ITT Rule IDL Version 7.0 Manual de usuario descargar pdf (Pagina 265)

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Chapter 10: Creating a File Writer 265

iTool Developer’s Guide Creating a New File Writer

Note

Any property registered with a call to the RegisterProperty method must be listed as

a keyword to the GetProperty method either of the visualization class or one of its

superclasses.

Note

A file writer need not register any properties at all, if the write operation is simple.

Many of the standard iTool image file writers work without registering any

properties.

See “IDLitWriter::GetProperty” (IDL Reference Guide) for additional details.

Example GetProperty Method

PRO ExampleWriter::GetProperty, _REF_EXTRA = _extra

IF (N_ELEMENTS(_extra) GT 0) THEN $

self->IDLitWriter::GetProperty, _EXTRA = _extra

END

Discussion

The GetProperty method first defines the keywords it will accept. There must be a

keyword for each property of the file writer. Since the file writer we are creating has

no properties of its own, there are no keywords explicitly defined. Note the use of the

keyword inheritance mechanism to allow us to get properties from the

ExampleWriter class’ superclasses without knowing the names of the properties.

Since our

ExampleWriter class has no properties of its own, we simply call the

superclass’ GetProperty method, passing in all of the keywords stored in the

_extra

structure.

Creating a SetProperty Method

The file writer SetProperty method stores property values in the file writer object’s

instance data. It should set the specified property value, either by storing the value

directly in the visualization object’s instance data or by calling another class’

SetProperty method.

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