Chkbox Controls in a DataGrid Header

Below I have ChkBoxes in a datagrid and it can pull the items out with the DataGridItem collection. But how do I get the value a check box in the HEADER of a data grid. I tried the DataGridColumns collection but not to much success. foreach (DataGridItem dataGridItem in dgProject.Items) { bool chkHello = ((CheckBox)dataGridItem.FindControl("chkHello")).Checked; bool chkBye = ((CheckBox)dataGridItem.FindControl("chkBye")).Checked; if (chkHello) {myArray.Add( new myArrayItem(dataGridItem.Cells{2].Text , "Hello"));} if (chkBye) {myArray.Add( new myArrayItem(dataGridItem.Cells{2].Text , "Bye"));}