Question

I’m trying to hook up a global exception handler using NSSetUncaughtExceptionHandler in a Rubymotion app. And I can’t figure out how to do it, probably I’m using Rubymotion function pointer syntax incorrectly.

In application(application, didFinishLaunchingWithOptions:launchOptions) I have:

NSSetUncaughtExceptionHandler nil do |exception|
  NSLog "exception handler block"
  applicationFailedWithException(exception)
end

And the handler (which is never called):

def applicationFailedWithException(exception)
  NSLog "applicationFailedWithException"
end

Then, in runtime, when some NoMethodError happens somewhere neither the exception handler block, neither the handler method are called. I’ve tried both in the Simulator and on the device — no success.

P.S. Is there a way to get the ruby methods stack in the crash log, the last application method in the crash log is always the rb_rb2oc_exc_handler instead of the app-specific method, and that’s weird.

Thanks

Update 2015

It seems that with the newer versions of the Rubymotion you have to save a references to the handler in an instance variable, otherwise it will not work. So it should look like:

def application(application, didFinishLaunchingWithOptions:launchOptions)
  @exceptionHandler = lambda { |exception| uncaughtExceptionHandler(exception) }

  # or you can use a method reference, which is the same
  # @exceptionHandler = method :uncaughtExceptionHandler

  NSSetUncaughtExceptionHandler @exceptionHandler

  ...
end

def uncaughtExceptionHandler(exception)
  # log it or send it to crashlytics / flurry / whatever
  NSLog "Fatal exception catched\nName: #{exception.name}\nReason: # {exception.reason}\nInfo#{exception.userInfo}"
end

Answer 1

To get this to work, I had to assign a block to a variable, then use that variable:

handler = lambda do |exception|
  NSLog "Exception Name: #{exception.name}"
end
NSSetUncaughtExceptionHandler(handler)

If I then punch in something like NSException.raise("test", format: "test") in the REPL, I’ll see NSLog do it’s thing:

2012-09-11 09:33:05.949 exc[14723:c07] Exception Name: test
2012-09-11 09:33:05.950 exc[14723:c07] *** Terminating app due to uncaught exception 'test', reason: 'test'
*** First throw call stack:
(0x1647022 0x22bcd6 0x15efa48 0x15ef9b9 0x8f00743 0xe3c0c 0x8f0031a 0x8f000ad 0xd4c9fa2 0x259e8d9 0x259f509 0x157e803 0x157dd84 0x157dc9b 0x261f7d8 0x261f88a 0x563626 0x25d0 0x23b5)
terminate called throwing an exception%                                                                                 

Theoretically, you should be able to nest the lambda directly as the parameter rather than assigning it to a variable first, but I don’t think RubyMotion properly retains the block and the application crashes without error if you try it.