UITextView visually changing content position when pasting in text - iphone

Question

I have a UITextView which is designed to enlarge to fit the contentView when needed. When I paste in a paragraph of text, however, it puts the start and end points of the content vertically in the wrong places. Entering or deleting a character resets it back to the correct position.
Any ideas why this is?
-(void)textViewDidChange:(UITextView *)textView {
self.textView.frame = CGRectMake(
self.textView.frame.origin.x,
self.textView.frame.origin.y,
self.textView.frame.size.width,
self.textView.contentSize.height + HEADER_ADDITIONAL_HEIGHT);
self.textView.contentOffset = CGPointMake(0, 0);
self.previousContentSize = textView.contentSize;
}

Answer 1

When I used:
textView.contentSize = textView.frame.size;
textView.contentOffset = CGPointZero;
It solved my issue, but created a new issue where we sometimes get weird scrolling while typing or deleting text. So, I used this:
textView.contentSize = CGSizeMake( textView.contentSize.width,
textView.contentSize.height+1);
This also solved the issue. I think what we all need here is the effect which we get whenever the contentSize of a textview is changed. Unfortunately, I do not know what this effect is. If somebody knows, please tell.
Update:
I have found a method which you can use to solve your issue (I used this to resolve mine).
You can ask NSLayoutMAnager to refresh the entire layout:
[textView.textStorage edited:NSTextStorageEditedCharacters range:NSMakeRange(0, textView.textStorage.length) changeInLength:0];
NSLayoutManager attempts to avoid refreshing the layout because it's time consuming and takes a lot of work, so it's set up to only do it when absolutely necessary (lazily).
There are a number of invalidateLayout functions related to this class but none of them cause an actual re-layout when called.

Answer 2

I know this comes late, but I ran into this issue and thought I should share what I came up with in case others find themselves in the same situation.
You are on the right track, but in textViewDidChange: you are missing one important thing: setting the contentSize after updating the frame height.
// I used 0.f for the height, but you can use another value because according to the docs:
// "the actual bounding rectangle returned by this method can be larger
// than the constraints if additional space is needed to render the entire
// string. Typically, the renderer preserves the width constraint and
// adjusts the height constraint as needed."
CGSize size = CGSizeMake(textview.frame.size.width, 0.f);
CGRect rect = [string boundingRectWithSize:size
options:OptionsYouNeedIfAny // NSStringDrawingOptions
context:nil];
// Where MinTextViewHeight is the smallest height for a textView that
// your design can handle
CGFloat height = MAX(ceilf(rect.size.height), MinTextViewHeight);
CGRect rect = textView.frame;
rect.size.height = height;
textView.frame = rect;
// Adjusting the textView contentSize after updating the frame height is one of the things you were missing
textView.contentSize = textView.frame.size;
textView.contentOffset = CGPointZero;
I hope this helps!
See the docs for more info about using boundingRectWithSize:options:context:.