Delphi / TFormAsInterface

Test003.dpr

program Test003;

uses
  FastMM4 in '..\..\..\VCL\FastMM4\FastMM4.pas',
  FastMM4Messages in '..\..\..\VCL\FastMM4\FastMM4Messages.pas',
  Vcl.Forms,
  Unit1 in 'Unit1.pas' {Form1},
  Unit2 in 'Unit2.pas' {Form2},
  Unit3 in 'Unit3.pas';

{$R *.res}

begin
  Application.Initialize;
  Application.MainFormOnTaskbar := True;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.

Unit1.dfm

object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 290
  ClientWidth = 554
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  PixelsPerInch = 96
  TextHeight = 13
  object Button1: TButton
    Left = 124
    Top = 64
    Width = 75
    Height = 25
    Caption = 'Button1'
    TabOrder = 0
    OnClick = Button1Click
  end
end

Unit1.pas

unit Unit1;

interface

uses
  Unit3,
  //
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
  public
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

uses
  Unit2;

procedure TForm1.Button1Click(Sender: TObject);
var
  LForm2: IForm2;
begin
  LForm2 := CreateForm2(Self);
  try
    LForm2.CallbackProc;
  finally
    LForm2 := nil;
  end;
end;

end.

Unit2.dfm

object Form2: TForm2
  Left = 0
  Top = 0
  Caption = 'Form2'
  ClientHeight = 290
  ClientWidth = 554
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  PixelsPerInch = 96
  TextHeight = 13
end

Unit2.pas

unit Unit2;

interface

uses
  Unit3,
  //
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs;

type
  IForm2 = interface(ICallbackForm)
    ['{D0204F6D-3F49-4B48-9105-0FB291CD72B3}']
  end;

  TForm2 = class(TForm, IInterface, IForm2)
  strict private
    FOwnerIsComponent: Boolean;
    FRefCount: Integer;
  protected
    function _AddRef: Integer; stdcall;
    function _Release: Integer; stdcall;
  public
    class function NewInstance: TObject; override;
    destructor Destroy; override;
  public
    procedure AfterConstruction; override;
    procedure BeforeDestruction; override;
  public
    procedure CallbackProc;
  end;

function CreateForm2(AOwner: TComponent): IForm2;

implementation

{$R *.dfm}

function CreateForm2(AOwner: TComponent): IForm2;
begin
  Result := TForm2.Create(AOwner);
end;

{ TForm2 }

destructor TForm2.Destroy;
begin
  ShowMessage('TForm2.Destroy');

  Destroying;
  if FOwnerIsComponent and (FRefCount > 1) then
  begin
    //
  end;

  inherited;
end;

function TForm2._AddRef: Integer;
begin
  Result := InterlockedIncrement(FRefCount)
end;

function TForm2._Release: Integer;
begin
  Result := InterlockedDecrement(FRefCount);
  if (Result = 0) then
  begin
    if FOwnerIsComponent then
      Owner.RemoveComponent(Self);
    Destroy;
  end;
end;

class function TForm2.NewInstance: TObject;
begin
  Result := inherited NewInstance;
  TForm2(Result).FRefCount := 1;
end;

procedure TForm2.AfterConstruction;
begin
  FOwnerIsComponent := Assigned(Owner) and (Owner is TComponent);
  InterlockedDecrement(FRefCount);

  inherited;
end;

procedure TForm2.BeforeDestruction;
{$ifdef DEBUG}
var
  WarningMessage: string;
{$endif DEBUG}
begin
  if (FRefCount <> 0) then
  begin
    if not FOwnerIsComponent then
      System.Error(reInvalidPtr)
{$ifdef DEBUG}
    else
    begin
      WarningMessage := Format(
        'Trying to destroy an Owned TForm2 of class %s named %s that still has %d interface references left',
        [ClassName, Name, FRefCount]);
      OutputDebugString(PChar(WarningMessage));
    end;
{$endif DEBUG}
  end;

  inherited;
end;

procedure TForm2.CallbackProc;
begin
  ShowMessage('CallbackProc');
end;

end.

Unit3.pas

unit Unit3;

interface

uses
  System.Classes,
  Vcl.Forms;

type
  ICallbackForm = interface(IInterfaceComponentReference)
    ['{59080B84-94C6-4572-9120-6722FC78758A}']

    procedure CallbackProc;
  end;

implementation

end.