ITT Rule IDL Version 7.0 Bedienungsanleitung PDF herunterladen (Seite 164)

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164 Chapter 7: Creating an Operation

Creating a New Data-Centric Operation iTool Developer’s Guide

Creating an UndoExecute Method

The operation class’ UndoExecute method is called when the user undoes an

invocation of the operation and the REVERSIBLE_OPERATION property is set on

the operation object. (See “Operations and the Undo/Redo System” on page 150 for

details on how undo and redo are handled in different situations.) The UndoExecute

method must reverse the effect of the Execute method.

The actual processing performed by the UndoExecute method depends entirely on

the operation.

Example UndoExecute Method

The following example code shows a simple UndoExecute method for the

ExampleDataOp operation, which reverses the operation of the Execute method.

FUNCTION ExampleDataOp::UndoExecute, data

; If byte data then offsets are 0 and 255, otherwise

; use data minimum and maximum.

offsetMax = (SIZE(data, /TYPE) eq 1) ? 255b : MAX(data)

offsetMin = (SIZE(data, /TYPE) eq 1) ? 0b : MIN(data)

data = offsetMax - TEMPORARY(data) + offsetMin

RETURN, 1

END

Discussion

When the user undoes an invocation of our ExampleDataOp operation, the iTool

system supplies the data that were computed by the Execute method when the

operation was invoked. Our UndoExecute method then reverses the original

operation.

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