How to use alternate font weights (e.g. “short”) in a WKInterfaceLabel?

Question

In Apple's Apple Watch Design Resources , there is a document called Alternate Font Weights and Italicizations . In it, it shows examples of what the default font looks like with different attributes such as Italic , Emphasized , and Short applied to it.

Assume I want to use a font that looks exactly like the "Short" example.

1. Is there any way to choose this font and style via the storyboard for a label?

2. In code, how would I set a label to use this font and style?

Answer 1

In an iOS project, I tried modifying the body font ( UIFontTextStyleBody ) to include UIFontDescriptorTraitTightLeading . When I read the fontAttributes properties, it reports the NSFontNameAttribute as .AppleSystemUIShortBody (the original value is .AppleSystemUIBody ).

From this, I was able to figure out Apple's terms:

+------------+-----------------------------------+------------------------------+---------------------------------+
|    Term    |  UIFontDescriptorSymbolicTraits   |     NSFontNameAttribute      |    NSCTFontUIUsageAttribute     |
+------------+-----------------------------------+------------------------------+---------------------------------+
|            | (none)                            | .AppleSystemUIBody           | UICTFontTextStyleBody           |
| Italic     | UIFontDescriptorTraitItalic       | .AppleSystemUIItalicBody     | UICTFontTextStyleItalicBody     |
| Emphasized | UIFontDescriptorTraitBold         | .AppleSystemUIEmphasizedBody | UICTFontTextStyleEmphasizedBody |
| Short      | UIFontDescriptorTraitTightLeading | .AppleSystemUIShortBody      | UICTFontTextStyleShortBody      |
| Tall?      | UIFontDescriptorTraitLooseLeading | .AppleSystemUISpliceTallBody | UICTFontTextStyleTallBody       |
+------------+-----------------------------------+------------------------------+---------------------------------+

If you attempt to do the same thing with UIFontDescriptorTraitExpanded , UIFontDescriptorTraitCondensed , UIFontDescriptorTraitVertical , UIFontDescriptorTraitUIOptimized , and then read the fontAttributes , it returns the same value as the Body style. If you try the same thing with UIFontDescriptorTraitMonoSpace , it returns a nil dictionary.

Therefore, in an Apple Watch project, you should be able to use the Body Short Emphasized font like so:

/*1*/ UIFontDescriptor *fontDescriptor = [UIFontDescriptor preferredFontDescriptorWithTextStyle:UIFontTextStyleBody];
/*2*/ fontDescriptor = [fontDescriptor fontDescriptorWithSymbolicTraits:UIFontDescriptorTraitTightLeading | UIFontDescriptorTraitBold];
/*3*/ UIFont *font = [UIFont fontWithDescriptor:fontDescriptor size:0];
/*4*/ [label setAttributedText:[[NSAttributedString alloc] initWithString:text attributes:@{NSFontAttributeName: font}]];

I say "should" because there are two bugs in play here:

• On line 2, UIFontDescriptorTraitTightLeading is being specified, yet this trait is ignored on both watch simulators. Bold and italic work just fine.
• On line 3, since size is set to 0 , it gets its value from the UIFontDescriptorSizeAttribute in fontDescriptor ^[1] . The problem is that on a 38mm device, there is a bug with both +[UIFontDescriptor preferredFontDescriptorWithTextStyle:] and -[UIFont preferredFontForTextStyle:] (used on line 1 ). When the user doesn't customize the font size , both methods return 16 , when clearly 15 should be chosen on the 38mm device. (You can verify this by placing a label on a storyboard, assigning it the Body size, and visually comparing it to a label that sets its size to 15 manually.)

Note: I am running Xcode 6.2.