| Re: How to do nested objects?? [message #35519] |
Wed, 25 June 2003 05:38  |
btt
Messages: 345
Registered: December 2000
|
Senior Member |
|
|
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
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
