Evenement sur un ScrollBox

Par défaut , il n'en existe pas.
Il cependant possible de les rajouter sur nouveau composant :

voila un exemple pour ajouter 2 evenements :
OnVerticalScrollPosChange
OnHorizontalScrollPosChange

Code du Composant

fichier .h

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//---------------------------------------------------------------------------
 
#ifndef MyScrollBoxH
#define MyScrollBoxH
//---------------------------------------------------------------------------
#include <SysUtils.hpp>
#include <Classes.hpp>
#include <Controls.hpp>
#include <Forms.hpp>
//---------------------------------------------------------------------------
class PACKAGE TMyScrollBox : public TScrollBox
{
private:
 
        TNotifyEvent FOnVerticalScrollPosChange;
        TNotifyEvent FOnHorizontalScrollPosChange;
 
 
protected:
         //evenements
        void __fastcall  VerticalScroll( TWMVScroll &Msg ) ;
        void __fastcall  HorizontalScroll( TWMHScroll &Msg ) ;
public:
        __fastcall TMyScrollBox(TComponent* Owner);
 
         //fonctions pour controler le deplacement du bouton de scroll
        void __fastcall ScrollLineDown();
        void __fastcall ScrollLineUp();
        void __fastcall ScrollPageDown();
        void __fastcall ScrollPageUp();
 
 
        //capture des messages WM_VSCROLL et WM_HSCROLL
        BEGIN_MESSAGE_MAP
            MESSAGE_HANDLER(WM_VSCROLL, TWMVScroll, VerticalScroll)
            MESSAGE_HANDLER(WM_HSCROLL, TWMHScroll, HorizontalScroll)
        END_MESSAGE_MAP(TScrollBox)
 
__published:
 
       __property TNotifyEvent OnHorizontalScrollPosChange={read=FOnHorizontalScrollPosChange,write=FOnHorizontalScrollPosChange};
       __property TNotifyEvent OnVerticalScrollPosChange={read=FOnVerticalScrollPosChange,write=FOnVerticalScrollPosChange};
 
};
//---------------------------------------------------------------------------
#endif

le .cpp

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//---------------------------------------------------------------------------
 
#include <vcl.h>
 
#pragma hdrstop
 
#include "MyScrollBox.h"
#pragma package(smart_init)
 
 
//---------------------------------------------------------------------------
// ValidCtrCheck is used to assure that the components created do not have
// any pure virtual functions.
//
 
static inline void ValidCtrCheck(TMyScrollBox *)
{
        new TMyScrollBox(NULL);
}
//---------------------------------------------------------------------------
__fastcall TMyScrollBox::TMyScrollBox(TComponent* Owner)
        : TScrollBox(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall  TMyScrollBox::VerticalScroll( TWMVScroll &Msg )
{
        if(FOnVerticalScrollPosChange) {
         FOnVerticalScrollPosChange(this);
        }
        TScrollBox::Dispatch(&Msg);
}
//---------------------------------------------------------------------------
void __fastcall  TMyScrollBox::HorizontalScroll( TWMHScroll &Msg )
{
        if(FOnHorizontalScrollPosChange) {
           FOnHorizontalScrollPosChange(this);
        }
        TScrollBox::Dispatch(&Msg);
}
//---------------------------------------------------------------------------
void __fastcall TMyScrollBox::ScrollLineDown()
{
    Perform(WM_VSCROLL,SB_LINEDOWN,NULL);
}
//---------------------------------------------------------------------------
void __fastcall TMyScrollBox::ScrollLineUp()
{
    Perform(WM_VSCROLL,SB_LINEUP,NULL);
}
//---------------------------------------------------------------------------
void __fastcall TMyScrollBox::ScrollPageDown()
{
    Perform(WM_VSCROLL,SB_PAGEDOWN,NULL);
}
//---------------------------------------------------------------------------
void __fastcall TMyScrollBox::ScrollPageUp()
{
    Perform(WM_VSCROLL,SB_PAGEUP,NULL);
}
 
//---------------------------------------------------------------------------
namespace Myscrollbox
{
        void __fastcall PACKAGE Register()
        {
                 TComponentClass classes[1] = {__classid(TMyScrollBox)};
                 RegisterComponents("Developpez.com", classes, 0);
        }
}
//---------------------------------------------------------------------------

voici un exmple d'utilisation après installation:

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// nouvel evenement 
void __fastcall TForm1::MyScrollBox1VerticalScrollPosChange(
      TObject *Sender)
{
 
        ProgressBar1->Position = MyScrollBox1->VertScrollBar->Position;
 
}