Re: [Rubycocoa-talk] Can't "assign" an NSError to an ObjcPtr

[Allison N. <dem...@ma...>]

Hmmm, not really. The best resource for explaining the bridge is Brian  
Marick's book, and the source code.  Some of the answers I gave you  
yesterday were based on directly reading the source code for  
RubyCocoa.  Sometimes I know what to do because I have seen how it was  
done in other people's RubyCocoa code.  The example code in /Developer/ 
Examples/RubyCocoa is a very good resource.  You can also try googling  
the method name using RubyCocoa syntax. For example, I learned about  
errors being returned when I was trying to work with QTKit.  So I  
googled "QTMovie.movieWithFile_error" and found this:

http://images.apple.com/server/macosx/docs/Podcast_Producer_Workflow_Tutorial.pdf

which has this code in it:
# Load the first movie.
first_input_movie, error =
OSX::QTMovie.movieWithFile_error(first_input_path)
# Check to see if the first movie opened successfully.
if first_input_movie == nil or error != nil
   $stderr.puts "could not load first movie"
   exit(1)
end

The last thing I can think of is to follow Brian's philosophy.  If you  
are not sure how things work, try running a test case to see.  For  
example, for your question about NSDictionary/Hash, the best thing to  
do is to try the ruby way and see if it works.  If not, use the Cocoa  
way.

I still find that the best thing to do is to read the source code, but  
then I am a very experienced C programmer, with a fair amount of  
experience in generating C/Ruby bindings, so it's fairly easy for me  
to do that.

Of course, if you get stuck, that's what the mailing list is for....

Alli

Le 17 févr. 10 à 21:01, Wolfgang Kittenberger a écrit :

> Hi Allison,
>
>  I like this answer!  It explains, why I was not able the get that  
> "17 liner" working.
>
>  To explain the background: I try to write the examples from the  
> Hillegass book (Cocoa Programming ..., 3. ed) in RubyCocoa. And I  
> have to admit, that my Objective-C and Cocoa knowledge is very  
> limited.
>
>   In chapter 20 he writes a view to a PDF file and checks then if it  
> worked:
>
>   ...
>   NSError *error;
>   BOOL successful = [data writeToFile: path
> 						options:0
> 						error:&error];
>   if (!successful) {
> 	NSAlert *a = [NSAlert alertWithError:error];
>        [a runModal];
>   }
>  ...
>
>   My naive approach to test the code for the error branch was to  
> generate the error by myself.  This brought me to use ObjcPtr#assign  
> to set the errorpointer as described in my mail.
>
>  When this did not work, I looked for descriptions for the ObjcPtr  
> class. But I did not find it. I had a look in the source of  
> "cls_objcptr.m", but it was double dutch for me.
>
>  The I tried to generate the bridge-doc, which did not work. After  
> your hints I did this with the last but one versions of RubyCocoa  
> (0.13.2) and OSX(10.5.8). Then I was really disappointed, as I did  
> not find there anything about
> my challenge.
>
>  Now after your explanations I can see, that I was complete on the  
> wrong way. I did not understand, that NSAlert.alertWithError expects  
> not what I tried to construct (and failed). I even did not realize,  
> that there existst something like a Ruby NSError.
>
>  I learned in the RubyCocoa book from Brian Marick, that there is a  
> Ruby NSRange, but I did not find anything about error handling. But  
> due to my long years programming experience, I am convinced that  
> checking errors is essential.
>
>  So can you recommend some reading to get informations as gave it in  
> your mail, like where I can expect the RubyCocoa bridge to convert  
> Ruby objects to NS objects, and where I have to do it myself (e.g.  
> NSDictionary instead of a Ruby hash, or NSString.stringWithString  
> instead of a Ruby string)? Is the link "http://rubycocoa.sourceforge.net/HowDoesTheBridgeWork 
> " the only resource?
>
> Best regards
> Wolfgang
>
> P.S.:
> After your explanation of the usage of ObjcPtr#regard_as, I have had  
> a second look into the source code, but I would not be able to read  
> this out of the eleven pages without any explaining comments. So  
> there did you learn it?
>
>
>
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