private List<Project> GetDataRowHandles()
        {
            List<Project> rowHandles = new List<Project>();
            for (int i = 0; i < this.gcProject.VisibleRowCount; i++)
            {
                int rowHandle = this.gcProject.GetRowHandleByVisibleIndex(i);
                var item = this.gcProject.GetRow(rowHandle) as Project;
                if (this.gcProject.IsGroupRowHandle(rowHandle))
                {
                    if (!this.gcProject.IsGroupRowExpanded(rowHandle))
                    {
                        rowHandles.AddRange(GetDataRowHandlesInGroup(rowHandle));
                    }
                }
                else
                    rowHandles.Add(item);
            }
            return rowHandles;
        }

        private List<Project> GetDataRowHandlesInGroup(int groupRowHandle)
        {
            List<Project> rowHandles = new List<Project>();
            for (int i = 0; i < this.gcProject.GetChildRowCount(groupRowHandle); i++)
                {
                    int rowHandle = this.gcProject.GetChildRowHandle(groupRowHandle, i);

                    //Так понимаю, что здесь я неправильно получаю объект в группе
                    var item = this.gcProject.GetGroupRowValue(i) as Project;

                    if (this.gcProject.IsGroupRowHandle(rowHandle))
                    {
                    rowHandles.AddRange(GetDataRowHandlesInGroup(rowHandle));
                }
                else
                    rowHandles.Add(item);
            }
            return rowHandles;
        }

private List<int> GetDataRowHandles() {
    List<int> rowHandles = new List<int>();
    for (int i = 0; i < grid.VisibleRowCount; i++) {
        int rowHandle = grid.GetRowHandleByVisibleIndex(i);
        if (grid.IsGroupRowHandle(rowHandle)) {
            if (!grid.IsGroupRowExpanded(rowHandle)) {
                rowHandles.AddRange(GetDataRowHandlesInGroup(rowHandle));
            }
        }
        else
            rowHandles.Add(rowHandle);
    }
    return rowHandles;
}
private List<int> GetDataRowHandlesInGroup(int groupRowHandle) {
    List<int> rowHandles = new List<int>();
    for (int i = 0; i < grid.GetChildRowCount(groupRowHandle); i++) {
        int rowHandle = grid.GetChildRowHandle(groupRowHandle, i);
        if (grid.IsGroupRowHandle(rowHandle)) {
            rowHandles.AddRange(GetDataRowHandlesInGroup(rowHandle));
        }
        else
            rowHandles.Add(rowHandle);
    }
    return rowHandles;
}