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 - 25, [UIScreen mainScreen].bounds.size.height/2.0 - 12.5, 50, 25)];
    [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