Why does NSTextView not always wrap text fluently while resizing? - macos

Question

I've stumbled upon a behavior in NSTextView that does not seem intended, or that I at least do not understand the reasoning behind.
When you have a large body of text in an NSTextView and you resize the control/window, the wrapping of words only happens fluently and immediately while resizing when the text is scrolled near the top. If you scroll far down in the text, it does not, and it doesn't seem to "commit" the wrapping until you release and finish resizing.
Is there some internal limitation, or is this a bug?
The issue seems to be reproducible:
macOS 10.15.4, Xcode 11.4.1
Create a new macOS App project
Put an NSTextView on the default generated view controller (doesn't matter which of the 3: rich, plain or default) and constrain it so that it resizes with the window (top, bottom, leading, trailing)
Run the application and paste a large body of text into the text view (for example: http://www.gutenberg.org/cache/epub/12281/pg12281.txt)
Scroll to the top of the NSTextView and observe how the text wraps while resizing the window
Scroll to the bottom and observe how it only wraps after resizing the window
Hoping there's any Cocoa detectives out there who can provide some enlightenment on this one.
EDIT:
As per the docs, it states that "the layout manager reserves the right to perform layout for larger ranges". I take it that this means it is indeed intended as a performance consideration.
Is there any way to determine what the limit is, though?

Answer 1

EDIT: You could try subclassing NSScrollView to render the text into multiple containers.
NSTextStorage *storage = [[NSTextStorage alloc] initWithString:string];
NSLayoutManager *manager = [[NSLayoutManager alloc] init];
[storage addLayoutManager:manager];
NSInteger i = 0;
while (YES) {
NSTextContainer *container = [[NSTextContainer alloc] initWithSize:CGSizeMake(width, height)];
[manager addTextContainer:container];
NSTextView *textView = [[NSTextView alloc] initWithFrame:CGRectMake(x, y, width, height) textContainer:container];
[self.contentView addSubview:textView];
i++;
NSRange range = [manager glyphRangeForTextContainer:container];
if ( range.length + range.location == string.length )
break;
}
Then, while resizing the window, you can call NSLayoutManager to ensure the layout only for visible containers.