Form Inheritance created in Runtime

Question

Follow the code below:

type
  TfObject = class(TForm)
  private
    procedure FormShow(Sender : TObject);
    procedure FormKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
  public
    constructor Create(AOwner : TComponent); override;
    { Public declarations }
  end;

Create code:

constructor TfObject.Create(AOwner : TComponent);
begin
  inherited Create(AOwner);

  Position := TPosition.poScreenCenter;
  WindowState := wsNormal;
  KeyPreview := true;
  AlphaBlend := true;
  AlphaBlendValue := 0;
  BorderStyle := bsSizeable;

  OnShow := FormShow;
  OnKeyDown := FormKeyDown;
  OnClose := FormClose;
end;

The problem is this, according to what I know related to Delphi with O.O.O., I could use this way to inherit the methods contained in the Father class, but when I do so, I cannot use the inherited in the daughter class, which is in this case the form that is inheriting from TfObject.

I found that by doing the class this way, I can normally use the form methods, but when I put to the form methods (OnShow, OnClose, OnKeyDown) to receive his proper methods, he behaves as if the daughter class were doing this.

Now my question...

How I do for my class TForm assign your form methods and I just inherit them when I implement a method (OnShow, OnClose, OnKeyDown)?

Example:

procedure TForm1.FormShow(sender : TObject);
begin
  //faz algo
  inherited;
  //faz algo
end;

Answer 1

You are assigning an event and not method directly. I suggest looking at the Tcustomform class that is the parent class of Tform, there are methods that can be overridden. So, use Doshow, Doclose, etc. These call events, but can be replaced. See the example:

type
  TForm7 = class(TForm)
  protected
    procedure MetodoSubstituivel; virtual;
    procedure DoShow; override;
  public

  end;

implementation

procedure TForm7.DoShow;
begin
  showmessage('antes');
  inherited;
  showmessage('depois');
end;

procedure TForm7.MetodoSubstituivel;
begin
  //algo aqui
end;

Answer 2

Ramon, I confess I don’t quite understand your need. You want the event of the daughter class not to happen unless called explicitly?

Answer 3

To use inherited in a daughter class method, calling the parent class method, it must be declared as the virtual directive in the parent class and override in the daughter class.