[MacRuby-devel] Understanding Pointer objects

[Mark Rada]

On 2010-10-24, at 9:34 PM, Laurent Sansonetti wrote:

> Hi Mark,
> 
> Matt already replied but I thought I would give more info.
> 
> On Oct 23, 2010, at 10:04 PM, Mark Rada wrote:
> 
>> Hi,
>> 
>> I've been trying to play with using the Accessibility API to do some automated testing.
>> 
>>> From what I have researched, I have to use some C functions that often need a reference passed to the them. 
>> 
>> I am at a loss when trying to deal with Pointer objects. I've tried playing with them and googling it, but I just cannot figure out how to turn a pointer into a more useful type or to get what I want out of them.
>> 
>> For example, I can start like this:
>> 
>> 	framework 'Cocoa'
>> 
>> 	unless AXAPIEnabled() # only works if I include the parenthesis
>> 		puts 'Please enable Access for Assistive Devices first'
>> 		exit 2
>> 	end
> 
> That's expected, in Ruby methods starting with a capital letter must be called with explicit parentheses, otherwise they are interpreted as constants.

Ah, that makes more sense now.

> 
>> 	mail              = NSRunningApplication.runningApplicationsWithBundleIdentifier('com.apple.Mail').first
>> 	mail_object = AXUIElementCreateApplication mail.processIdentifier 
>> 
>> 	names = Pointer.new :object
>> 
>> 	AXUIElementCopyAttributeNames mail_object, names
>> 
>> 
>> But then how do I get the values out of the names pointer? For reference, I found the functions in AXUIElement.h.
> 
> 
> It looks like AXUIElementCopyAttributeNames returns a CFArray by reference. So your pointer object is properly created, to retrieve the array after the call you just use
> 
>   array = names[0]
> 
> Then, it should behave like a normal Ruby array.

Ah, that does work, and seems to have worked for a number of other things I am trying to do. 

The only problem now is when I have something like

	value = Pointer.new '^v' # pointer to pointer to void
	AXUIElementCopyAttributeValue mail_object, 'AXHidden', value

In this case I am using it right now, it will be returning a boolean, but when I try to dereference it like

	puts value[0][0] # => 120

it gives me a Fixnum, and then I can keep trying things like 

	puts value[0][1] # => 104
	puts value[0][10000] # => 0

And I seem to get nowhere.

Is there a way to cast the data back into the type I want it to be? Or am I doing something dumb?

Thanks,
	Mark


> 
> Laurent
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