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179

Creating a New Generalized Operation

The UndoOperation method could also have been implemented without the use of 
the values stored in the command set object simply by decrementing the value of 
the STYLE property for each target. 

The operation class RedoOperation method is called when the user redoes the 
operation by selecting “Redo” from a menu or toolbar.

The following example code shows a very simple RedoOperation method for the 

ExampleOp

 operation:

FUNCTION ExampleOp::RedoOperation, oCommandSet

; Retrieve the IDLitCommand objects stored in the

; command set object.

oCmds = oCommandSet->Get(/ALL, COUNT = nObjs)

; Get a reference to the iTool object.

oTool = self->GetTool()

; Loop through the IDLitCommand objects and restore the

; new values.

FOR i = 0, nObjs-1 DO BEGIN

oCmds[i]->GetProperty, TARGET_IDENTIFIER = idTarget

oTarget = oTool->GetByIdentifier(idTarget)

; Get the new value

IF (oCmds[i]->GetItem('NEW_STYLE', styleIndex) EQ 1) THEN $

oTarget->SetProperty, STYLE = styleIndex

ENDFOR

RETURN, 1

END

The RedoOperation method does the following things:

1. Retrieves an array of IDLitCommand objects from the supplied 

IDLitCommandSet object

2. Gets a reference to the iTool object.