ITT Rule IDL Version 7.0 Manual do Utilizador descarregar pdf (Página 260)

260 Chapter 10: Creating a File Writer

Creating a New File Writer iTool Developer’s Guide

Definition of the Init Function

Begin by defining the argument and keyword list for your Init method. The argument

and keyword list defines positional parameters (arguments) accepted by your method,

defines any keywords that will be handled directly by your method, and specifies

whether keywords not explicitly handled by your method will be passed through to

other routines called by your method via IDL’s keyword inheritance mechanism. The

Init method for a file writer generally looks something like this:

FUNCTION

MyWriter

::Init,

MYKEYWORD1

= mykeyword1, $

MYKEYWORD2

= mykeyword2, ..., _REF_EXTRA = _extra

where MyWriter is the name of your file writer class and the MYKEYWORD

parameters are keywords handled explicitly by your Init function.

Note

Always use keyword inheritance (the _REF_EXTRA keyword) to pass keyword

parameters through to any called routines. (See “Keyword Inheritance” (Chapter 5,

Application Programming) for details on IDL’s keyword inheritance mechanism.)

Superclass Initialization

The file writer class Init method should call the Init method of any required

superclass. For example, if your file writer is based on an existing file writer class,

you would call that class’ Init method:

self->

SomeFileWriterClass

::Init(_EXTRA = _extra)

where SomeFileWriterClass is the class definition file for the file writer on which

your new file writer is based.

Note

Your file writer class may have multiple superclasses. In general, each superclass’

Init method should be invoked by your class’ Init method.

Error Checking

Rather than simply calling the superclass Init method, it is a good idea to check

whether the call to the superclass Init method succeeded. The following statement

checks the value returned by the superclass Init method; if the returned value is 0

(indicating failure), the current Init method also immediately returns with a value of

IF ( self->

SomeFileWriterClass

::Init(_EXTRA = _extra) EQ 0) THEN $

RETURN, 0

1 2 ... 255 256 257 258 259 260 261 262 263 264 265 ... 429 430

Sem comentários

ITT Rule IDL Version 7.0 Manual do Utilizador Página 260