UISCcrollView's contentSize changes after keyboard appears - iphone

Question

Basing on:
https://developer.apple.com/library/ios/#documentation/StringsTextFonts/Conceptual/TextAndWebiPhoneOS/KeyboardManagement/KeyboardManagement.html
I have implemented a feature that scrolls the view automatically whenever keyboard hides selected text input (mine and the one from tutorial are actually the same).
Unfortunately, there is an undesirable behaviour: my scrollView's contentSize property gets increased by the height of the keyboard. So when keyboard is still visible I can scroll the view, but below proper content a blank space appears. This is a thing I would like to avoid. I'm aware this is caused by changing contentInset property, so maybe there is another way to do this thing without side-effects.
At first I register observers for UIKeyboardDidShowNotification and UIKeyboardWillHideNotification:
- (void)registerKeyboardNotifications
{
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(keyboardWasShown:) name:UIKeyboardDidShowNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(keyboardWillBeHidden:) name:UIKeyboardWillHideNotification object:nil];
}
this function is called in viewWillAppear. Methods keyboardWasShown and keyboardWillBeHidden look as following:
- (void)keyboardWasShown:(NSNotification *)notification
{
NSDictionary *info = [notification userInfo];
CGSize kbSize = [[info objectForKey:UIKeyboardFrameBeginUserInfoKey] CGRectValue].size;
UIEdgeInsets contentInsets = UIEdgeInsetsMake(0.0, 0.0, kbSize.height, 0.0);
scrollView.contentInset = contentInsets;
scrollView.scrollIndicatorInsets = contentInsets;
CGRect rect = self.view.frame;
rect.size.height -= kbSize.height;
if(!CGRectContainsPoint(rect, activeField.frame.origin)) {
CGPoint scrollPoint = CGPointMake(0.0, 2*activeField.frame.size.height+activeField.frame.origin.y-kbSize.height);
[scrollView setContentOffset:scrollPoint animated:YES];
}
}
- (void)keyboardWillBeHidden:(NSNotification *)notification
{
UIEdgeInsets contentInsets = UIEdgeInsetsZero;
scrollView.contentInset = contentInsets;
scrollView.scrollIndicatorInsets = contentInsets;
}
As I wrote earlier, it is basically Apple's solution.

Answer 1

Content inset is meant to allow access to parts of the scroll view that might appear hidden below keyboard (for example). So if you had a text view on the bottom of your content, the user would not be able to interact with it, as it would be hidden beneath the keyboard window. With content inset (as per the Apple example), you are able to scroll it more, and reveal the text view. It doesn't actually increase the contentSize property.
Please read more here:
http://developer.apple.com/library/ios/#documentation/WindowsViews/Conceptual/UIScrollView_pg/CreatingBasicScrollViews/CreatingBasicScrollViews.html

Answer 2

CGFloat contentSizeHeight = contentSize.height;
CGFloat collectionViewFrameHeight = self.collectionView.frame.size.height;
CGFloat collectionViewBottomInset = self.collectionView.contentInset.bottom;
CGFloat collectionViewTopInset = self.collectionView.contentInset.top;
CGPoint bottomOffsetForContentSize = CGPointMake(0, MAX(-collectionViewTopInset, contentSizeHeight - (collectionViewFrameHeight - collectionViewBottomInset)));
[self.collectionView setContentOffset:bottomOffsetForContentSize animated:animated];