Re: Developing Qt4 applications with Ruby 1.9.x

On Wednesday 07 December 2011 Rosalind Mitchell wrote
> I am running KDE on 32-bit Linux Mint Debian Edition.  For several years now
> I have been developing Qt-based applications with Ruby 1.8.
> 
> Now I'm anxious to move forward and adopt Ruby 1.9 as urged.  I can install
> 1.9.2 from the LMDE repositories, but there doesn't appear to be any Qt4
> libraries available.  So I thought I'd go right up to date, downloading and
> compiling Ruby 1.9.3p0 from scratch, installing it in the /usr/local
> hierarchy.
> 
> I found, downloaded and extracted the latest Qt4-QtRuby build files.  This
> is where the headaches began.  Running cmake . failed immediately as cmake
> could not find Ruby.  After scratching my head and searching Google I
> established that the CMakeCache.txt file needed some tweaking.  To be
> precise, these lines needed to be filled out to allow cmake to find the
> ruby.h file and ruby executable:
> 
> //Path to a file.
> RUBY_CONFIG_INCLUDE_DIR:PATH=/usr/local/include/ruby-1.9.1/i686-linux
> 
> //Path to a program.
> RUBY_EXECUTABLE:FILEPATH=/usr/local/bin/ruby
> 
> This, then, allowed me to build and install the Qt4-QtRuby library.  But
> then, when I went to test it with a very minimal script:
> 
> #!/usr/local/bin/ruby -w
> 
> require 'Qt4'
> 
> app = Qt::Application.new(ARGV)
> 
> app.exec()
> 
> I get the response:
> 
> /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:1415: warning: mismatched
> indentations at 'end' with 'if' at 1411
> /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2527: warning: method
> redefined; discarding old method_missing
> 
> [...]
> 
> /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2527: warning: method
> redefined; discarding old const_missing
> /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:459:in `initialize':
> unresolved constructor call Qt::Application (ArgumentError)
>         from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:459:in
> `initialize'
>         from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2640:in
> `call' from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2640:in
> `block in try_initialize'
>         from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2639:in
> `catch' from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2639:in
> `try_initialize'
>         from ./qt.rb:16:in `new'
>         from ./qt.rb:16:in `<main>'
> 
> (that second warning repeated several hundred times, though I'm not all that
> concerned about that.)
> 
> The test script works fine under 1.8.7, obviously it doesn't do anything but
> it doesn't throw any warnings or errors either.
> 
> Doing the same in irb yields
> 
> irb(main):001:0> require 'Qt4'
> => true
> irb(main):002:0> app = Qt::Application.new(ARGV)
> ArgumentError: unresolved constructor call Qt::Application
> 
>         from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:459:in
> `initialize'
>         from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:459:in
> `initialize'
>         from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2640:in
> `call' from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2640:in
> `block in try_initialize'
>         from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2639:in
> `catch' from /usr/local/lib/ruby/site_ruby/1.9.1/Qt/qtruby4.rb:2639:in
> `try_initialize'
>         from (irb):2:in `new'
>         from (irb):2
>         from /usr/local/bin/irb:12:in `<main>'
> irb(main):003:0>
> 
> Enquiries on Google haven't been very fruitful, with just a suggestion that
> the fault lies in the Qt.cpp file but not much help that I could see on
> exactly what the problem is or how to fix it (my knowledge of C++ is
> sketchy at best).
> 
> I have the feeling either that I've missed something very simple, or that
> Ruby 1.9.x is not yet able to work effectively with Qt4.  Is there anybody
> here who has encountered this problem?  Should I carry on regardless with
> 1.9.3 and find another GUI interface to work with, or should I reluctantly
> revert to 1.8.7?
> 
> Rosie

qtruby works perfectly for me with ruby 1.9.3, so the answer to your last 
question is: neither. You just need to find out why qtruby isn't working for 
you. Unfortunately, I can't say what's wrong with your installation, but here 
are some possibilities which come to my mind:
* have you perhaps the version of qtruby you used with ruby 1.8.7? If so, 
maybe that's loaded instead of the new version. Try uninstalling them and see 
if anything changes
* at least with older versions of qtruby, it wasn't enough to change the two 
parameters you mention in the CMakeCache.txt file to have cmake pick up the 
correct ruby version (I don't know whether that's changed recently). To be on 
the safe side, you can do the following:
 - from the build directory (where you run cmake from) issue the command
   ccmake .
This will give you a very simple GUI where to change the parameters (rather    
than doing so by hand as it seems you've done). Press the t key to display 
advanced settings, then change the following variables (as an example, I'll 
add the values which I use on my system: they'll be different on yours, if 
only because you installed ruby 1.9 in /usr/local while I installed it in 
/usr):
 - CUSTOM_RUBY_SITE_ARCH_DIR: /usr/lib/ruby/site_ruby/1.9.1/x86_64-linux
 - CUSTOM_RUBY_SITE_LIB_DIR: /usr/lib/ruby/site_ruby/1.9.1
 - RUBY_ARCH_DIR: /usr/lib/ruby/1.9.1/x86_64-linux
 - RUBY_CONFIG_INCLUDE_DIR: /usr/include/ruby-1.9.1/x86_64-linux
 - RUBY_EXECUTABLE: /usr/bin/ruby
 - RUBY_INCLUDE_DIR: /usr/include/ruby-1.9.1
 - RUBY_LIBRARY: /usr/lib/libruby19.so
 - RUBY_RUBY_LIB_DIR: /usr/lib/ruby/1.9.1
 - RUBY_SITEARCH_DIR: /usr/lib/ruby/site_ruby/1.9.1/x86_64-linux
 - RUBY_SITELIB_DIR: /usr/lib/ruby/site_ruby/1.9.1
After changing this variables, press 'c' to configure, then 'g' to generate 
the files (ignore any warnings in these steps).

If all the above fails, you may try asking on the qtruby forum 
http://rubyforge.org/forum/forum.php?forum_id=722 or the kde-bindings mailing 
list (you can subscribe to it at
https://mail.kde.org/mailman/listinfo/kde-bindings).

By the way, where did you download qtruby from? Maybe the version you 
downloaded is not as recent as you thought!

I hope this helps

Stefano