Example 3: Reacting to a check box toggle

Uses OnCheckChange, which fires before a check box changes, to refuse a change that breaks a rule and to update a related field when the change is accepted.

Scenario

The boolean field Active is shown as a check box. A product that still has stock cannot be made inactive; when the box does change, the field UpdatedAt records the moment.

Units

Besides EgFireGrid: System.SysUtils (SameText, Abort, Now), FMX.DialogService (TDialogService) and the unit of the dataset component (here FireDAC.Comp.Client, for Query1).

The handler

procedure TForm1.Grid1CheckChange(Sender: TObject; Column: TEgFireGridColumn; RowIndex: Integer);
var
  WasActive: Boolean;
begin
  if not SameText(Column.FieldName, 'Active') then
    Exit;
  WasActive := Query1.FieldByName('Active').AsBoolean;
  if WasActive and (Query1.FieldByName('Stock').AsInteger > 0) then
  begin
    TDialogService.ShowMessage('A product with stock cannot be made inactive.');
    Abort;
  end;
  Query1.Edit;
  Query1.FieldByName('UpdatedAt').AsDateTime := Now;
end;

Why it works this way

• The value has not changed yet: Active still holds the old value, and the grid writes the opposite one after the handler.
• The row is the active record: a check box is toggled on the active row, so the dataset’s current record is the row of the event.
• Abort refuses the change: the exception is silent, and the grid does not toggle the value.
• Posting: a toggle posts the row at once when the row was not being edited. Here the handler puts it in edit state first, so the toggle joins that edit and the row is posted with it, when another row becomes active (or when the application posts it). To post at once, handle the field’s OnChange and call Post there instead of editing in this event.

See Also

• OnCheckChange
• Editing
• Examples