Separate module for closing TPageControl tabs

[BIT]

Hello, can this code be saved in separate modules and used in the main form for the TPageControl component
close tab icon.
I do not know how to work with classes))

Code: Pascal  [Select][+][-]

1. unit PageControlButtonClose;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, ComCtrls, LCLType, Controls, types, Graphics, LCLIntf;
9.  
10. type
11.  
12.   { TPageControl }
13.   TPageControl = class(ComCtrls.TPageControl)
14.   private
15.   const
16.     btnSize = 14;
17.  
18.   protected
19.     procedure MouseDown(Button: TMouseButton; Shift: TShiftState;
20.       X, Y: integer); override;
21.     procedure PaintWindow(DC: HDC); override;
22.   end;
23.  
24. implementation
25.  
26. { TPageControl }
27.  
28. procedure TPageControl.MouseDown(Button: TMouseButton; Shift: TShiftState;
29.   X, Y: integer);
30.  
31. var
32.   R: TRect;
33. begin
34.   inherited MouseDown(Button, Shift, X, Y);
35.   if Button = mbLeft then
36.   begin
37.     R := TabRect(ActivePageIndex);
38.     if PtInRect(Classes.Rect(R.Right - btnSize - 5, R.Top + 4,
39.       R.Right - 5, R.Top + btnSize + 4), Classes.Point(X, Y)) then
40.     begin
41.  
42.       ActivePage.Free;
43.     end;
44.  
45.   end;
46. end;
47.  
48. procedure TPageControl.PaintWindow(DC: HDC);
49. var
50.   i: integer;
51.   R: TRect;
52.   bm: TBitmap;
53. begin
54.   inherited PaintWindow(DC);
55.  
56.   bm := TBitmap.Create;
57.   try
58.     bm.SetSize(16, 16);
59.    Images.GetBitmap(0, bm);
60.  
61.     for i := 0 to Pred(PageCount) do
62.     begin
63.       R := TabRect(i);
64.    
65.       StretchBlt(DC, R.Right - btnSize - 4, R.Top + 2,
66.         btnSize, btnSize, bm.Canvas.Handle, 0, 0, 16, 16, cmSrcCopy);
67.     end;
68.   finally
69.     bm.Free;
70.   end;
71. end;
72.  
73. end.

[BIT]

This code does not work when connected to the main form from a separate module. If this code is inserted into the main form it works fine. The question is how to use this code from the plug-in in the main one?

[Awkward]

Easy to use... LCL must be patched ^_^

[zamtmn]

This is a hack based on class substitution, it will not work in a separate module

[Zvoni]

Why not write as a class helper? (instead of inheritance)

[korba812]

Why not write as a class helper? (instead of inheritance)

Because you can't override virtual methods this way.

[Zvoni]

Why not write as a class helper? (instead of inheritance)

Because you can't override virtual methods this way.

https://wiki.freepascal.org/Helper_types#Method_hiding

Restrictions

A helper type may not

    contain (class) destructors (except in trunk FPC 3.3.1)
    contain class constructors (except in trunk FPC 3.3.1)
    contain fields
    contain abstract methods
    "override" virtual methods of the extended class (they can be hidden by the helper though)

Methods of the extended type can be overloaded (thus they are not hidden by the helper) by using the overload keyword.

A call to Inherited MethodName should still work, or not?
No, it doesn't, but the question remains: Does he even need to call the "Ancestor"-Method?

[BIT]

This is a hack based on class substitution, it will not work in a separate module

If you place the unit at the end or after the unit that houses the original class the compiler should see that one first in the local uses list.

Thank you earned!