图片的缩放功能实现

1.如果是单张图片的缩放，那么首先创建一个UIScrollView，注意设置代理和缩放系数

- (UIScrollView *)scrollView {
    if (!_scrollView) {
        _scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, [UIApplication sharedApplication].statusBarFrame.size.height, self.frame.size.width, self.frame.size.height - [UIApplication sharedApplication].statusBarFrame.size.height)];

        _scrollView.maximumZoomScale = 3.0;
        _scrollView.minimumZoomScale = 0.5;
        _scrollView.delegate = self;
    }
    return _scrollView;
}

2.创建需要缩放的imageView

- (UIImageView *)imageView {
    if (!_imageView) {
        _imageView = [[UIImageView alloc] init];

    }
    return _imageView;
}

3.将scrollView添加到view中，imageView添加到scrollView中,注意scrollView要设置代理，并实现下面几个方法

//返回需要放大的view，必须实现
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView {
    return _imageView;
}

- (void)scrollViewWillBeginZooming:(UIScrollView *)scrollView withView:(UIView *)view {
    NSLog(@"willZoom");
}

//让图片缩放后可以居中
- (void)scrollViewDidZoom:(UIScrollView *)scrollView {
    NSLog(@"didZoom");
    //没有放大的情况下，偏移量为(scrollView.bounds.size.width - scrollView.contentSize.width)/2
    CGFloat offsetX = (scrollView.bounds.size.width > scrollView.contentSize.width)?(scrollView.bounds.size.width - scrollView.contentSize.width)/2 : 0.0;

    CGFloat offsetY = (scrollView.bounds.size.height > scrollView.contentSize.height)?(scrollView.bounds.size.height - scrollView.contentSize.height)/2 : 0.0;

    _imageView.center = CGPointMake(scrollView.contentSize.width/2 + offsetX,scrollView.contentSize.height/2 + offsetY);
}

- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(CGFloat)scale {
    NSLog(@"endZoom:%f", scale);
//    view.center = scrollView.center;
}

这样，就实现了图片的放大和缩小功能。
如果想要实现多张图片的功能，只需要新建一个collectionView，将上面的view添加到collectionViewCell中，这样就可以滚动浏览多张图片了