MDataHandle.setFloat() isn't changing Plug value

Question

Using the Maya Python API 2.0, I'm trying to make a callback that changes the value of a plug. However, none of the methods I've tried are working.

I've tried using the MPlug.setFloat() method, but this didn't lead to expected results; I found no change in the plug's value. I figured this hadn't worked because I needed to clean the plug after changing its value. So, I then tried getting the plug's data handle using the MPlug.asDataHandle() method, then using the data handle's datablock() method in order to use the data handle and datablock to set the plug's value and clean it. However, I got an error saying "RuntimeError: (kFailure): Unexpected Internal Failure" upon using MDataHandle.datablock().

Now I'm trying the following, which uses the data handle to set the plug's value and clean it:

def setPlugFloatValue(node, plugName, val):
    fnSet = OpenMaya.MFnDependencyNode(node)
    plug = fnSet.findPlug(plugName,True)
    handle = plug.asMDataHandle()
    handle.setFloat(val)
    handle.setClean()

The above function is intended to find a certain plug in a node, then use its data handle to set its value and clean it. In my program, the callback uses this function to change the translateX, translateY and translateZ plugs of a node's child nodes. The callback runs when the translate value of the node it's applied to changes. In a scene I'm using to test this callback, I apply the callback to a polygon mesh object, with one child which is also a polygon mesh object. So, as I translate the parent object, I expect the translate values of its child to change. But when I select the child object after translating its parent, its translate values haven't changed.

score 0 · Answer 1 · answered Apr 17 '19 at 13:41

Tried your example and used setFloat() on the plug, which appears to work fine.

import maya.api.OpenMaya as OpenMaya

def setPlugFloatValue(node, plugName, val):
    fnSet = OpenMaya.MFnDependencyNode(node)
    plug = fnSet.findPlug(plugName,True)
    plug.setFloat(val)

def applyToSelectedObjects():
    sl_list = OpenMaya.MGlobal.getActiveSelectionList()
    iterator = OpenMaya.MItSelectionList(sl_list)

    while not iterator.isDone():
        obj = iterator.getDependNode()
        setPlugFloatValue(obj, "translateX", -2.0)
        iterator.next()

applyToSelectedObjects()

Perhaps your issue is something else? You can also try to use setMDistance() instead, but it didn't make any difference in my testing.

distance = OpenMaya.MDistance(val)
plug.setMDistance(distance)

MDataHandle.setFloat() isn't changing Plug value

1 Answers1