iPhone-在iPad上的UIScrollView中无法缩放/图像放置

Question

I am having trouble with my ScrollView. I am programmatically adding a subview UIImageView to the ScrollView, and the implementing zoom. I was having no trouble on the iPhone using the code below to center the image, but on the iPad the image is off to the right and shoved down. I added the storyboard for iPad and an empty view controller and hooked it up, just like I did for iPhone. I don't have a ScrollView subclass (so simple, I did not think it was needed).

How do I get the image/scrollview to be centered on the iPad?

Code: I don't specify location or size anywhere else in the code

This is all in my viewcontroller.m

//Create scrollView.
    _scrollView = [[UIScrollView alloc] initWithFrame:[[self view] bounds]];
    [_scrollView setBackgroundColor:[UIColor whiteColor]];
    [_scrollView setDelegate:self];
    [_scrollView setBouncesZoom:YES];
    [[self view] addSubview:_scrollView];

//Add violinImage to scrollView
    _currentImage = [[UIImageView alloc] initWithImage:[UIImage imageNamed:_currentImageName]];
    [_scrollView setContentSize:[_currentImage frame].size];
    [_scrollView addSubview:_currentImage];

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
    return _myImage;
}

- (void)scrollViewDidZoom:(UIScrollView *)scrollView
{
    UIView *subView = [scrollView.subviews objectAtIndex:0];
    CGFloat offsetX;
    CGFloat offsetY;
    if (IS_IPAD)
    {
        offsetX = (scrollView.bounds.size.width - scrollView.contentSize.width) /2;
        offsetY = scrollView.bounds.size.height * 0.3;
    }
    else
    {
        if (scrollView.bounds.size.width > scrollView.contentSize.width) {
            offsetX = (scrollView.bounds.size.width - scrollView.contentSize.width) * 0.5;
        }
        else
        {
            offsetX = 0.0;
        }

        if (scrollView.bounds.size.height > scrollView.contentSize.height)
        {
            offsetY = (scrollView.bounds.size.height - scrollView.contentSize.height) * 0.5;
        }
        else
        {
            offsetY = 0.0;
        }
    }
    subView.center = CGPointMake(scrollView.contentSize.width * 0.5 + offsetX, scrollView.contentSize.height * 0.5 + offsetY);
}

Thank you!

Answer 1

So this is sort of a unique case for me, but on the iPad, my image was not larger than the scrollview frame after zoom. A part of code I did not show in my original question because I did not think it was relevant. Whoops.

It worked on the iPhone, because my image was always larger than the frame, so it did not apply any offset, and centered the scrollview (and contents). On the iPad I was getting an offset value with the iPhone math, so I needed to reverse the offset calculation.

Here is what I did when setting the zoom to get it to work.

if (IS_IPAD && IS_RETINA) {
        float topInset = (imageSize.height - maxSize.height) / 2.0;
        float sideInset = (imageSize.width - maxSize.width) / 2.0;
        if (topInset < 0.0) topInset = 0.0;
        if (sideInset < 0.0) sideInset = 0.0;
        [_scrollView setContentInset:UIEdgeInsetsMake(topInset, sideInset, -topInset, -sideInset)];
    }
    else
    {
        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;
        [_scrollView setContentInset:UIEdgeInsetsMake(topInset, sideInset, -topInset, -sideInset)];
    }