public CCNode getChildByTag(string tag)
{
NSUtils.Assert(tag!=null, "tag is null.");
if(_children!=null){
var enumerator = _children.GetEnumerator();
while (enumerator.MoveNext()) {
CCNode node = enumerator.Current;
if(node.userTag == tag){
return node;
}
}
}
// not found
return null;
}
/* "add" logic MUST only be on this method