UIScrollView结合UIImageView实现图片缩放

实现UIImageView的图片缩放功能，需要结合UIScrollView实现。

示例代码

// 定义缩放比例
CGFloat scaleMini = 1.0;
CGFloat scaleMax = 3.0;

// 主视图 UIScrollView
UIScrollView *scrollView = [[UIScrollView alloc] initWithFrame:self.view.bounds];
[self.view addSubview:scrollView];
scrollView.pagingEnabled = YES;
scrollView.backgroundColor = [UIColor redColor];
scrollView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;

// 图片视图及子视图UIScrollView
//
    NSArray *images = @[@"001.jpg", @"002.jpg", @"003.jpg", @"004.jpg"];
    //
    [images enumerateObjectsUsingBlock:^(id  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
        UIImage *image = [UIImage imageNamed:obj];
        UIImageView *imageView = [[UIImageView alloc] initWithImage:image];
        imageView.contentMode = UIViewContentModeScaleAspectFit;
        imageView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
        // 双击实现缩放
        UITapGestureRecognizer *doubleTapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self  action:@selector(handleDoubleTap:)];
        [doubleTapGesture setNumberOfTapsRequired:2];
        imageView.userInteractionEnabled = YES;
        [imageView addGestureRecognizer:doubleTapGesture];
        //
        UIScrollView *subScrollerView = [[UIScrollView alloc] initWithFrame:CGRectMake((idx * scrollView.frame.size.width), 0.0, scrollView.frame.size.width, scrollView.frame.size.height)];
        [scrollView addSubview:subScrollerView];
        subScrollerView.delegate = self;
        [subScrollerView setMinimumZoomScale:scaleMini];
        [subScrollerView setMaximumZoomScale:scaleMax];
        //
        imageView.frame = subScrollerView.bounds;
        [subScrollerView addSubview:imageView];
    }];

// 根据图片数组重置主视图contentSize
scrollView.contentSize = CGSizeMake((images.count * scrollView.frame.size.width), scrollView.frame.size.height);

// 双击缩放响应
BOOL isScaleBig = NO;
- (void)handleDoubleTap:(UITapGestureRecognizer *)recognizer
{
    UIImageView *imageView = (UIImageView *)recognizer.view;
    UIScrollView *scrollView = (UIScrollView *)imageView.superview;
    
    // 放大缩小
    CGFloat scale = scrollView.zoomScale;
    if (isScaleBig) {
        [scrollView setZoomScale:scale / scaleMini animated:YES];
        isScaleBig = false;
    } else {
        [scrollView setZoomScale:scale * scaleMini animated:YES];
        isScaleBig = true;
    }
}

// 设置协议UIScrollViewDelegate，并实现协议方法
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
    for (UIView *view in scrollView.subviews) {
        if ([view isKindOfClass:[UIImageView class]]) {
            isScaleBig = !isScaleBig;
            return view;
        }
    }
    return nil;
}

- (void)scrollViewDidZoom:(UIScrollView *)scrollView
{
    for (UIView *view in scrollView.subviews) {
        if ([view isKindOfClass:[UIImageView class]]) {
            [self showInCenter:scrollView imageView:view];
        }
    }
}

- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(CGFloat)scale
{
    // 缩放效果 放大或缩小
    if (scrollView.minimumZoomScale >= scale) {
        [scrollView setZoomScale:scaleMini animated:YES];
    }
    if (scrollView.maximumZoomScale <= scale) {
        [scrollView setZoomScale:scaleMax animated:YES];
    }
}

// 缩放时居中显示处理
- (void)showInCenter:(UIScrollView *)scrollView imageView:(UIImageView *)imageView
{
    // 居中显示
    CGFloat offsetX = (scrollView.bounds.size.width > scrollView.contentSize.width) ? (scrollView.bounds.size.width - scrollView.contentSize.width) * 0.5 : 0.0;
    CGFloat offsetY = (scrollView.bounds.size.height > scrollView.contentSize.height) ?
    (scrollView.bounds.size.height - scrollView.contentSize.height) * 0.5 : 0.0;
    imageView.center = CGPointMake(scrollView.contentSize.width * 0.5 + offsetX, scrollView.contentSize.height * 0.5 + offsetY);
}