Definitive relationship between sizeWithFont:constrainedToSize:lineBreakMode: and contentSize (text height in Objective-C)

// textView is type of UITextView

self.textView.text = @"Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat. Ut wisi enim ad minim veniam, quis nostrud exerci tation ullamcorper suscipit lobortis nisl ut aliquip ex ea commodo consequat. Duis autem vel eum iriure dolor in hendrerit in vulputate velit esse molestie consequat, vel illum dolore eu feugiat nulla facilisis at vero eros et accumsan et iusto odio dignissim qui blandit praesent luptatum zzril delenit augue duis dolore te feugait nulla facilisi. Nam liber tempor cum soluta nobis eleifend option congue nihil imperdiet doming id quod mazim placerat facer possim assum. Typi non habent claritatem insitam; est usus legentis in iis qui facit eorum claritatem. Investigationes demonstraverunt lectores legere me lius quod ii legunt saepiu开发者_运维百科s. Claritas est etiam processus dynamicus, qui sequitur mutationem consuetudium lectorum. Mirum est notare quam littera gothica, quam nunc putamus parum claram, anteposuerit litterarum formas humanitatis per seacula quarta decima et quinta decima. Eodem modo typi, qui nunc nobis videntur parum clari, fiant sollemnes in futurum.";
    
CGSize maxSize = {self.textView.contentSize.width, CGFLOAT_MAX};
CGSize computedSize = [self.textView.text sizeWithFont:self.textView.font
                                     constrainedToSize:maxSize
                                         lineBreakMode:UILineBreakModeWordWrap];
    
NSLog(@"Computed size - width:%f height:%f\nContent size - width:%f height:%f", computedSize.width, computedSize.height, self.textView.contentSize.width, self.textView.contentSize.height);

Console output:

Computed size - width:320.000000 height:450.000000

Content size - width:320.000000 height:484.000000

Why are not these values equal? At least heights.

What is the .bounds.size of the text view? If all text fits within the text view the content size can still be reported as the views full size.

The UITextView is implemented using an internal web view, with allot of private magic. It is generally not a good idea to trust the text view with anything apart from displaying and editing text. The internal measurements and calculations has, and will continues to, change between OS updates.

If what you want is to change the size of the UITextView to fit all text then you must let the text view itself do this calculation. For example:

CGRect frame = textView.frame;
frame.size.height = [textView sizeThatFits:CGSizeMake(frame.size.width, CGFLOAT_MAX)];
textView.frame = frame;