problem on assign the date value from datepicker into TAdbDBGrid

I did the same way as lookup combo, I included the following code into the GetEditorValue .. but it seems it cannot assign the date value to the grid after I selected the date from the datepicker on TAdvDBGrid. Anything get wrong ? I get stuck in this over 2 days.

procedure Tfrm_Certificate_Information.FormControlEditLink_Cert_ExpiryDateGetEditorValue(
Sender: TObject; Grid: TAdvStringGrid; var AValue: string);
begin
With DataModule_CLM_CertInfo do
begin
//Make sure the dataset is in Insert or Edit state
if (sql_Staff_Info_Details_Cert.state = dsInsert) or (sql_Staff_Info_Details_Cert.state = dsEdit) then
begin
//Assign value back from the editor to the grid's cell, otherwise once you leave the cell , the value will gone.
AValue := DateToStr(DateTimePicker_Cert_ExpiryDate.Date);
end;
end; //end With
end;

Solved.