UIScrollView 实现比例缩放

 #import "RootViewController.h"
 
 @interface RootViewController ()<UIScrollViewDelegate>
 {
     UIImageView *imageView;
     UILabel *scaleRatioLabel;// 显示倍率用的Label
 }
 @property (nonatomic, strong)UIScrollView *scrollView;
 
 @end
 
 @implementation RootViewController
 
 - (void)dealloc
 {
     self.scrollView = nil;
 }
 
 - (void)viewDidLoad {
     [super viewDidLoad];
     self.scrollView = [[UIScrollView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
     self.scrollView.delegate = self;
     [self.view addSubview:self.scrollView];
     imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"1-3.jpg"]];
     [imageView setCenter:CGPointMake([UIScreen mainScreen].bounds.size.width/2.0, [UIScreen mainScreen].bounds.size.height/2.0)];
     [self.scrollView addSubview:imageView];
     //内容大小与图片大小一致
     self.scrollView.contentSize = imageView.frame.size;
     // 最小缩放比例
     self.scrollView.minimumZoomScale = 0.2f;
     // 最大缩放比例
     self.scrollView.maximumZoomScale = 5.0f;
 
     // 用来显示倍率的Label
     scaleRatioLabel = [[UILabel alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width/2.0 - , [UIScreen mainScreen].bounds.size.height/2.0 - 12.5, , )];
     [scaleRatioLabel setBackgroundColor:[UIColor clearColor]];
     [self.view addSubview:scaleRatioLabel];
 
 }
 
 #pragma mark - UIScrollViewDelegate
 // 设置要缩放的控件
 - (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
 {
     return imageView;
 }
 
 // 处理结束缩放事件
 - (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(CGFloat)scale
 {
     [self.view bringSubviewToFront:scaleRatioLabel];
     [scaleRatioLabel setAlpha:0.6f];
     [scaleRatioLabel setBackgroundColor:[UIColor lightGrayColor]];
     scaleRatioLabel.text = [NSString stringWithFormat:@" x%.1f",scale];
 
     [UIView transitionWithView:scaleRatioLabel duration:2.0f options:UIViewAnimationOptionCurveEaseInOut animations:^{
         scaleRatioLabel.alpha = 0.0f;
     } completion:nil];
 }
 
 @end