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I have a UIScrollView that contains several dynamically resizing subviews. I can resize and layout the subviews just fine, but when I set the content size of the scroll view itself, the bottom subviews are clipped. Is there some reason why a scroll view's content size height should be larger than the sum of the heights of the views it contains?

Here's my situation in more detail: I have a superview containing a UIScrollView containing several subviews. In the superview's layoutSubviews method, I calculated the needed size of each subview, then set the frames so the subviews are tiled vertically down the screen with a bit of space between them. When done, I set the height of the UIScrollView's content size to be the end of the last subview (origin.y + size.height). In theory, this means the bottom of the scroll view's content area should exactly line up with the bottom of the last subview.

But it doesn't. Instead, a nice chunk of the last subview is clipped. It's still there - if I scroll down I can see the remaining portion during the "bounce". The problem is even worse in landscape mode - a much larger portion of the bottom subview simply isn't visible.

The subviews are all being arranged and positioned properly. The problem is that the UIScrollView's contentSize seems to need to be significantly larger than the sum of the heights of the subviews (plus the space between them). This doesn't make any sense to me. Furthermore, the amount the size is "off" varies - I reuse this view several times with different subviews, and they're all off by a different amount. Therefore, simply adding a constant to the content view height won't help.

What is causing the content size (or my height calculations) to not function correctly?

Code:

- (void)layoutSubviews
{
    [super layoutSubviews];

    CGFloat width = self.bounds.size.width - [self subviewLeftMargin] - [self subviewRightMargin]; // All subviews have same width as parent view

    CGFloat x = [self subviewLeftMargin]; // All subviews should start at the far left of the view 
    CGFloat y = [self spaceBetweenSubviews]; // Running tally of the y coordinate for the next view

    /* Adjust the subviews */
    for(UIView *view in self.theVariousSubviews) {  
        /* Resize the view with the desired width, then let it size its height as needed */
        view.frame = CGRectMake(view.frame.origin.x, view.frame.origin.y, width, view.frame.size.height);
        CGSize newSize = [view sizeThatFits:view.frame.size];

        /* Set the origin */
        //The subviews are positioned correctly, so this doesn't seem to be a problem
        view.frame = CGRectMake(x, y, newSize.width, newSize.height);

        /* Have the view refresh its own layout */
        [view setNeedsLayout];

        /* Update the y value for the next subview */
        y += newSize.height + [self spaceBetweenSubviews];
    }

    /* Resize the scroll view to ensure it fits all of the content */
    CGFloat scrollViewHeight = y;
    self.scrollView.contentSize = CGSizeMake(self.scrollView.contentSize.width, scrollViewHeight);
    //Content size is set to the same total height of all subviews and spacing, yet it is too small. Why?
}
Cellentel
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1 Answers1

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hi it seems to me that your calculation and resizing timing is wrong. Without the missing code for the layout change I could not fully understand the problem.

What strikes me is that you are assigning view.frame twice and between the new calculation you intercept the process with sublayouting which might change some of the values your calculation is depending on.

I could only advice you to separate the calculation from layouting and not invoke methods while you are calculating. To bring light into it you should either drop a sample app with the missing calculation or for yourself add some NSLog statement showing you the frame origin size of any subview and the contentOffset for the scrollview. On my experiences the scrollview is working properly in general so I would expect a bug within your code.

iOS
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