使用scrollview实现图片放大缩小

#import "ViewController.h"
#import <UIKit/UIMenuController.h>

@interface ViewController ()<UIScrollViewDelegate>
@property (strong, nonatomic) UIScrollView *scrView;

@property (nonatomic,strong)UIImageView *imgv;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    //[[UILabel appearance] setTextColor:[UIColor yellowColor]];
    self.scrView = [[UIScrollView alloc]initWithFrame:self.view.bounds];
    self.scrView.contentSize = CGSizeMake(800, 1800);
    self.scrView.backgroundColor =  [UIColor yellowColor];
    [self.view addSubview:self.scrView];


    // 设置放大缩小的比例
    self.scrView.multipleTouchEnabled = YES;//打开多指触控
    self.scrView.maximumZoomScale = 2.0;
    self.scrView.minimumZoomScale = 0.5;
    self.scrView.zoomScale = 3.0;

    self.scrView.delegate = self;

    UIImageView *imgv = [[UIImageView alloc]initWithFrame:CGRectMake(150, 150, 150, 150)];
    imgv.backgroundColor = [UIColor grayColor];
    [self.scrView addSubview:imgv];
    self.imgv = imgv;

}

// *** 必须实现的代理方法

-(UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView{
    return self.imgv;
}
// ***是图片保持位于视图中心

-(void)scrollViewDidZoom:(UIScrollView *)scrollView{
    self.imgv.center = self.view.center;
}