如果在滚动视图下面有一个视图，则调整滚动视图缩进不起作用

Question

I am working in a storyboard, in Xcode 5.0.1, making an app for iOS 7.

I have a view controller with a scroll view being displayed inside a navigation controller with a toolbar on the bottom.

The scrollview insets properly, and scrolls properly under the top and bottom bars with Adjusts Scroll View Insets enabled.

I want to add a background image that does not scroll behind the scroll view. When I do this, it's as if the Adjusts Scroll View Insets flag is unchecked, the scroll bar and the content go behind the top and bottom bars all the time.

It doesn't matter if I put the view in the storyboard, or do it programaticaly in ViewDidLoad, or ViewWillAppear, or if I put it in at a higher point in the story board and then move it to the back programatically, I get the same result, the scroll does not adjusts for the bars.

If I load or move it in viewDidAppear then it works, but that's too late for my transitions, I need the view in the background by the time it begins to become visible.

I suspect this is a bug with ios7, are there any known workarounds?

Answer 1

I faced the same problem and the solution is not straightforward. What I did was subclass the UIScrollView, add a sublayer with the image to it and move it along with the scroll. I'm sure there are better ways to do what I did, but it works.

This is ScrollViewWithBackgroundImage.m. I'm not using arc, if you are, just remove the dealloc method and change 'retain' with 'strong'. Also, you will need to add #import <QuartzCore/QuartzCore.h> if you don't do it already.

#import "ScrollViewWithBackgroundImage.h"

@interface ScrollViewWithBackgroundImage()
@property (nonatomic, retain) CALayer *backgroundLayer;
@end

@implementation ScrollViewWithBackgroundImage

- (void)setBackgroundImage:(UIImage *)image {
    CALayer *backgroundImageLayer = [CALayer layer];
    backgroundImageLayer.contents = (id)[image CGImage];
    backgroundImageLayer.bounds = self.bounds;
    backgroundImageLayer.position = self.center;
    [self.layer insertSublayer:backgroundImageLayer atIndex:0];

    self.backgroundLayer = backgroundImageLayer;
    [self setNeedsLayout];
}

-(void)layoutSubviews {
    [super layoutSubviews];

    CGRect frame = self.bounds;
    frame.origin = [self convertPoint:self.bounds.origin toView:self];
    [CATransaction begin];
    [CATransaction setValue:(id)kCFBooleanTrue forKey:kCATransactionDisableActions];
        self.backgroundLayer.frame = frame;
    [CATransaction commit];
}

- (void)dealloc {
    [_backgroundLayer release];
    [super dealloc];
}

@end

And ScrollViewWithBackgroundImage.h

@interface ScrollViewWithBackgroundImage : UIScrollView

- (void)setBackgroundImage:(UIImage *)image;

@end

Then, in the view controller:

- (void)viewDidLoad {
    [super viewDidLoad];

    // The rest of your viewDidLoad method...

    [self.scrollView setBackgroundImage:[UIImage imageNamed:@"bk.default.png"]];
}

Edit: The cause of the problem is that automaticallyAdjustScrollViewInsets property will only work if the scroll view is the first subview in the stack. You can embed the scroll view in a view and it will still work as long as the scroll view is at the bottom of the stack (at the top in interface builder). Whenever you add another subview that is below the scrollview the automatic inset adjustment will stop working.