can't get child plug of CompoundAttribute in custom node

[568278785]

I have written a custom MPXnode that is only used to store data,

the Initialize() section of mpxnode: 

MFnCompoundAttribute compAttr;     
MFnNumericAttribute numericAttr; 

arrayCacheObj = numericAttr.create("doubleArrayC", "dAC", MFnNumericData::kDouble, 0.0);     
numericAttr.setStorable(true);     
numericAttr.setWritable(true);     
numericAttr.setKeyable(true);     
numericAttr.setReadable(true);    
 numericAttr.setArray(true); 

arrayCacheCompObj = compAttr.create("doubleArray", "dA");     
compAttr.setArray(true); 

compAttr.addChild(arrayCacheObj); 

addAttribute(arrayCacheCompObj);

 I try to get child plug in my mpxcommand and set value:

MFnDependencyNode arrayCacheNodeFn(arrayCacheNode);
MPlug dAPlug = arrayCacheNodeFn.findPlug("doubleArray", true); 

dAPlug.elementByLogicalIndex(0).elementByLogicalIndex(0).setValue(2);

did't work,what i missing?

Thanks for your help.

[jmreinhart · Accepted solution]

dAPlug.elementByLogicalIndex(0).child(0).elementByLogicalIndex(0).setValue(2);

[568278785]

Thank you,it's the answer!