
• Pinch-zooming

Inspired by: http://www.raywenderlich.com/76436/use-uiscrollview-scroll-zoom-content-swift

Note: This example assumes you're using MBProgressHUD for displaying loading indicators, and SDWebImage for loading web-based images asynchronously.

###Instructions

1. Create a new view controller via storyboard.
2. Add a UIScollView to the view controller, and constraint it as desired.
3. Using control-drag, set the UIScrollView's reference outlet to the @IBOutlet weak var scrollView: UIScrollView! property and the delegate to the ImageViewController class.

ImageViewController.swift

import UIKit
import MBProgressHUD

class ImageViewController: UIViewController, UIScrollViewDelegate {
    
    @IBOutlet weak var scrollView: UIScrollView!
    
    var imageURL: String?
    private var imageView: UIImageView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        MBProgressHUD.showHUDAddedTo(self.view, animated: true)
        imageView = UIImageView()
        imageView.sd_setImageWithURL(NSURL(string: imageURL!), completed: { [weak self] (image, error, cacheType, url) -> Void in
            self?.configureSizeAndZoomScale(image)
            MBProgressHUD.hideHUDForView(self?.view, animated: true)
        })
    }
    
    override func viewWillTransitionToSize(size: CGSize, withTransitionCoordinator coordinator: UIViewControllerTransitionCoordinator) {
        super.viewWillTransitionToSize(size, withTransitionCoordinator: coordinator)
        coordinator.animateAlongsideTransition({ context in self.centerScrollViewContents() }, completion: nil)
    }
    
    @IBAction func scrollViewDoubleTapped(recognizer: UITapGestureRecognizer) {
        let pointInView = recognizer.locationInView(imageView)
        if scrollView.zoomScale < scrollView.maximumZoomScale {
            zoomToScale(scrollView.maximumZoomScale, pointInView: pointInView)
        } else {
            zoomToScale(scrollView.minimumZoomScale, pointInView: pointInView)
        }
    }
    
    func configureSizeAndZoomScale(image: UIImage?) {
        if let image = image {
            imageView.frame = CGRect(origin: CGPoint(x: 0, y: 0), size:image.size)
            scrollView.addSubview(imageView)
            scrollView.contentSize = image.size
            
            let scrollViewFrame = scrollView.frame
            let scaleWidth = scrollViewFrame.size.width / scrollView.contentSize.width
            let scaleHeight = scrollViewFrame.size.height / scrollView.contentSize.height
            let minScale = min(scaleWidth, scaleHeight)
            
            scrollView.minimumZoomScale = minScale
            scrollView.maximumZoomScale = 1.0
            scrollView.zoomScale = minScale
            
            centerScrollViewContents()
        }
    }
    
    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) / 2.0
        } else {
            contentsFrame.origin.x = 0.0
        }
        
        if contentsFrame.size.height < boundsSize.height {
            contentsFrame.origin.y = (boundsSize.height - contentsFrame.size.height) / 2.0
        } else {
            contentsFrame.origin.y = 0.0
        }
        
        imageView.frame = contentsFrame
    }
    
    func zoomToScale(scale: CGFloat, pointInView: CGPoint) {
        let scrollViewSize = scrollView.bounds.size
        let w = scrollViewSize.width / scale
        let h = scrollViewSize.height / scale
        let x = pointInView.x - (w / 2.0)
        let y = pointInView.y - (h / 2.0)
        
        let rectToZoomTo = CGRectMake(x, y, w, h);
        
        scrollView.zoomToRect(rectToZoomTo, animated: true)
    }

    
    //MARK: - UIScrollViewDelegate
    func viewForZoomingInScrollView(scrollView: UIScrollView) -> UIView? {
        return imageView
    }
    
    func scrollViewDidZoom(scrollView: UIScrollView) {
        centerScrollViewContents()
    }
}