UIScrollView ScrollRectToVisible - not working with animate = yes

Question

I have a UIScrollView which contains a button. When the button is pressed, I would like to scroll to the bottom of the view using scrollRectToVisible.

eg:

CGRect r = CGRectMake(0, myUIScrollView.contentSize.height - 1, 1, 1);
[myUIScrollView scrollRectToVisible:r animated:YES];

If I set animated to NO, everything works as expected, but if I set it to YES, I see really weird behaviour:

• basically, nothing happens.
• if I tap the button repeatedly, it may scroll a couple pixels, or may scroll all the way.
• but if I scroll the view manually with a finger before pressing the button, it has a chance of scrolling to the bottom as expected, but it's not a sure thing.

I've printed _geScroll_Settings.contentSize, and it's as-expected.

I've also tried to delay the call to scrollRectToVisible by starting a timer, but the results are pretty much the same.

The scrollView is fairly vanilla. I'm creating it in interface builder. I am dynamically adding the scrollView's content at startup, and adjusting it's contentSize appropriately, but all that seems to be working fine.

Any thoughts?

Answer 1

My bet is that scrollRectToVisible is crapping out because the visible area is not valid (1x1), or the y offset is just outside the bounds, have you tried setting it with the size of the visible area of the scrollView instead?

CGRect rectBottom = CGRectZero;
rectBottom.size = myUIScrollView.frame.size;
rectBottom.origin.y = myUIScrollView.contentSize.height - rectBottom.size.height;
rectBottom.origin.x = 0;

[myUIScrollView scrollRectToVisible:rectBottom animated:YES];

Sorry I can't help you out more, but I'm not on my Mac right now, so I can't run a test. The code above would create a CGRect of the exact size of what fits inside the scrollView visible portion, and the offset would be the last visible portion in it.