@property (nonatomic, strong) UIImageView *smallImageView;// 小图视图
@property (nonatomic, strong) UIImageView *bigImageView;// 大图视图
@property (nonatomic, strong) UIView *bgView;// 阴影视图

- (void)viewDidLoad {
 [super viewDidLoad];

 // 小图
 self.smallImageView = [[UIImageView alloc] initWithFrame:CGRectMake((SCREENWIDTH - 100)/2, (SCREENHEIGHT - 100)/2, 100, 100)];
 self.smallImageView.image = [UIImage imageNamed:@"icon"];
 // 添加点击响应
 self.smallImageView.userInteractionEnabled = YES;
 UITapGestureRecognizer *imageTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(viewBigImage)];
 [self.smallImageView addGestureRecognizer:imageTap];
 [self.view addSubview:self.smallImageView];
}

// 大图视图
- (UIImageView *)bigImageView {
 if (nil == _bigImageView) {
 _bigImageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, (SCREENHEIGHT - SCREENWIDTH) / 2, SCREENWIDTH, SCREENWIDTH)];
 [_bigImageView setImage:self.smallImageView.image];
 // 设置大图的点击响应，此处为收起大图
 _bigImageView.userInteractionEnabled = YES;
 UITapGestureRecognizer *imageTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(dismissBigImage)];
 [_bigImageView addGestureRecognizer:imageTap];
 }
 return _bigImageView;
}

// 阴影视图
- (UIView *)bgView {
 if (nil == _bgView) {
 _bgView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, SCREENWIDTH, SCREENHEIGHT)];
 _bgView.backgroundColor = [UIColor colorWithWhite:0 alpha:0.5];
 // 设置阴影背景的点击响应，此处为收起大图
 _bgView.userInteractionEnabled = YES;
 UITapGestureRecognizer *bgTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(dismissBigImage)];
 [_bgView addGestureRecognizer:bgTap];
 }
 return _bgView;
}

// 显示大图
- (void)viewBigImage {
 [self bigImageView];// 初始化大图

 // 让大图从小图的位置和大小开始出现
 CGRect originFram = _bigImageView.frame;
 _bigImageView.frame = self.smallImageView.frame;
 [self.view addSubview:_bigImageView];

 // 动画到大图该有的大小
 [UIView animateWithDuration:0.3 animations:^{
 // 改变大小
 _bigImageView.frame = originFram;
 // 改变位置
 _bigImageView.center = self.view.center;// 设置中心位置到新的位置
 }];

 // 添加阴影视图
 [self bgView];
 [self.view addSubview:_bgView];

 // 将大图放到最上层，否则会被后添加的阴影盖住
 [self.view bringSubviewToFront:_bigImageView];
}

// 收起大图
- (void)dismissBigImage {
 [self.bgView removeFromSuperview];// 移除阴影

 // 将大图动画回小图的位置和大小
 [UIView animateWithDuration:0.3 animations:^{
 // 改变大小
 _bigImageView.frame = self.smallImageView.frame;
 // 改变位置
 _bigImageView.center = self.smallImageView.center;// 设置中心位置到新的位置
 }];

 // 延迟执行，移动回后再消灭掉
 double delayInSeconds = 0.3;
 __block ViewController* bself = self;
 dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
 dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
 [bself.bigImageView removeFromSuperview];
 bself.bigImageView = nil;
 bself.bgView = nil;
 });
}