Make a new DBLookupComboBox-Component with OnChange-Event

Problem/Question/Abstract:

DB-Aware Components like TDBEdit have an Event "OnChange". This Event is established in TCustomEdit.
Unfortunately in TDBLookupComboBox there is no OnChange-Event, because this component is not based on TCustomEdit but on TWinControl.
What to do if you want to have an OnChange event in a DBLookupComboBox?

Answer:

DB-Aware Components like TDBEdit have an Event "OnChange". This Event is established in TCustomEdit.

Unfortunately in TDBLookupComboBox there is no OnChange-Event, because this component is not based on TCustomEdit but on TWinControl.

What to do if you want to have an OnChange event in a DBLookupComboBox?

Well, let's build our own component with this event! It's easy  because TDBLookupControl established an protected Procedure "KeyValueChanged". It will fired when the property "KeyValue" ist changed.

So we can overwrite this Event in our own Componentent and call a new Event "OnChang".
That's all :-)

type

  TMyDBLookupComboBox = class(TDBLookupComboBox)
  private
    FOnChange: TNotifyEvent;
  protected
    procedure KeyValueChanged; override;
  published
    property OnChange: TNotifyEvent read FOnChange write FOnChange;
  end;

implementation

procedure TMyDBLookupComboBox.KeyValueChanged;
begin
  inherited;
  if Assigned(FOnChange) then
    FOnChange(Self);
end;