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scrollview当前显示区域顶点相对于frame顶点的偏移量.
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.是scrollview的contentview的顶点相对于scrollview的位置.
_|←_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) / :
let verticalSpace = imageSize.height < scrollViewSize.height ? (scrollViewSize.height - imageSize.height) / :
scrollView.contentInset = UIEdgeInsets(top: verticalSpace,
left: horizontalSpace,
bottom: verticalSpace,
right: horizontalSpace)
}
ScrollView中键盘的高度适应，实现代码
NSNotificationCenter.defaultCenter().addObserver(self, selector: "keyboardWillShow:", name: UIKeyboardWillShowNotification, object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: "keyboardWillHide:", name: UIKeyboardWillHideNotification, object: nil)
func keyboardWillShow(notification:NSNotification) {
adjustInsetForKeyboard(true, notification: notification)
}
func keyboardWillHide(notification:NSNotification) {
adjustInsetForKeyboard(false, notification: notification)
}
func adjustInsetForKeyboard(show:Bool, notification:NSNotification) {
let userInfo = notification.userInfo ?? [:]
let keyboardFrame = (userInfo[UIKeyboardFrameBeginUserInfoKey] as! NSValue).CGRectValue()
let adjustHeight = (keyboardFrame.height + ) * (show ? : -)
scrollView1.contentInset.bottom += adjustHeight
scrollView1.scrollIndicatorInsets.bottom += adjustHeight
}