UIScrollView實現縮放非常簡單。
1、首先新增代理UIScrollViewDelegate，並且設定自己建立的UIScrollView物件的代理scrollView.delegate = self;;

2、定義縮放的最大比例和最小比例;
比如：

#define minScale  1
#define maxScale  2


[_scrollView setMinimumZoomScale:minScale];
[_scrollView setMaximumZoomScale:maxScale];
[_scrollView setZoomScale:minScale animated:YES];
 

3、實現代理方法

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
    return scrollVew中要縮放的檢視;   
}


// called before the scroll view begins zooming its content縮放開始的時候呼叫
- (void)scrollViewWillBeginZooming:(UIScrollView *)scrollView withView:(nullable UIView *)view NS_AVAILABLE_IOS(3_2){
    NSLog
 
(@"%s",__func__);
}

// scale between minimum and maximum. called after any 'bounce' animations縮放完畢的時候呼叫。
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(CGFloat)scale

{
    //把當前的縮放比例設進ZoomScale，以便下次縮放時實在現有的比例的基礎上
    NSLog(@"scale is %f",scale);
    [_scrollView setZoomScale:scale animated:NO
 
];
}

// 縮放時呼叫
- (void)scrollViewDidZoom:(UIScrollView *)scrollView{
    // 可以實時監測縮放比例
    NSLog(@"......scale is %f",scrollView.zoomScale);

}