| Re: How to do nested objects?? [message #35519] |
Wed, 25 June 2003 05:38 |
btt
Messages: 345
Registered: December 2000
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Senior Member |
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Mark Hadfield wrote:
> "Jon Robinson" <wonjrobinson@erols.com> wrote in message
> news:bdam9s$ati$1@bob.news.rcn.net...
>
>
>> I have a class that I want to have hold another object. My code
>> compiles without error, however, when I try to run it, I get the
>> error:
<snip>
>
> In the __define routine for the containing object, use obj_new()
> instead of the name of the contained object.
>
> PRO JWR_CalibrationNotes__define
> struct = { JWR_CalibrationNotes, InFileName:'', $
> PathToDataFiles:'', $
> NumberOfNotes:0, $
> NotesArray:OBJARR(80), $
> CalibImageFileNames:obj_new(), ROIFileIDs:LONARR(4) }
> END ; PRO JWR_CalibrationNotes__define
>
> Then in the Init routine for the containing object, you must created
> the contained object and store a reference in the appropriate field of
> your class structure
>
> function JWR_CalibrationNotes::Init
> self.CalibImageFileNames = obj_new('JWR_CAL_Image_File_Names')
> ;; Do other initialisation stuff
> return, 1
> end
>
> You'll almost certainly want to destroy the contained object in the Cleanup
> method also.
>
> The thing to remember is that a __define procedure for a class
> structure (or for a named structure) only *defines* the structure. It
> does this by creating a prototype instance of the structure, then
> discarding it when the procedure terminates. The next time an object
> of the same class (or named structure of the same type) is created, it
> has the same fields and data types as the prototype, but none of the
> actual data.
>
Hi,
Just to add a bit to Mark's nice description. The values in the newly
created and 'unpopulated' prototype are all set to 0 for numeric values,
empty-string for strings, null-pointer for pointers and null-objects for
objects.
Cheers,
Ben
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| Re: How to do nested objects?? [message #35524 is a reply to message #35519] |
Tue, 24 June 2003 16:43  |
Mark Hadfield
Messages: 783
Registered: May 1995
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Senior Member |
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"Jon Robinson" <wonjrobinson@erols.com> wrote in message
news:bdam9s$ati$1@bob.news.rcn.net...
>
> I have a class that I want to have hold another object. My code
> compiles without error, however, when I try to run it, I get the
> error:
>
> % Variable is undefined: JWR_CAL_IMAGE_FILE_NAMES.
> % Execution halted at: JWR_CALIBRATIONNOTES__DEFINE 196
>
C:\RSI\IDL56\products\envi36\save_add\MultiSpectralImageCali bration__define.
> pro
> % OBJ_NEW
> % MULTISPECTRALCALIBRATION 13
> C:\RSI\IDL56\products\envi36\save_add\MultiSpectralCalibrati on.pro
> % $MAIN$
>
> The contained object is:
>
> PRO JWR_CAL_Image_File_Names__define
> struct = { JWR_CAL_Image_File_Names, InFileNames:STRARR(251) }
> END ; PRO JWR_CAL_Image_File_Names__define
>
> The containing object is:
>
> PRO JWR_CalibrationNotes__define
> struct = { JWR_CalibrationNotes, InFileName:'', $
> PathToDataFiles:'', $
> NumberOfNotes:0, $
> NotesArray:OBJARR(80), $
> CalibImageFileNames:JWR_CAL_Image_File_Names, ROIFileIDs:LONARR(4) }
> END ; PRO JWR_CalibrationNotes__define
>
> I get the error message quoted above when I try to create the
> containing object:
In the __define routine for the containing object, use obj_new()
instead of the name of the contained object.
PRO JWR_CalibrationNotes__define
struct = { JWR_CalibrationNotes, InFileName:'', $
PathToDataFiles:'', $
NumberOfNotes:0, $
NotesArray:OBJARR(80), $
CalibImageFileNames:obj_new(), ROIFileIDs:LONARR(4) }
END ; PRO JWR_CalibrationNotes__define
Then in the Init routine for the containing object, you must created
the contained object and store a reference in the appropriate field of
your class structure
function JWR_CalibrationNotes::Init
self.CalibImageFileNames = obj_new('JWR_CAL_Image_File_Names')
;; Do other initialisation stuff
return, 1
end
You'll almost certainly want to destroy the contained object in the Cleanup
method also.
The thing to remember is that a __define procedure for a class
structure (or for a named structure) only *defines* the structure. It
does this by creating a prototype instance of the structure, then
discarding it when the procedure terminates. The next time an object
of the same class (or named structure of the same type) is created, it
has the same fields and data types as the prototype, but none of the
actual data.
--
Mark Hadfield "Ka puwaha te tai nei, Hoea tatou"
m.hadfield@niwa.co.nz
National Institute for Water and Atmospheric Research (NIWA)
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