Re: [Fxruby-users] catching exceptions in event handlers

[Lyle J. <jl...@cf...>]

Emmanuel Touzery wrote:

>     I'm having the problem that my GUI app might have some bugs; in that
> case, instead of seeing it exiting violently, dumping the stack on the
> command line (which will never be seen by the user in most cases), i would
> like to catch the exception and display a nice dialog box.
>     Wrapping the app.run call (i don't remember how it's called, but it's
> something like that) in a begin/rescue block doesn't seem to catch this
> exception.

Is it a standard Ruby exception, or is the Ruby interpreter (ruby) 
seg-faulting? If it's the former (a regular exception), it /should/ be 
raised all the way to the "top" and get caught in your begin-rescue 
block around the call to FXApp#run.

>     So it would seem i need to wrap each event handler in a begin/rescue
> block.

You might also see if the Fox.setIgnoreExceptions() method is a suitable 
workaround; see the "Debugging Tricks" at the end of this page:

     http://www.fxruby.org/doc/differences.html

>     I thought about something like (didn't look at the code, untested
> snippet, just to give the idea):
> 
> class FXWindow
>     def connect(event, &block)
>         begin
>             super
>         rescue
>             FXMessageBox("an error occured, here is the stacktrace, contact
> the developer of the application"...)
>             exit
>         end
>     end
> end

No, this wouldn't work. The connect() method just sets up the mapping 
between a message type (e.g. SEL_COMMAND) and the block or method that 
handles it. It doesn't actually execute the code.

> and the same for other ways to connect the events (ie event tables). i would
> put that in a "exceptionfox.rb", and do a "require 'exceptionfox.rb'"
> instead of "require 'fox'", so i wouldn't have to change my code. i could
> also call a user-defined function when getting an exception.
> i didn't try this approach yet (no time). but i'm wondering if it seems
> possible, and if there is maybe a better solution?

This sounds way too complicated, IMO. If wrapping the call to FXApp#run 
with a "last-chance" begin-rescue block is failing to catch exceptions, 
I would like to see that demonstrated and get it fixed. I think the best 
solution is to get a good group of testers and get them to help you find 
the bugs ;)