How To Set The Visibility Attribute Of An Object

[yunjun]

instead of using MGlobal::executeCommand (MString( "setAttr ") + ....+".visibility " + 1/0), is there any other way to set the visibility attribute of an object?

[daniel-faust]

You could use the MPlug::setValue() method, but you'd have to implement undo / redo by yourself.

[yunjun]

thanks a lot. when you say undo/redo, do you mean I have to remember the previous visibility value and use the MPlug::setValue (to set it back) again to in undo?

I also don't know how to construct the MPlug, it seems I can use
MPlug ( const MObject & node , const MObject & attribute )

I can get the node from MObject obj = dagPath.node(), but how can I get the attribute?

[daniel-faust]

Yes, you first use MPlug::getValue to get the current value, store it in a member variable, then set the value of the plug with MPlug::setValue().

Should you later encounter that MGlobal::isUndo (cant remember if thats the name) or MGlobal::isRedo is valid, then you need to undo your chanve by doing a setValue() with the value you stored in the member variable, or redo with your the value with which you initially changed the plug, respectively. A lot of work for such a small piece of s... Your mel command you issue with MGlobal::executeCommand handles undo/redo automatically if you set the undoable parameter to true. Nice!

The second parameter in the MPlug is the name of the attribute. remember those attributes are static members, so their location is known in memory so that Maya knows which attribtue is meant. It can look like MPxLocator::worldPositionX:

MPlug myWorldX(myLocatorNode.thisMObject(), MPxLocator::worldPositionX).

---

If you deal with non-custom nodes, the easiest way to get the MPlug is to use the findPlug("attributeName)

MPlug findPlug ( const MObject & attr, bool wantNetworkedPlug, MStatus * ReturnStatus=NULL) const

which is offered by MFnDependencyNode: and its descendants, as well as by the MDagPath I believe.

[yunjun]

thank you, Daniel_Faust.
I guess it is a better idea to stay with the MGlobal::executeCommand for me at the moment. Using the MPlug for just setting the visibility is possibly going to take me too much time.
Two more questions, if I use the MGlobal::executeCommand in my doIt(), are my redoIt() and undoIt() just going to be empty like:

CODE
MStatus    SetVisibilityCmd::redoIt()
{    
    return MS::kSuccess;    
}

MStatus    SetVisibilityCmd::undoIt()
{    
    return MS::kSuccess;
}

It seems to be working, but just looks too simple to be true.

Also, I want to know, to execute a Mel command, when to use the MDGModifier::commandToExecute and when to use the MGlobal::executeCommand.

Appreciate your help!

[daniel-faust]

Ok, you should leave them empty.

But, now that you mention the MDGModifier::commandToExecute(), this is also a possibility.

You'd create a member variable of type MDGModifier in your MPxCommand class.

class MPxMyCommand :: MPxMyCommand {
MDGModifier mod;
doIt()
undoIt()
redoIt()
}

During your doIt() you execute
mod.commandToExecute(...);
mod.doIt();

During your undoIt() you execute
mod.undoIt();

During your redoIt() you execute
mod.redoIt();

---

That's a really clean implementation, quite easy. You'll be dealing a lot with MDGModifier when you create/delete nodes and/or create/destroy connections from within your plug-in, so you might want to use it now to use it a bit.

Without mel it would look like
class MPxMyCommand :: MPxMyCommand {
bool newVis;
bool oldVis;
doIt()
undoIt()
redoIt()
}

During your doIt() you execute
newVis = newValueFromArg; // store new value
plug.getValue(oldVis) // store original value
plug.setValue(newVis)

During your undoIt() you execute
plug.setValue(oldVis)

During your redoIt() you execute
plug.setValue(newVis)

[yunjun]

Thanks a lot!
I checked the MDGModifier, and it seems there is no redoIt(). Most of the examples I saw are like this:

class MPxMyCommand :: MPxMyCommand {
MDGModifier mod;
doIt()
undoIt()
}

During doIt()
mod.commandToExecute(...);
return redoIt();

During undoIt()
mod.undoIt();

During redoIt()
mod.doIt();

I tried the above code and the undo/redo worked!

[daniel-faust]

Oh, right, I missed that, sorry. Using doIt to redo is the correct way.