Possible to detect Bold Text setting in Settings > Accessibility?

Question

With iOS 7, it's possible to code your app to respect the user's setting for Dynamic Type - larger or smaller font sizes. You use the method preferredFontForTextStyle: and then listen to notifications in order to update the UI if the user changes the setting while your app is running. I am wondering if it's possible to do the same thing with the accessibility option "Bold Text" found in Settings > Accessibility. I realized that the Bold Text option actually requires you to restart the device, so there should be no need to listen to notifications because your app will be killed and relaunched anyways.

This is what I ultimately want to accomplish: I would like to change the navigation bar title text to a lighter style font. It may not be the default System font - it could be any font iOS can display, but I'll probably use HelveticaNeue-Light. I would also like to respect the user's preference for Bold Text. If it's enabled, I want to change the title text to a heavier weight of that same font - just like iOS does by default even though the default is already quite heavy - Helvetica Neue Medium. Indeed it does make it a little bit heavier when enabled. I want to do the same with a different font.

Here's what I'm doing to change it, but this obviously will be fixed no matter what the bold setting is:

[self.navigationController.navigationBar setTitleTextAttributes: [NSDictionary dictionaryWithObjectsAndKeys: [UIFont fontWithName:@"HelveticaNeue-Light" size:17],  [NSFontAttributeName, nil]];

I may have a solution but it seems to be a bad approach. I'm making a new font with a fixed size from the preferredFont for subheadline. This does almost exactly what I want - it automatically takes care of font-weight based on the Bold Text setting (HelveticaNeueRegular [I actually want Light] when disabled, HelveticaNeueMedium when enabled), but won't work for a different typeface. Perhaps there is a better approach?

UIFont *subtitleFont = [UIFont preferredFontForTextStyle:UIFontTextStyleSubheadline];
UIFont *titleFont = [subtitleFont fontWithSize:17];
[self.navigationController.navigationBar setTitleTextAttributes: [NSDictionary dictionaryWithObjectsAndKeys:titleFont, NSFontAttributeName, nil]];

Answer 1

As of iOS 8, it is possible to detect whether the user has enabled Bold Text in Settings using UIAccessibility.isBoldTextEnabled (docs) and UIAccessibility.boldTextStatusDidChangeNotification (docs).

For apps that also require iOS 7 support, I’ve written an elegant one-liner that works on iOS 7 & 8 with Helvetica Neue and even on iOS 9 with the San Francisco typeface, based on the fact that standard-weight fonts are commonly referred to as the “Regular” weight, and that body text uses this weight for readability:

Objective-C:

BOOL hasBoldText = ![[UIFont preferredFontForTextStyle:UIFontTextStyleBody].fontName hasSuffix:@"-Regular"];

Swift:

let hasBoldText = !UIFont.preferredFontForTextStyle(UIFontTextStyleBody).fontName.hasSuffix("-Regular")