scaledValueForValue: called on a font that doesn’t have a text style set

This problem has been fixed in iOS 8.1.

Instead of spending time building a custom header/footer view, I just not apply the custom font to devices running iOS 8.0. Most people will probably have updated to iOS 8.1 anyway.

I use the following code for this:

NSOperatingSystemVersion iOS_8_1 = (NSOperatingSystemVersion){8, 1, 0};

if (![[NSProcessInfo processInfo] respondsToSelector:@selector(isOperatingSystemAtLeastVersion:)]
    || [[NSProcessInfo processInfo] isOperatingSystemAtLeastVersion:iOS_8_1]) {
    header.textLabel.font = [UIFont fontWithName:@"Avenir-Medium" size:header.textLabel.font.pointSize];
}

The first statement is true if the device is running an iOS version lower than 8 (since isOperatingSystemAtLeastVersion: was introduced in iOS 8.0). The second statement is true if the device if running iOS 8.1 or later. With both statements we thus only exclude devices running iOS 8.0.