public void GetChildrenFor( string promptName, string parameterName, ITreeNode treeNode, Action <ObservableCollection <ITreeNode> > result) { _childPromptLevelService.GetChildrenAsync( promptName , parameterName , treeNode.GetParameterValueHierarchy() , r => OnGetChildrenCompleted(r, promptName, treeNode, result) , OnGetChildrenError); }