Delphi event handling, how to create own event

Question

I am new to delphi development. I have to create an event and pass some properties as parameters. Could someone share some demo program that shows how to do this from scratc

Answer 1

You use an event handler to react when something else happens (for example AfterCreation and before closing).

In order to use events for your own class, you need to define the event type. Change the type and number of parameters needed.

type
  TMyProcEvent = procedure(const AIdent: string; const AValue: Integer) of object;
  TMyFuncEvent = function(const ANumber: Integer): Integer of object;

In the class, you can add a DoEvent (rename for the proper event). SO you can call the DoEvent internally. The DoEvent handles the possibility that an event is not assigned.

type
  TMyClass = class
  private
    FMyProcEvent : TMyProcEvent;
    FMyFuncEvent : TMyFuncEvent;
  protected
    procedure DoMyProcEvent(const AIdent: string; const AValue: Integer);
    function DoMyFuncEvent(const ANumber: Integer): Integer;

  public
    property MyProcEvent: TMyProcEvent read FMyProcEvent write FMyProcEvent;
    property MyFuncEvent: TMyFuncEvent read FMyFuncEvent write FMyFuncEvent;
  end;

procedure TMyClass.DoMyProcEvent(const AIdent: string; const AValue: Integer);
begin
  if Assigned(FMyProcEvent) then
    FMyProcEvent(AIdent, AValue);
  // Possibly add more general or default code.
end;


function TMyClass.DoMyFuncEvent(const ANumber: Integer): Integer;
begin
  if Assigned(FMyFuncEvent) then
    Result := FMyFuncEvent(ANumber)
  else
    Result := cNotAssignedValue;
end;