Redraw subviews after UIScrollView zoom

问题:

I've got a UIScrollView with a child UIView (CATiledLayer) - then I have a bunch more child views of that view (some of which are UITextViews)

After zooming everything is all fuzzy.

I have read various articles on the subject and they all seem to indicate that I must handle scrollViewDidEndZooming then 'do some transform stuff, mess with the frame and tweak the content offset'. Please can someone put me out of my misery and explain how this is meant to work.

Thanks in advance...

回答1:

I had a similar problem where I needed zooming with text. Mine wasn't using the CATiledLayer, so this may or may not work for you. I also wasn't using ARC, so if you are, you'll have to adjust that as well.

The solution I came up with was to set the UIScrollViewDelegate methods as follows this:

// Return the view that you want to zoom. My UIView is named contentView.
-(UIView*) viewForZoomingInScrollView:(UIScrollView*)scrollView {
  return self.contentView;
}

// Recursively find all views that need scaled to prevent blurry text
-(NSArray*)findAllViewsToScale:(UIView*)parentView {
    NSMutableArray* views = [[[NSMutableArray alloc] init] autorelease];
    for(id view in parentView.subviews) {

        // You will want to check for UITextView here. I only needed labels.
        if([view isKindOfClass:[UILabel class]]) {
            [views addObject:view];
        } else if ([view respondsToSelector:@selector(subviews)]) {
            [views addObjectsFromArray:[self findAllViewsToScale:view]];
        }
    }
    return views;
}

// Scale views when finished zooming
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale {
    CGFloat contentScale = scale * [UIScreen mainScreen].scale; // Handle retina

    NSArray* labels = [self findAllViewsToScale:self.contentView];
    for(UIView* view in labels) {
        view.contentScaleFactor = contentScale;
    }
}

回答2:

I hit the same problem and the code above didn't work for my case. Then I followed the documentation:

If you intend to support zoom in your scroll view, the most common technique is to use a single subview that encompasses the entire contentSize of the scroll view and then add additional subviews to that view. This allows you to specify the single ‘collection’ content view as the view to zoom, and all its subviews will zoom according to its state.

"Adding Subviews" section of https://developer.apple.com/library/ios/#documentation/WindowsViews/Conceptual/UIScrollView_pg/CreatingBasicScrollViews/CreatingBasicScrollViews.html

I simply created an empty view and added my CATiledLayer and all other subviews to that empty view. Then added that empty view as the only child view of the scroll view. And, it worked like a charm. Something along these lines:

- (void)viewDidLoad
{
    _containerView = [[UIView alloc] init];
    [_containerView addSubView:_yourTiledView];
    for (UIView* subview in _yourSubviews) {
        [_containerView addSubView:subview];
    }
    [_scrollView addSubView:_containerView];
}

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