How to make subscripts and superscripts using NSAttributedString?

Question

I need to make subscripts for chemistry formulas (H2O, Na^2+, etc)?

Is this possible to do with NSAttributedString, or is there an alternative/easier way to make subscripts?

Answer 1

Here's what I did in iOS 6. First add the CoreText, and QuartzCore frameworks. Then import:

#import <QuartzCore/QuartzCore.h>
#import <CoreText/CTStringAttributes.h>
#import <CoreText/CoreText.h>

I made a small function that inputs a plain NSString and exports a NSMutableAttributedString with the last character in superscript. This can be modified to allow setting superscript or subscript, change kCTSuperscriptAttributeName value to -1. Also you could add a variable to specify where to put the superscript in the string. Right now it just assumes the end of the string.

- (NSMutableAttributedString *)plainStringToAttributedUnits:(NSString *)string;
{
    NSMutableAttributedString *attString = [[NSMutableAttributedString alloc] initWithString:string];
    UIFont *font = [UIFont systemFontOfSize:10.0f];
    UIFont *smallFont = [UIFont systemFontOfSize:9.0f];

    [attString beginEditing];
    [attString addAttribute:NSFontAttributeName value:(font) range:NSMakeRange(0, string.length - 2)];
    [attString addAttribute:NSFontAttributeName value:(smallFont) range:NSMakeRange(string.length - 1, 1)];
    [attString addAttribute:(NSString*)kCTSuperscriptAttributeName value:@"1" range:NSMakeRange(string.length - 1, 1)];
    [attString addAttribute:(NSString*)kCTForegroundColorAttributeName value:[UIColor blackColor] range:NSMakeRange(0, string.length - 1)];
    [attString endEditing];
    return attString;
}

Now when I want to use it I can do the following to put it in a UITextField:

    NSString *qlwUnitsPlainText = @"m3";
    self.quantityLoadWeightUnits_textField.attributedText = [self plainStringToAttributedUnits:qlwUnitsPlainText];

I hope this helps somebody else, there's not many examples out there!