较小时 UIScrollView 的中心内容 [英] Center content of UIScrollView when smaller

问题描述

我在 UIScrollView 中有一个 UIImageView 用于缩放和滚动.如果滚动视图的图像/内容大于滚动视图，则一切正常.但是，当图像变得小于滚动视图时，它会粘在滚动视图的左上角.我想让它居中，就像照片应用程序一样.

I have a UIImageView inside a UIScrollView which I use for zooming and scrolling. If the image / content of the scroll view is bigger than the scroll view, everything works fine. However, when the image becomes smaller than the scroll view, it sticks to the top left corner of the scroll view. I would like to keep it centered, like the Photos app.

关于在 UIScrollView 较小时保持内容居中的任何想法或示例?

Any ideas or examples about keeping the content of the UIScrollView centered when it's smaller?

我正在使用 iPhone 3.0.

I am working with iPhone 3.0.

下面的代码几乎可以工作.如果我在达到最小缩放级别后捏住图像，图像将返回到左上角.

The following code almost works. The image returns to the top left corner if I pinch it after reaching the minimum zoom level.

- (void)loadView {
    [super loadView];

    // set up main scroll view
    imageScrollView = [[UIScrollView alloc] initWithFrame:[[self view] bounds]];
    [imageScrollView setBackgroundColor:[UIColor blackColor]];
    [imageScrollView setDelegate:self];
    [imageScrollView setBouncesZoom:YES];
    [[self view] addSubview:imageScrollView];

    UIImageView *imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"WeCanDoIt.png"]];
    [imageView setTag:ZOOM_VIEW_TAG];
    [imageScrollView setContentSize:[imageView frame].size];
    [imageScrollView addSubview:imageView];

    CGSize imageSize = imageView.image.size;
    [imageView release];

    CGSize maxSize = imageScrollView.frame.size;
    CGFloat widthRatio = maxSize.width / imageSize.width;
    CGFloat heightRatio = maxSize.height / imageSize.height;
    CGFloat initialZoom = (widthRatio > heightRatio) ? heightRatio : widthRatio;

    [imageScrollView setMinimumZoomScale:initialZoom];
    [imageScrollView setZoomScale:1];

    float topInset = (maxSize.height - imageSize.height) / 2.0;
    float sideInset = (maxSize.width - imageSize.width) / 2.0;
    if (topInset < 0.0) topInset = 0.0;
    if (sideInset < 0.0) sideInset = 0.0;
    [imageScrollView setContentInset:UIEdgeInsetsMake(topInset, sideInset, -topInset, -sideInset)];
}

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView {
    return [imageScrollView viewWithTag:ZOOM_VIEW_TAG];
}

/************************************** NOTE **************************************/
/* The following delegate method works around a known bug in zoomToRect:animated: */
/* In the next release after 3.0 this workaround will no longer be necessary      */
/**********************************************************************************/
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale {
    [scrollView setZoomScale:scale+0.01 animated:NO];
    [scrollView setZoomScale:scale animated:NO];
    // END Bug workaround

    CGSize maxSize = imageScrollView.frame.size;
    CGSize viewSize = view.frame.size;
    float topInset = (maxSize.height - viewSize.height) / 2.0;
    float sideInset = (maxSize.width - viewSize.width) / 2.0;
    if (topInset < 0.0) topInset = 0.0;
    if (sideInset < 0.0) sideInset = 0.0;
    [imageScrollView setContentInset:UIEdgeInsetsMake(topInset, sideInset, -topInset, -sideInset)];
}

推荐答案

目前我正在继承 UIScrollView 并覆盖 setContentOffset: 以根据 调整偏移量内容大小.它适用于捏合和程序缩放.

Currently I'm subclassing UIScrollView and overriding setContentOffset: to adjust the offset based on contentSize. It works both with pinch and programatic zooming.

@implementation HPCenteringScrollView

- (void)setContentOffset:(CGPoint)contentOffset
{
    const CGSize contentSize = self.contentSize;
    const CGSize scrollViewSize = self.bounds.size;

    if (contentSize.width < scrollViewSize.width)
    {
        contentOffset.x = -(scrollViewSize.width - contentSize.width) / 2.0;
    }

    if (contentSize.height < scrollViewSize.height)
    {
        contentOffset.y = -(scrollViewSize.height - contentSize.height) / 2.0;
    }

    [super setContentOffset:contentOffset];
}

@end

除了短小精悍之外，这段代码比@Erdemus 解决方案产生了更平滑的缩放效果.您可以在 RMGallery 演示中看到它的实际效果.

In addition to being short and sweet, this code produces a much smoother zoom than @Erdemus solution. You can see it in action in the RMGallery demo.

这篇关于较小时 UIScrollView 的中心内容的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！