最终效果

• Platform: iOS8.0+
• Language: Swift3.0
• Editor: Xcode8

1.在storyboard上拖一个UIScrollView

scrollview 约束

2.再在UIScrollView中拖一个UIImageView

01 imageview 约束

02 为了避免约束报错/警告，给imageview设置一张图片

03 Update Frames

3.绑定@IBOutlet

    @IBOutlet weak var scrollView: UIScrollView!
    @IBOutlet weak var imageView: UIImageView!
    
// 约束 - 居中显示用
    @IBOutlet weak var ivLeadingCons: NSLayoutConstraint!
    @IBOutlet weak var ivTrailingCons: NSLayoutConstraint!
    @IBOutlet weak var ivTopCons: NSLayoutConstraint!
    @IBOutlet weak var ivBottomCons: NSLayoutConstraint!

4.添加方法

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()

        scaleImageViewForAdjustingViewSize()
    }
    
    // 缩放到屏幕合适
    fileprivate func scaleImageViewForAdjustingViewSize()
    {
        let minScale = min(view.bounds.size.width / imageView.bounds.size.width, view.bounds.size.height / imageView.bounds.size.height)
        
        scrollView.minimumZoomScale = minScale //最小缩放值
        scrollView.zoomScale = minScale //当前缩放值
    }
    
    // 居中显示
    fileprivate func updateConstraintsForPositioningImageViewCenterly()
    {
       let yOffset = max(0, (view.bounds.size.height - imageView.frame.size.height)/2)
        
        let xOffset = max(0, (view.bounds.size.width - imageView.frame.size.width)/2)
        
        // 设置约束 - 相当于设置scrollview的contentsize，这样它才能滚动内容
        ivTopCons.constant = yOffset
        ivBottomCons.constant = yOffset
        ivLeadingCons.constant = xOffset
        ivTrailingCons.constant = xOffset
        
        view.layoutIfNeeded()
    }

extension ViewController: UIScrollViewDelegate{
    func viewForZooming(in scrollView: UIScrollView) -> UIView? {
        return imageView
    }
    
    func scrollViewDidZoom(_ scrollView: UIScrollView) {
        updateConstraintsForPositioningImageViewCenterly()
    }
}

5.Build and run to see what does it looks like.

如果对你有帮助，别忘了点个❤️哦。