UIScrollView实现图片缩放（二）

UIScrollView已经定义了捏合和移动的手势，正常的操作来说，还会使用双击图片进行缩放，这需要我们自己收动在UIScrollView加上点击的手势

1.添加手势

        let doubleTapGesture = UITapGestureRecognizer(target: self,action: #selector(FLCameraFilterTopView.handleDoubleTap(_:)))
       doubleTapGesture.numberOfTapsRequired = 2
       scrollView.addGestureRecognizer(doubleTapGesture)

2.处理点击手势

    func handleDoubleTap(tap:UITapGestureRecognizer) {
        
        //获取当前缩放值
        var newScale = scrollView.zoomScale
        
        if scrollView.zoomScale == 1 {
            newScale = 0.8
        }else {
            newScale = 1
        }
        
        //获取要缩放的大小和起始位置，这里都是居中
        let zoomRect = self.zoomRectForScale(newScale, center: CGPointMake(FL.ScreenWidth/2,FL.ScreenWidth/2))

        scrollView.zoomToRect(zoomRect, animated: true)
    }
    
    func zoomRectForScale(scale:CGFloat,center:CGPoint) -> CGRect {
        
        var zoomRect = CGRectZero
        
        zoomRect.size.height = scrollView.frame.size.height / scale
        zoomRect.size.width = scrollView.frame.size.width / scale
        zoomRect.origin.x = center.x - zoomRect.size.width/2.0
        zoomRect.origin.y = center.y - zoomRect.size.height/2.0
        
        return zoomRect
    }
```
3. UIScrollViewDelegate 里设置

```
    func scrollViewDidEndZooming(scrollView: UIScrollView, withView view: UIView?, atScale scale: CGFloat) {
        //保证下一次的缩放在前次缩放的基础上
        scrollView.setZoomScale(scale, animated: true)
    }
    
```