ITT Rule IDL Version 7.0 User Manual download pdf (Page 263)

Chapter 10: Creating a File Writer 263

iTool Developer’s Guide Creating a New File Writer

Passing Through Caller-Supplied Property Settings

If you have included the _REF_EXTRA keyword in your function definition, you can

use IDL’s keyword inheritance mechanism to pass any “extra” keyword values

included in the call to the Init method through to other routines. One of the things this

allows you to do is specify property settings when the Init method is called; simply

include each property’s keyword/value pair when calling the Init method, and include

the following in the body of the Init method:

IF (N_ELEMENTS(_extra) GT 0) THEN $

self->

MyWriter

::SetProperty, _EXTRA = _extra

where MyWriter is the name of your file writer class. This line has the effect of

passing any “extra” keyword values to your file writer class’ SetProperty method,

where they can either be handled directly or passed through to the SetProperty

methods of the superclasses of your class. See “Creating a SetProperty Method” on

page 265 for details.

Example Init Method

FUNCTION ExampleWriter::Init, _REF_EXTRA = _extra

IF (self->IDLitWriter::Init('ppm', TYPE='IDLIMAGE', $

NAME='Portable Pixmap (PPM) File', $

DESCRIPTION="PPM File Writer", $

_EXTRA = _extra) EQ 0) THEN $

RETURN, 0

RETURN, 1

END

Discussion

The

ExampleWriter class is based on the IDLitWriter class (discussed in

“Subclassing from the IDLitWriter Class” on page 258). As a result, all of the

standard features of an iTool file writer class are already present. We don’t define any

keyword values to be handled explicitly in the Init method, but we do use the

keyword inheritance mechanism to pass keyword values through to methods called

within the Init method. The

ExampleWriter Init method does the following things:

1. Calls the Init method of the superclass, IDLitWriter. We specify a list of

accepted filename extensions (only

ppm, in this case) via the Extensions

argument, and set the TYPES keyword. We include a description of the writer

via the DESCRIPTION keyword. Finally, we use the _EXTRA keyword

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ITT Rule IDL Version 7.0 User Manual Page 263