ITT Rule IDL Version 7.0 User Manual download pdf (Page 146)

146 Chapter 7: Creating an Operation

Overview of Creating an iTool Operation iTool Developer’s Guide

Overview of Creating an iTool Operation

An operation is an iTool component object class that can be used to modify selected

data, change the way a visualization is displayed in the iTool window, or otherwise

affect the state of the iTool. Some examples of iTool operations are:

• performing the IDL SMOOTH operation on selected data,

• rotating a selected visualization by a specified angle,

• displaying data statistics.

A number of standard operations are predefined and included in the IDL iTools

package; if none of the predefined operations suits your needs, you can create your

own operation by subclassing either from the base IDLitOperation class on which all

of the predefined operations are based, from the IDLitDataOperation class, or from

one of the predefined operations.

The Operation Creation Process

To create a new iTool operation, you will do the following:

• Choose an iTool operation class on which your new operation will be based. In

most cases, the operation will act on the data underlying a visualization; in

these cases, you will base your new operation on the IDLitDataOperation

class. If your operation will affect something other than data — the appearance

of visualizations in the iTool window, or the value of some property — you

will base your new class on the IDLitOperation class. Both classes provide

support for the iTool undo/redo system, but operations that do not deal directly

with data require additional code to properly allow for undoing and redoing the

operations.

• Define the properties of the operation, and set default property values.

• If the new operation acts directly on data (that is, if it is based on the

IDLitDataOperation class), provide an Execute method that performs the

operation using the current property values. Similarly, if the new operation is

more general and is based on the IDLitOperation class, provide a DoAction

method.

• Optionally provide a DoExecuteUI method to display a user interface for

operations that act directly on data.

• For generalized operations, provide UndoOperation and RedoOperation

methods to undo and redo the operation. These methods may in turn require

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ITT Rule IDL Version 7.0 User Manual Page 146