Assuming the ControlSource is a field in a table for the column where the CheckBox is, you need to set the value of the field to the value of your Select All CheckBox.

In the INteractiveChange of the Set All CheckBox, try code like:

DODEFAULT()
local lnSelect, lcTable, lnRec
lnSelect = select()
lcTable = THISFORM.GridName.RecordSource
select (lcTable)
lnRec = RECNO()
REPLACE ALL MyField WITH THIS.VALUE
goto lnRec
select (lnSelect)

>Dear the Expert,
>I though, I met simple problem (but I cannot solve it.. I am very new with this) ;>()
>I am implementing check box in the datagrid control and there is a "Select All" check box at the footer of datagrid .. my problem is how to automatically set checked = true to all checkboxes in the datagrid when the "Select All" check box checked and how to automatically unchecked to all checkboxes when the "Select All" check box was unchecked .. .. once again sorry I am very new with this toy .. many thanks
>
>
>Best Regards,
>
>Winan