improve device selection error messages

[satchmorun]

I'm trying out your micromidi library and when I try to run the example in the readme, I get an error when using the use method:

ruby-1.9.2-p290 :001 > require 'midi'
 => true 
ruby-1.9.2-p290 :002 > @i = UniMIDI::Input.use(:first)
NoMethodError: private method `open' called for nil:NilClass
    from /Users/rulfzid/.rvm/gems/ruby-1.9.2-p290@s10-edu/gems/unimidi-0.3.2/lib/unimidi/congruous_api_adapter.rb:147:in `use_device'
    from /Users/rulfzid/.rvm/gems/ruby-1.9.2-p290@s10-edu/gems/unimidi-0.3.2/lib/unimidi/congruous_api_adapter.rb:98:in `use'
    from (irb):2
    from /Users/rulfzid/.rvm/rubies/ruby-1.9.2-p290/bin/irb:16:in `<main>'
ruby-1.9.2-p290 :003 > @o = UniMIDI::Output.use(:first)
NoMethodError: private method `open' called for nil:NilClass
    from /Users/rulfzid/.rvm/gems/ruby-1.9.2-p290@s10-edu/gems/unimidi-0.3.2/lib/unimidi/congruous_api_adapter.rb:147:in `use_device'
    from /Users/rulfzid/.rvm/gems/ruby-1.9.2-p290@s10-edu/gems/unimidi-0.3.2/lib/unimidi/congruous_api_adapter.rb:98:in `use'
    from (irb):3
    from /Users/rulfzid/.rvm/rubies/ruby-1.9.2-p290/bin/irb:16:in `<main>'
ruby-1.9.2-p290 :004 > exit

I'm on OSX Lion, running ruby 1.9.2. Is there something I'm missing?

Another strange thing: i couldn't even get it to require 'midi' until i installed the alsa-rawmidi, midi-jruby and midi-winmm gems. The first i understand, but seems like some platform detection might not be working correctly for the latter two.

[arirusso]

Does your computer have any MIDI devices? This is what would happen if it didn't... I could probably do better error reporting there of course

You can check what devices CoreMIDI is recognizing by running "unimidi list" at the command line or UniMIDI::Device.list in Ruby

[satchmorun]

UniMIDI::Device.list returns an empty array.

I was under the impression that OSX has built-in MIDI devices. Ah, I had to turn on the IAC driver.

I'm mainly interested in the output anyway.

Sorry for another very noob question, but how do you send midi messages to headphones/speakers?

[arirusso]

OSX can route MIDI messages from one application to another but you'll need to activate that in order to see it represented with unimidi at all

Here's a blog post I did on it a while back

http://tx81z.blogspot.com/2011/06/osx-unimidi-and-midi-patch-bay.html

MIDI messages are just data -- you would need to send them to some sort of sound generator to generate sounds. For instance, sending MIDI from unimidi to Ableton Live or GarageBand would be one way to achieve this

[arirusso]

I'm going to change the title of this issue to "improve device selection error messages" and use it as a reminder to do that