Hi, I writing a node for Maya, and actually I encountor a strange problem,getting values from MFnCompoundAttribute in compute() function, please see this tester code, when I want to use it in Maya for example connect output to a transform object, when i change parameters the transform move strange, I did whatever you thing, but I still have problem, I would be so appreciated if you help me?
Thank you.

#pragma once
#include <maya/MPxNode.h>
#include <maya/MFnNumericAttribute.h>
#include <maya/MFnGenericAttribute.h>
#include <maya/MFnTypedAttribute.h>
#include <maya/MFnCompoundAttribute.h>
#include <maya/MVector.h>
#include <maya/MFnDependencyNode.h>
#include <maya/MTypeId.h>

//---------------------------------------------------------------------------
// Test Node class
//---------------------------------------------------------------------------
class TestNode : public MPxNode
{
public:
TestNode();
virtual ~TestNode();

virtual MStatus compute( const MPlug& plug, MDataBlock& data );

static void* creator();
static MStatus initialize();

public:

static MObject input1;
static MObject input2;
static MObject input3;
static MObject output;
static MObject compTrgt;

static MTypeId id;
};

#include <maya/MPlug.h>
#include <maya/MDataBlock.h>
#include <maya/MDataHandle.h>
#include <maya/MGlobal.h>

//
#include “TestNode.h”

// Static members
MTypeId TestNode::id( 0x81c00 ); //something for test
MObject TestNode::input1;
MObject TestNode::input2;
MObject TestNode::input3;
MObject TestNode::output;
MObject TestNode::compTrgt;
//-------------------------------------------------------

TestNode::TestNode()
{
}
TestNode::~TestNode()
{
}
//---------------------------------------------------------------------------
//
//
//---------------------------------------------------------------------------
void* TestNode::creator()
{
return new TestNode();
}

//---------------------------------------------------------------------------
// Initialize()
//
//---------------------------------------------------------------------------
MStatus TestNode::initialize()
{
MStatus stat;
MFnNumericAttribute nAttr;

input1 = nAttr.createPoint( “input1”, “in1” );
nAttr.setKeyable(true);

input2 = nAttr.createPoint( “input2”, “in2” );
nAttr.setKeyable(true);

input3 = nAttr.createPoint( “input3”, “in3");
nAttr.setKeyable(true);

//------------------
MFnCompoundAttribute compAttr;
compTrgt = compAttr.create("compTrgt", “ctgt");

compAttr.addChild(input1);
compAttr.addChild(input2);
compAttr.addChild(input3);
compAttr.setArray(true);
//compAttr.setUsesArrayDataBuilder(true);

//compAttr.setIndexMatters(true);

// Output
output = nAttr.createPoint( “output”, “out” );
nAttr.setReadable(true);
nAttr.setWritable(false);
nAttr.setStorable(false);

// Add the attributes we have created to the node
stat = addAttribute( compTrgt );
if (!stat) { stat.perror("addAttribute"); return stat;}

stat = addAttribute( output );
if (!stat) { stat.perror("addAttribute"); return stat;}

//Connect effect
/*
stat = attributeAffects( input3, output );
if (!stat) { stat.perror("attributeAffects"); return stat;}
*/
stat = attributeAffects( compTrgt, output );
if (!stat) { stat.perror("attributeAffects"); return stat;}

return MS::kSuccess;

}
//---------------------------------------------------------------------------
// Compute()
//---------------------------------------------------------------------------
MStatus TestNode::compute( const MPlug& plug, MDataBlock& data )

{
MStatus returnStatus;

if( plug ==TestNode::output )
{
MVector result;

//MObject currNode = thisMObject();
//MPlug plugin1( currNode, input1);
//MPlug plugin2( currNode, input2);
//MPlug plugin3( currNode, input3);

MArrayDataHandle inputArrayData = data.inputArrayValue( compTrgt, &returnStatus );

if( returnStatus != MS::kSuccess )
MGlobal::displayError( “Node TestNode cannot get value\n” );

else
{
unsigned int i, count = inputArrayData.elementCount();
for(i =0; i < count; i++)
{
//inputArrayData.jumpToArrayElement(i);
MVector in1, in2, in3;
//
MDataHandle currElementHandle = inputArrayData.inputValue( &returnStatus );

//
in1 = currElementHandle.child(input1).asVector();
//MGlobal::displayInfo( MString("in1.x = “) + in1.x + MString(” in1.y = “) + in1.y + MString(” in1.z = “) + in1.z );
in2 = currElementHandle.child(input2).asVector();
//MGlobal::displayInfo( MString("in2.x = “) + in2.x + MString(” in2.y = “) + in2.y + MString(” in2.z = “) + in2.z );
in3 = currElementHandle.child(input3).asVector();
//MGlobal::displayInfo( MString("in3.x = “) + in3.x + MString(” in3.y = “) + in3.y + MString(” in3.z = “) + in3.z );

result += in1 + in2+ in3;

//=======================
//if( !inputArrayData.next()) break;
//inputArrayData.setAllClean();
inputArrayData.next();
}

//Set out vector
MDataHandle outputHandle = data.outputValue( TestNode::output );
outputHandle.setMVector( result );

//clean
data.setClean(plug);
outputHandle.setClean();

}// end else

}
else
return MS::kUnknownParameter;

return MS::kSuccess;
}
//---------------------------------------------------------------------------

didn’t see where you do addAttribute() on input1, input2, input3. Maybe that’s causing problems

first of all: no, you didn’t addAttribute for the child plugs. You only called addAttribute() on compTrgt and output. If you look carefully at Maya examples, you need to call addAttribute() on input1, input2 and input3. One indicator you are doing something funny is when I unload the plugin with the code you provided, Maya crashed.

secondly: I think the odd result you get is related to createPoint().
If you use
input1 = nAttr.create("input1”,"in1", MFnNumericData::k3Double, 0, &status);
input2 = nAttr.create("input2”,"in2", MFnNumericData::k3Double, 0, &status);
input3 = nAttr.create("input3”,"in3", MFnNumericData::k3Double, 0, &status);
output = nAttr.create("output”,"out", MFnNumericData::k3Double, 0, &status);
you should be able to get the correct result. The attribute “translate” on a transform node is of type double3, so I do believe this is the more appropriate type to create. I’ve never used createPoint() so I can only guess between MPoint, MVector and double3 one of the conversions is wrong and thus causing the weird result.