public void MovePrevTaskCell()
{
m_tasksTreeView.GrabFocus ();
TreePath path;
TreeViewColumn column;
m_tasksTreeView.GetCursor (out path, out column);
int index = GetColumnOffset (column);
if (index - 1 < 0)
column = m_tasksTreeView.Columns[m_tasksTreeView.Columns.Length - 1];
else
column = m_tasksTreeView.Columns[index - 1];
m_tasksTreeView.SetCursor (path, column, false);
}