[Kde-bindings] Signal-slot with hash param

[Stefano Crocco]

On Monday 03 October 2011 03:21:58 Enrico Pilotto wrote:
> Hi,
>   Im using qtbindings for ruby (https://github.com/ryanmelt/qtbindings)
> and i would emit a signal with an hash param...
> 
> Something like this:
> 
> #----------------------
> require 'Qt'
> 
> class Foo < Qt::Object
> 
>   signals 'my_signal(Hash)'
>   slots 'my_slot(Hash)'
> 
>   def initialize(parent = nil)
>     super(parent)
>     connect(self, SIGNAL('my_signal(Hash)'), self, SLOT('my_slot(Hash)'))
>   end
> 
>   def emit_my_signal
>     emit my_signal({:foo => :bar})
>   end
> 
>   def my_slot(hash)
>     puts hash.inspect
>   end
> end
> 
> o = Foo.new
> o.emit_my_signal
> #----------------------
> 
> If I run this script I get the error: Cannot handle 'Hash' as slot
> argument (ArgumentError).
> If I use int instead of Hash everything is fine.
> 
> There is a way to do this?? How?
> 
> Thanks.

Unfortunately, QtRuby only supports signals and slots having C++ types as 
arguments. This means you can use ruby booleans, integer, floats, strings and 
all Qt classes as arguments, because they correspond to some C++ class (and 
even in this case, note that you have to use the C++ name of the type in the 
call to connect, not the ruby name. For example, you need to use QString 
instead of the ruby String class name). Hashes don't have a corresponding 
class in C++ (actually, Qt does have a QHash class, but I don't think it's 
supported).

According to the QtRuby site [1], you have two possible way of emitting (and 
connecting to) ruby classes. One is to use a signal which takes as argument 
the object_id of the object (which is an int) and retrieve the object itself 
in the slot using ObjectSpace._id2ref. I find this quite ugly, however. The 
other option is to have a signal using a Qt::Variant as argument and wrap your 
object in it using Qt::Variant.from_value, then unwrap it in your slot using 
Qt::Variant#value.

I hope this helps

Stefano

[1] http://techbase.kde.org/Development/Languages/Ruby#Emitting_Ruby_Classes