Callback not append

[Rémi Deletrain]

Hello everyone,

It's been a long time since I came here to ask questions ... :)

I have a problem again that I haven't been able to solve yet.

I have attributes of type string which are paths. I must have a callback on it to call a resolver if path change.

As long as my attribute is not connected the callback works. However, if my string attribute is connected, the value changes but the callback is not called...

Does anyone know why?

[Marcus Ottosson]

Which callback are you using? Can you post something to reproduce the problem?

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[Rémi Deletrain]

in new scene launch this code:

from maya import cmds, OpenMaya

msl = OpenMaya.MSelectionList()

def get_object(s):

    mo = OpenMaya.MObject()

    msl.clear()

    msl.add(s)

    msl.getDependNode(0, mo)

    return mo

def cb(*args, **kwargs):

    

    msg = args[0]

    plug = args[1]

    other_plug = args[2]

    print msg

    print '----- Attribute {0} Change'.format(plug.name())

s_attr = 'className'

s_node_1 = cmds.createNode('transform', name='Node1')

mo_node_1 = get_object(s_node_1)

cmds.addAttr(s_node_1, longName=s_attr, dataType='string')

s_node_2 = cmds.createNode('transform', name='Node2')

cmds.addAttr(s_node_2, longName=s_attr, dataType='string')

i_call_back_id = OpenMaya.MNodeMessage().addAttributeChangedCallback(get_object(s_node_2), cb)

cmds.connectAttr('{0}.{1}'.format(s_node_1, s_attr), '{0}.{1}'.format(s_node_2, s_attr))

If you change the value of Node1.className nothing is printed in script editor.
If you disconnect Node1.className to Node2.className and change value of attribute Node2.className I have my print of my callback.

[Justin Israel]

Looks like if you use MNodeMessage.addNodeDirtyPlugCallback() instead, it will trigger either when the attribute directly changes or when it is connected as is indirectly changed.

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[Rémi Deletrain]

thanks for your reply Justin.

Indeed, via this callback I enter into my function. However the plug that we gave does not yet contain the value.

So my resolver cannot process anything.

[Rémi Deletrain]

In fact I recive the value before attribute change.

[Justin Israel]

You could use the dirty callback to know that the connected plug has changed, even though it hasn't evaluated yet. And then defer actually handling its new value until after evaluation.

from maya import cmds, OpenMaya, utils

def handle_attr(attr):
    print '-- Attribute {0} Changed: {1}'.format(attr, cmds.getAttr(attr))

def cb(msg, plug, *args, **kwargs):
    print '-- Attribute {0} Dirty'.format(plug.name())
    utils.executeDeferred(handle_attr, plug.name())

On Wed, Aug 5, 2020 at 9:40 PM Rémi Deletrain <remi.de...@gmail.com> wrote:

In fact I recive the value before attribute change.

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[Rémi Deletrain]

Thanks Justin ! Your solution works.

I did not know the utils module and the executeDeferred method ...

Thank you again !

[Justin Israel]

I have no explanation, but it seems that once you connect the addNodeDirtyPlugCallback, it causes the connected attribute of the second node to not update its value until the second time you set it. I've tried 2 versions of maya and it is the same behaviour.

On Wed, Aug 12, 2020 at 9:23 PM Rémi Deletrain <remi.de...@gmail.com> wrote:

Hi !

I reiterate because in fact the problem is not completely resolved.

```

from maya import cmds, OpenMaya, utils

def qd_handle_attr_cb(mp):

    print mp.adString()

def qd_dirty_plug_cb(mo, mp, *args, **kwargs):

    if OpenMaya.MFnAttribute(mp.attribute()).name() != 'fileName':

        return

    print mp.adString()

    utils.executeDeferred(qd_handle_attr_cb, OpenMaya.MPlug(mp.node(), mp.attribute()))

cmds.addExtension(nodeType='transform', longName='fileName', dataType='string')

s_node_1 = cmds.createNode('transform')

s_node_2 = cmds.createNode('transform')

cmds.connectAttr('{0}.fileName'.format(s_node_1), '{0}.fileName'.format(s_node_2))

msl = OpenMaya.MSelectionList()

msl.add(s_node_2)

mo = OpenMaya.MObject()

msl.getDependNode(0, mo)

i_call_back = OpenMaya.MNodeMessage.addNodeDirtyPlugCallback(mo, qd_dirty_plug_cb)

# OpenMaya.MNodeMessage.removeCallback(i_call_back)

```

If I set s_node_1.fileName my callback is append but the value setted on s_node_2.fileName is not valid. The attribute s_node_2.fileName has a delay value.
You have solution for this case ?

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[Rémi Deletrain]

Ok thanks for your test Justin !

It's possible top considerate that a bug of attribute string ?