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# instanceCallbackCmd.cpp

    //-
    // ==========================================================================
    // Copyright 1995,2006,2008 Autodesk, Inc. All rights reserved.
    //
    // Use of this software is subject to the terms of the Autodesk
    // license agreement provided at the time of installation or download,
    // or which otherwise accompanies this software in either electronic
    // or hard copy form.
    // ==========================================================================
    //+

    /*
        File: instanceCallbackCmd.cpp
        Command: "instCallbackCmd"

        Description
            class InstanceCallbackCmd
            This plugin demonstrates the functionality added to MDagMessage class.
            The new functions added allow callbacks to be added for
                1) Instance Added for a specified node(and its instances)
                2) Instance Removed for a specified node(and its instances)
                3) Instance Added for any node
                4) Instance Removed for any node

          This plugin:
          i.   Draws a circle,
          ii.  Gets its dagPath using an iterator
          iii. Adds callback for instance added and removed for this circle.

            The callback functions just displays a message indicating the
            invocation of the registered callback function.

    */

    #include <maya/MFnPlugin.h>
    #include <maya/MPxCommand.h>
    #include <maya/MArgList.h>
    #include <maya/MItDependencyNodes.h>
    #include <maya/MFnDependencyNode.h>
    #include <maya/MString.h>
    #include <maya/MGlobal.h>
    #include <maya/MLockMessage.h>
    #include <maya/MFnAttribute.h>
    #include <maya/MFnMesh.h>
    #include <maya/MFloatPointArray.h>
    #include <maya/MIntArray.h>
    #include <maya/MDagPath.h>
    #include <maya/MDagMessage.h>
    #include <maya/MFnNurbsCurve.h>

    // callback function for instance added
    void addCallbackFunc (MDagPath &dagPath, MDagPath &otherPath,
            void *clientData/*, MLockMessage::LockDAGEvent eventType, bool &decision*/ )
    {
        MGlobal::displayInfo("CALLBACK-FUNCTION REGISTERED FOR INSTANCE ADDED INVOKED");
    }

    // callback function for instance removed
    void remCallbackFunc ( MDagPath &dagPath, MDagPath &otherPath, void *clientData)
    {
        MGlobal::displayInfo("CALLBACK-FUNCTION REGISTERED FOR INSTANCE REMOVED INVOKED");
    }

    class InstanceCallbackCmd : public MPxCommand
    {

    public:

        MStatus doIt( const MArgList& args );
        static void* creator();
    };

    void* InstanceCallbackCmd::creator()
    {
        return new InstanceCallbackCmd;
    }

    MStatus InstanceCallbackCmd::doIt( const MArgList& args )
    {

        MStatus status = MS::kSuccess;

        // Draw a circle and get its dagPath
        // using an iterator
        MGlobal::executeCommand("circle");
        MFnNurbsCurve circle;

        MDagPath dagPath;
        MItDependencyNodes iter( MFn::kNurbsCurve , &status);

        for(iter.reset(); !iter.isDone() ; iter.next())
        {
            MObject item = iter.item();
            if(item.hasFn(MFn::kNurbsCurve))
            {
                circle.setObject(item);
                circle.getPath(dagPath);
                MGlobal::displayInfo("DAG_PATH is " + dagPath.fullPathName());

                if(dagPath.isValid())
                {
                    // register callback for instance add AND remove
                    //
                    MDagMessage::addInstanceAddedCallback   ( dagPath,addCallbackFunc,  NULL, &status);
                    MDagMessage::addInstanceRemovedCallback ( dagPath,remCallbackFunc,  NULL, &status);

                    MGlobal::displayInfo("CALLBACK ADDED FOR INSTANCE ADD/REMOVE");

                }

            }
        }

        if (status != MS::kSuccess)
        {
            MGlobal::displayInfo("STATUS RETURNED IS NOT SUCCESS");
        }

        return status;
    }

    //
    //              Init // UnInit
    //
    MStatus initializePlugin( MObject obj )
    {
        MStatus   status;
        MFnPlugin plugin( obj, PLUGIN_COMPANY, "6.0", "Any");
        plugin.registerCommand( "instCallbackCmd", InstanceCallbackCmd::creator);
        MGlobal::displayInfo("PLUGIN LOADED");
        return status;
    }

    MStatus uninitializePlugin( MObject obj )
    {
        MStatus   status;
        MFnPlugin plugin( obj );
        plugin.deregisterCommand( "instCallbackCmd" );
        return status;
    }