模拟系统照相机图片裁剪的功能

//
//  RootViewController.m
//  ScrollView
//
//  Copyright (c) 2014年 Y.X. All rights reserved.
//

#import "RootViewController.h"

@interface RootViewController ()<UIScrollViewDelegate>

{
    BOOL tapped;
}

@property (nonatomic, strong) UIScrollView           *scrollView;
@property (nonatomic, strong) UIImageView            *imageView;
@property (strong, nonatomic) UITapGestureRecognizer *tapGesture;

@end

@implementation RootViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor blackColor];
    
    // scrollView
    {
        _scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, 200, 200)];
        [self.view addSubview:_scrollView];
        
        _scrollView.center              = self.view.center;
        _scrollView.delegate            = self;
        _scrollView.layer.borderWidth   = 2.f;
        _scrollView.layer.borderColor   = [UIColor redColor].CGColor;
        _scrollView.layer.masksToBounds = NO;
        
        // 不显示滚动的条
        _scrollView.showsHorizontalScrollIndicator = NO;
        _scrollView.showsVerticalScrollIndicator   = NO;

        _scrollView.bouncesZoom      = YES;
        _scrollView.minimumZoomScale = 1.f;
        _scrollView.maximumZoomScale = 10.f;
        _scrollView.contentMode      = UIViewContentModeScaleAspectFit;
    }
    
    // 图片
    _imageView       = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 200, 200)];
    _imageView.image = [UIImage imageNamed:@"back"];
    _imageView.contentMode = UIViewContentModeScaleAspectFit;
    [_scrollView addSubview:_imageView];
    
    // 手势
    _tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self
                                                          action:@selector(tapRecognized:)];
    [_scrollView addGestureRecognizer:_tapGesture];
}

- (void)tapRecognized:(id)sender
{
    if (!tapped)
    {
        CGPoint tapPoint = [self.tapGesture locationOfTouch:0
                                                     inView:self.tapGesture.view];
        CGRect zoomRect = [self zoomRectForScrollView:self.scrollView
                                            withScale:6.0f
                                           withCenter:tapPoint];
        [self.scrollView zoomToRect:zoomRect animated:YES];
        tapped = YES;
    }
    else
    {
        [self.scrollView setZoomScale:1.0f animated:YES];
        tapped = NO;
    }
}


- (CGRect)zoomRectForScrollView:(UIScrollView *)scrollView
                      withScale:(float)scale
                     withCenter:(CGPoint)center
{
    CGRect zoomRect;
    zoomRect.size.height = scrollView.frame.size.height / scale;
    zoomRect.size.width  = scrollView.frame.size.width / scale;
    zoomRect.origin.x    = center.x - (zoomRect.size.width / 2.0);
    zoomRect.origin.y    = center.y - (zoomRect.size.height / 2.0);
    return zoomRect;
}

#pragma mark - UIScrollView代理方法
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
    return self.imageView;
}

@end