python/api1/py1ParentAddedMsgCmd.py

#-
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#+

########################################################################
# DESCRIPTION:
#
# Produces the Python command "spParentAddedMsg".  
#
# This plug-in demonstrates how to create and handle messages in Python.
# A global "parent added" message along with user defined client data is created.
# Invoking an operation in Maya such as creating a polygon plane will invoke the callback.
#
# To use, you can execute the following:
#
#   import maya.cmds as cmds
#   cmds.loadPlugin("parentAddedMsgCmd.py")   
#   cmds.spParentAddedMsg()
#   cmds.polyPlane()
#
########################################################################

import sys
import maya.OpenMaya as OpenMaya
import maya.OpenMayaMPx as OpenMayaMPx

kPluginCmdName = "spParentAddedMsg"

messageId = 0
messageIdSet = False

def removeCallback(id):
    try:
        OpenMaya.MMessage.removeCallback( id )
    except:
        sys.stderr.write( "Failed to remove callback\n" )
        raise

def dagParentAddedCallback( child, parent, clientData ):
    print("dagParentAddedCallback...")
    print("\tchild %s" % child.fullPathName())
    print("\tparent %s" % parent.fullPathName())
    print("\tclient data %s" % clientData)

def createParentAddedCallback(stringData):
    # global declares module level variables that will be assigned
    global messageIdSet
    try:
        id = OpenMaya.MDagMessage.addParentAddedCallback( dagParentAddedCallback, stringData )
    except:
        sys.stderr.write( "Failed to install dag parent added callback\n" )
        messageIdSet = False
    else:
        messageIdSet = True
    return id

# command
class scriptedCommand(OpenMayaMPx.MPxCommand):
    def __init__(self):
        OpenMayaMPx.MPxCommand.__init__(self)
    def doIt(self,argList):
        global messageId
        if ( messageIdSet ):
            print("Message callaback already installed")
        else:
            print("Installing parent added callback message")
            messageId = createParentAddedCallback( "_noData_" )

# Creator
def cmdCreator():
    return OpenMayaMPx.asMPxPtr( scriptedCommand() )
    
# Initialize the script plug-in
def initializePlugin(mobject):
    mplugin = OpenMayaMPx.MFnPlugin(mobject)
    try:
        mplugin.registerCommand( kPluginCmdName, cmdCreator )
    except:
        sys.stderr.write( "Failed to register command: %s\n" % name )
        raise

# Uninitialize the script plug-in
def uninitializePlugin(mobject):
    # Remove the callback
    if ( messageIdSet ):
        removeCallback( messageId )
    # Remove the plug-in command
    mplugin = OpenMayaMPx.MFnPlugin(mobject)
    try:
        mplugin.deregisterCommand( kPluginCmdName )
    except:
        sys.stderr.write( "Failed to unregister command: %s\n" % kPluginCmdName )
        raise