Re: Is there a way to efficiently access NSArray element contents?

FROM : Jean-Daniel Dupas
DATE : Sun Jun 08 20:29:01 2008

Le 8 juin 08 à 20:13, Brent Fulgham a écrit :

> I've been enjoying the NSArray/NSMutableArray classes as I work with 
> various user interface features for a program I'm working on that 
> interacts with a legacy C++ library.
>
> I've recently begun considering how to efficiently display the 
> contents of a binary data stream.  Currently I'm appending to an 
> NSMutableArray of NSNumber objects, which is great for allowing me 
> to bind to some UI elements in close to real time and has provided a 
> simple and functional mechanism for text numerical display.
>
> Ideally, I'd like to be able to access a raw binary buffer of data 
> so I could for example bind it to something like an OpenGL vector 
> buffer for display.  However, unlike an STL vector, I don't think 
> the NS[Mutable]Array provides any guarantees of memory organization, 
> nor any way to 'unbox' the NSNumber to deal with the internal values.
>
> For example, in the STL, I could make use of the fact that the 
> vector template guarantees the storage to be in contiguous memory 
> and accessible as raw double values through the address of the first 
> element of the vector.  However, I don't think this is possible via 
> NSMutableArray and NSNumbers.
>
> Is my only option to periodically sync a buffer of binary double 
> values by copying from the NSMutableArray on some periodic basis?
>
> Thanks,
>
> -Brent


AFAK, there is no Cocoa class that fit both Cocoa Binding and raw 
stream of data. If you just need Cocoa Binding, NSArray is fine, if 
you just want a raw stream for OpenGL, you can use STL vector 
(perfectly valid using Obj-C++).
If you need both, you can probably write a small objc Vector class 
that wraps a STL vector and implements KVC compliant accessors, so you 
will be able to using with Cocoa binding, and access the raw content, 
and is just a couple of lines.

see http://developer.apple.com/documentation/Cocoa/Conceptual/KeyValueCoding/Concepts/Compliant.html
  for details about KVC methods you need.