Set line height in UITextView

Note: this is not available in iOS7:

---

I have discovered that you can create a subclass that re-implements [UITextView styleString]:

@interface UITextView ()
- (id)styleString; // make compiler happy
@end

@interface MBTextView : UITextView
@end
@implementation MBTextView
- (id)styleString {
    return [[super styleString] stringByAppendingString:@"; line-height: 1.2em"];
}
@end

This is not private API usage: it is just subclassing. It's possible Apple may disagree of course (though considering how we all used to swizzle everything in order to customize UIKit appearance, I feel that this kind of “private” usage is not what Apple object to), but it's such an easy way to achieve the goals of this question that you may as well try it. Should the app be rejected you can spend the (probably significant) time on a more difficult solution.

After iOS 7, the styleString approach no longer works.

Two new alternatives are available.

Firstly, TextKit; a powerful new layout engine. To change line spacing, set the UITextView's layout manager's delegate:

textView.layoutManager.delegate = self; // you'll need to declare you implement the NSLayoutManagerDelegate protocol

Then override this delegate method:

- (CGFloat)layoutManager:(NSLayoutManager *)layoutManager lineSpacingAfterGlyphAtIndex:(NSUInteger)glyphIndex withProposedLineFragmentRect:(CGRect)rect
{
    return 20; // For really wide spacing; pick your own value
}

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Secondly, iOS 7 now supports NSParagraphStyle's lineSpacing. This gives even more control, e.g. first line indentation, and calculation of a bounding rect. So alternatively...

NSMutableParagraphStyle *paragraphStyle = [[NSMutableParagraphStyle alloc] init];
paragraphStyle.headIndent = 15; // <--- indention if you need it
paragraphStyle.firstLineHeadIndent = 15;

paragraphStyle.lineSpacing = 7; // <--- magic line spacing here!

NSDictionary *attrsDictionary =
@{ NSParagraphStyleAttributeName: paragraphStyle }; // <-- there are many more attrs, e.g NSFontAttributeName

self.textView.attributedText = [[NSAttributedString alloc] initWithString:@"Hello World over many lines!" attributes:attrsDictionary];

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FWIW, the old contentInset method to align the text along the left edge of UITextView is also no use under iOS7. Instead, to remove the margin:

textView.textContainer.lineFragmentPadding = 0;