Archive for June, 2011

Maya QT interfaces in a class

Most tutorials online have suggested the way to fire commands inside QT interfaces launched in Maya (via cmds.loadUi – not involving pyQT) is to add a string property like:


Pretty craptastical – it can only fire commands inside a specific python module, the name of which has to be known when you’re laying out your interface.

Ideally, we’d like to have our interface instanced from a python class. This would allow us, amongst other things, so have multiple, independant instances. However it seems that a “self” reference can’t get passed to an interface, which is what you’d reallly like to do.


A (reasonably hacky) solution is to create the widget callbacks from inside our python class, after we’ve loaded the interface via cmds.loadUi().

import maya.cmds as cmds

class myUi(object):
	def __init__(self, *args):
		uiFile = '/path/to/uiFile.ui'
		rlDialog = cmds.loadUI(f=uiFile)
		cmds.button( "ovrAdd_btn", edit=True, command=self.overrideAdd )

	def overrideAdd(self, *args):
		print 'do something!'

Which is slightly better, but we’re still referring to our widget by a string name. This is problematic if you have multiple instances of this class – targeting “ovrAdd_btn” is going to get confusing. We need to find out exactly which control, in amongst the whole widget mess, is the one that we’ve spawned when we’re called cmds.loadUI().

Sadly, loadUI() doesn’t give us any help in this department. So, and here’s the hacky bit, we can trawl through the widgets to find those belonging to our class instance, store them in a dict and then we can refer back to them by a simplified name. Easy!

import maya.cmds as cmds

def widgetPath(windowName, widgetNames):
    @param windowName: Window instance name to search
    @param widgetNames: list of names to search for
    returnDict = {}
    mayaWidgetList = cmds.lsUI(dumpWidgets=True)
    for widget in widgetNames:
        for mayaWidge in mayaWidgetList:
            if windowName in mayaWidge:
                if mayaWidge.endswith(widget):
                    returnDict[widget] = mayaWidge
    return returnDict

class myUi(object):
	def __init__(self, *args):
		uiWidgetList = ['ovrAdd_btn']

		uiFile = '/path/to/uiFile.ui'
		rlDialog = cmds.loadUI(f=uiFile)
		self.uiObjects = widgetPath(rlDialog, uiWidgetList)
		cmds.button( self.uiObjects["ovrAdd_btn"], edit=True, command=self.overrideAdd )

	def overrideAdd(self, *args):
		print 'do something!'

Trawling through Maya’s widget list isn’t particularly elegant, but you only have to do it once per class initialisation, so there isn’t too much of a cost. The advantage is that you can now have per-instance widget names.

Why not just use pyQT proper, you ask? Installing external dependencies isn’t always an option for our less techy brethren, or easily done in a studio-wide fashion. Using pyQT would be far better (and give all sorts of other benefits), but if you’re constrained to using vanilla maya / python, this seems to do the trick.

Name changed callbacks in maya/python/api

Could not figure this out for quite a while – maya API is a little obtuse if you’re not used to it, and with all the examples in c++, you’re on your own when it comes to translating to python. Ergh.


from maya import OpenMaya

def nameChangedCallback( *args):
    node = args[0]
    # convert the MObject to a dep node
    depNode = OpenMaya.MFnDependencyNode(node)
    oldName = args[1]

    print '----\nNameChangedCallback'
    print 'newName: ',
    print 'oldName', oldName
    print 'type', depNode.typeName()


# passing in a null MObject (ie, without a name as an argument)
# registers the callback to get all name changes in the scene
# if you wanted to monitor a specific object's name changes
# you could pass a name to the MObject

nullMObject = OpenMaya.MObject()
OpenMaya.MNodeMessage.addNameChangedCallback( nullMObject, nameChangedCallback )


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