How to set a value of another Grid column during editing of a cell

Description:
Assume a situation where a value of one of two adjacent grid columns depends on another column's value. The first column's value must be changed when a user has edited a value of the second column. How to accomplish this with the ExpressQuantumGrid?

Answer:
Basically, we recommend that you implement such tasks at the dataset level. For example, when a particular field is updated, you may change the other field's value within the field's OnChange event handler or within the dataset's BeforePost event handler.
This, however, applies only to data-aware Views. When working with an unbound View, please use the Data Controller's OnRecordChanged event (it is fired when record data is changed).
You may also try the following approach which can be used for all types of View:
During editing the Data Controller caches edited values and save them to the Values list only after posting. The Data Controller provides two methods to work with edited values: GetEditValue and SetEditValue. You need to use just these methods to work with editing data; the GetValue and SetValue methods are not appropriate for this task.
The Grid's in-place editor provides a number of events, which you can use to handle value changes in the editor. They are OnChange, OnEditValueChanged and OnValidate. We used the OnEditValueChanged event in our sample project and obtained the current edit value via the editor's EditValue property (see the "How to get a new value within the OnEditValueChanged or OnChange event handlers" article).

Delphi
// Delphi code  
uses
  cxVariants, cxDataUtils;

procedure TfrmMain.viewOrdersAmountPaidPropertiesEditValueChanged(
  Sender: TObject);
var
  Edit: TcxCustomEdit;
  Value: Double;
  View: TcxGridDBTableView;
  FreightColumn: TcxGridColumn;
begin
  Edit := Sender as TcxCustomEdit;
  if VarIsNumericEx(Edit.EditValue) then
  begin
    Value := Edit.EditValue;

    Edit.PostEditValue;  // To 'stick' the new value in the active cell

    View := cxGrid.FocusedView as TcxGridDBTableView;
    FreightColumn := View.GetColumnByFieldName('Freight');
    View.DataController.SetEditValue(FreightColumn.Index, Value/5, evsValue);
  end;
end;

NOTE: The SetEditValue method has the benefit that the Grid automatically restores a previous value, if a user has decided to abandon changes and pressed Esc.
See Also:
How to add or delete records in Smart Refresh mode
How to get a new value within the OnEditValueChanged or OnChange event handlers