user manual

Chapter 8: Creating a Manipulator 205
iTool Developer’s Guide Using Manipulator Public Instance Data
Using the nSelectionList Field
The nSelectionList field contains the number of currently selected items in the
window associated with the current manipulator. This corresponds to the number of
visualizations contained within the
pSelectionList pointer, described in the
following section. If no visualizations have been selected, the
nSelectionList
value equals 0 and the
pSelectionList will contain an undefined IDL variable.
The
nSelectionList can be used to ensure the user has made a selection. For
example, in an OnMouseDown method, you may use a statement similar to the
following to ensure a selection has been made:
; If nothing selected we are done.
IF (self.nSelectionList EQ 0) THEN $
RETURN
The nSelectionList field value can also be used to loop through the collection of
selected visualizations as shown in the following section.
Using the pSelectionList Pointer Field
The pSelectionList field is a pointer to an array of visualizations currently
selected in the window. Use the
nSelectionList value to cycle through this array.
If a manipulator only acts upon visualizations of a certain type you can verify the
type of each selected item in
pSelectionList before attempting to modify the
visualization. The
nSelectionList and pSelectionList public instance data
fields are available from any manipulator object’s predefined or custom methods.
; Loop through all selected visualizations.
FOR i=0, self.nSelectionList-1 DO BEGIN
oVis = (*self.pSelectionList)[i]
; Verify type of visualization or manipulate it.
; ...
ENDFOR
Note
The
pSelectionList field is a pointer. You must use IDL pointer syntax to
access items in the field.
See “Example: Color Table Manipulator” on page 226 for a complete example that
uses these public instance data fields.