unit testLabel2;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  StdCtrls;

type
  TtestLabel = class(TLabel)
   public 
    FoldWndProc:TWndMethod;
    constructor Create(AOwner: TComponent);override; 
    destructor  Destroy;override; 
    procedure   MyWndProc(var Message: TMessage);
  end; 

procedure Register;

implementation

procedure Register;
begin  RegisterComponents('Samples', [TtestLabel]);
end;

constructor TtestLabel.Create(AOwner: TComponent); 
begin inherited; 
  if (AOwner is TCustomForm) then
  begin
   FOldWndProc := TCustomForm(AOwner).WindowProc;
   TCustomForm(AOwner).WindowProc := MyWndProc;
  end else begin
   FOldWndProc := nil;
  end;
end;

    //-------------------------------
    //メソッドが一致するかどうか調べる関数
    function SameMethod(const A, B: TWndMethod): Boolean;
    begin
      if (TMethod(A).Code = TMethod(B).Code) and (TMethod(A).Data = TMethod(B).Data) then
        Result := True
      else
        Result := False;
    end;

destructor TtestLabel.Destroy;
begin
  if SameMethod(
    Self.MyWndProc,
    TCustomForm(Owner).WindowProc ) then
  begin
    TCustomForm(Owner).WindowProc := FoldWndProc
  end else
  begin
    raise EComponentError.Create('サブクラス化解除失敗');
  end;

  inherited;
end;

procedure TtestLabel.MyWndProc(var Message: TMessage); 
begin
  case Message.Msg of 

  WM_CHAR: begin  //コンポーネントの動作チェック用
     text:=Char(Message.WPARAM);
   if assigned(FoldWndProc) then FoldWndProc(Message);
   end;

  else if assigned(FoldWndProc) then FoldWndProc(Message);
  end; 
end; 


end.