UIFont initialiser returns object and crashes the app

Question

My iOS app is crashing on iOS 8.2 and working perfectly on iOS 9 and above. When I checked the crash log, the following function causes the crash (Written in the NSMutableAttributedString extension)

func changeFont(font: UIFont, range : NSRange, keepFontSize: Bool = false)
{
    let traits     = font.fontDescriptor().symbolicTraits
    let descriptor = baseDescriptor.fontDescriptorWithSymbolicTraits(traits)

    let newFont    = UIFont(descriptor: descriptor, size: keepFontSize ? descriptor.pointSize : baseDescriptor.pointSize)

    self.removeAttribute(NSFontAttributeName, range: range)
    self.addAttribute(NSFontAttributeName, value: newFont, range: range) // <- Crash happens here
}

Crash Log

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'NSConcreteMutableAttributedString addAttribute:value:range:: nil value'

When I debugged and logged the variables used in that function, the descriptor & newFont both shown as <uninitialized>

(lldb) po traits
▿ UIFontDescriptorSymbolicTraits
  - rawValue : 268435458            

(lldb) po baseDescriptor
UICTFontDescriptor <0x7fc075b574c0> = {
    NSFontNameAttribute = CenturyGothic;
    NSFontSizeAttribute = 14;
}

(lldb) po descriptor
 <uninitialized>

(lldb) po keepFontSize
true

(lldb) po newFont
 <uninitialized>

I can't use if let or newFont != nil check here, because both will throw an error saying "UIFont won't be nil". How can I fix this crash ? (Or How can I check an object is initialized or not ?) I'm really stuck on this issue, since majority of my users still use iOS 8.

@WilsonXJ: Sorry, that was a typo. Actually it is `NSMutableAttributedString` — Midhun MP, May 23 '16 at 08:55
what is baseDescriptor， it can be nil ? or other situations — Wilson XJ, May 23 '16 at 08:57
@WilsonXJ: Please check the `po` debug logs. It is not nil, it is a UIFontDescriptor object — Midhun MP, May 23 '16 at 08:59

UIFont initialiser returns object and crashes the app

0 Answers0