清除基于DataGridCheckBoxColumn检查或取消选中的数据网格单元格的内容

I have a datagrid with 2 cells. one is DataGridCheckBoxColumn and other is DataGridTextColumn. when DataGridCheckBoxColumn is unchecked i want to clear content of the DataGridTextColumn.the data is comming from database but user can edit it .please tell me how to do thisI have a datagrid with 2 cells. one is DataGrid