Блокирование закладок TPageControl

unit GSPageControl;


interface

uses
  Windows, Messages, Types, SysUtils, Classes, Controls, ComCtrls, CommCtrl;

type
  TGSPageControl = class(TPageControl)
  private
    FNewPageIndex, FNotifyIndex: Integer;
    FTab:boolean;
  protected
    function GetTabFromCursor: Integer;
    function CanChange: Boolean; override;
    procedure WMKeyDown(var Message: TWMKey); message WM_KEYDOWN;
    procedure CMDialogKey(var Message: TCMDialogKey); message CM_DIALOGKEY;
  public
    property NewPageIndex: Integer read FNewPageIndex;
    constructor Create(AOwner: TComponent); override;
  end;

procedure Register;

implementation

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

{ TGSPageControl }

function TGSPageControl.CanChange: Boolean;
begin
  if fTab then FNewPageIndex:=FNotifyIndex else
  FNewPageIndex := GetTabFromCursor;
  if FNewPageIndex = -1 then
    FNewPageIndex := FNotifyIndex;
  Result := inherited CanChange;
  FNewPageIndex := -1;
  fTab:=false;
end;

procedure TGSPageControl.CMDialogKey(var Message: TCMDialogKey);
begin
  fTab:=true;
  if (Focused or Windows.IsChild(Handle, Windows.GetFocus)) and
    (Message.CharCode = VK_TAB) and (GetKeyState(VK_CONTROL) < 0) then
    FNotifyIndex := FindNextPage(ActivePage, True, False).TabIndex;
  inherited;
end;

constructor TGSPageControl.Create(AOwner: TComponent);
begin
  inherited;
  FNotifyIndex := 0;
  FNewPageIndex := 0;
  FTab:=false;
end;

function TGSPageControl.GetTabFromCursor: Integer;
var
  HitTestInfo: TTCHitTestInfo;
  P: TPoint;
begin
  GetCursorPos(P);
  HitTestInfo.pt := Self.ScreenToClient(P);
  HitTestInfo.flags := TCHT_ONITEM;
  Result := SendMessage(Self.Handle, TCM_HITTEST, 0, Integer(@HitTestInfo));
end;

procedure TGSPageControl.WMKeyDown(var Message: TWMKey);
begin
  with Message do
    case Message.CharCode of
      37: FNotifyIndex := FindNextPage(ActivePage, False, False).TabIndex;
      39: FNotifyIndex := FindNextPage(ActivePage, True, False).TabIndex;
    end;
  inherited;
end;

end.

Использование:

procedure TForm1.GSPageControl1Changing(Sender: TObject;
  var AllowChange: Boolean);
begin
 AllowChange:=GSPageControl1.Pages[GSPageControl1.NewPageIndex].Enabled
end;