iOS笔记之ScrollView

ScrollView三个基本的要理解的属性;

contentSize

The size of the content view.所以很好理解,contentSize也就是scrollView可滚动的区域.

contentOffset

The point at which the origin of the content view is offset from the origin of the scroll view.

这里标注的是point,是当前显示的区域的origin相对于整个scrollView的origin的位置.

contentInset

The distance that the content view is inset from the enclosing scroll view.

这里说得是distance,四个值分别是上下左右, 默认值是 UIEdgeInsetsZero,也就是四个值都为0.

  _|←_cW_→_|_↓_
   |       | 
---------------
   |content| ↑
 ↑ |content| contentInset.top
cH |content||content| contentInset.bottom
   |content|---------------
  _|_______|___ 
             ↑

(cH = contentSize.height; cW = contentSize.width)

  

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView; //返回要缩放的图片(必须在代理类里实现)

 

图片缩放保持居中,实现代码:

(在viewWillLayoutSubviews也要调用)

    func recenterImage() {
        let scrollViewSize = scrollView.bounds.size
        let imageSize = imageView.frame.size
        
        let horizontalSpace = imageSize.width < scrollViewSize.width ? (scrollViewSize.width - imageSize.width) / 2 : 0
        let verticalSpace = imageSize.height < scrollViewSize.height ? (scrollViewSize.height - imageSize.height) / 2 : 0
        
        scrollView.contentInset = UIEdgeInsets(top: verticalSpace,
            left: horizontalSpace,
            bottom: verticalSpace,
            right: horizontalSpace)
    }

 

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