An ImageViewer

ImageViewerViewController.swift

//
//   ImageViewerViewController.swift
//  GJHP2P
//
//  Created by race on 15/11/30.
//  Copyright © 2015年 Guijinhui. All rights reserved.
//

import UIKit

class  ImageViewerViewController: UIViewController, UIScrollViewDelegate {

  let scrollView = UIScrollView()
  let imageView = UIImageView()
  var image: UIImage?

  // MARK: Life-Cycle

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

  func setupView() {
    view.backgroundColor = UIColor.blackColor()
    scrollView.frame = view.bounds
    scrollView.delegate = self
    scrollView.minimumZoomScale = 1.0
    scrollView.maximumZoomScale = 3.0
    scrollView.zoomScale = 1.0
    view.addSubview(scrollView)

    if let image = image {
      imageView.contentMode = .ScaleAspectFill
      imageView.frame = centerFrameFromImage(image)
      imageView.image = image
    }
    scrollView.addSubview(imageView)

    let doubleTapRecognizer = UITapGestureRecognizer(target: self, action: "handleDoubleTap:")
    doubleTapRecognizer.numberOfTapsRequired = 2
    doubleTapRecognizer.numberOfTouchesRequired = 1
    scrollView.addGestureRecognizer(doubleTapRecognizer)
  }

  // MARK: Gesture Recognizers

  func handleDoubleTap(recognizer: UITapGestureRecognizer!) {
    let pointInView = recognizer.locationInView(self.imageView)
    self.zoomInZoomOut(pointInView)
  }

  // MARK: ScrollView

  func centerFrameFromImage(image: UIImage?) -> CGRect {
    if image == nil {
      return CGRectZero
    }

    let scaleFactor = scrollView.frame.size.width / image!.size.width
    let newHeight = image!.size.height * scaleFactor

    var newImageSize = CGSize(width: scrollView.frame.size.width, height: newHeight)

    newImageSize.height = min(scrollView.frame.size.height, newImageSize.height)

    let centerFrame = CGRect(x: 0.0, y: scrollView.frame.size.height/2 - newImageSize.height/2, width: newImageSize.width, height: newImageSize.height)

    return centerFrame
  }

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

  func centerScrollViewContents() {
    let boundsSize = scrollView.frame
    var contentsFrame = self.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 - scrollView.scrollIndicatorInsets.top - scrollView.scrollIndicatorInsets.bottom - contentsFrame.size.height) / 2.0
    } else {
      contentsFrame.origin.y = 0.0
    }

    self.imageView.frame = contentsFrame
  }

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

  func zoomInZoomOut(point: CGPoint!) {
    let newZoomScale = self.scrollView.zoomScale > (self.scrollView.maximumZoomScale/2) ? self.scrollView.minimumZoomScale : self.scrollView.maximumZoomScale

    let scrollViewSize = self.scrollView.bounds.size

    let width = scrollViewSize.width / newZoomScale
    let height = scrollViewSize.height / newZoomScale
    let x = point.x - (width / 2.0)
    let y = point.y - (height / 2.0)

    let rectToZoom = CGRect(x: x, y: y, width: width, height: height)
    self.scrollView.zoomToRect(rectToZoom, animated: true)
  }
}