截获滚动条消息

截获滚动条消息 　
type
{$IFDEF WIN32}
WParameter = LongInt;
{$ELSE}
WParameter = Word;
{$ENDIF}
LParameter = LongInt;
{Declare a variable to hold the window procedure we are replacing}
var
OldWindowProc : Pointer;
function NewWindowProc(WindowHandle : hWnd;
TheMessage : WParameter;
ParamW : WParameter;
ParamL : LParameter) : LongInt
{$IFDEF WIN32} stdcall; {$ELSE} export; {$ENDIF}
var
TheRangeMin : integer;
TheRangeMax : integer;
TheRange : integer;
begin
if TheMessage = WM_VSCROLL then begin
{Get the min and max range of the horizontal scroll box}
GetScrollRange(WindowHandle,
SB_HORZ,
TheRangeMin,
TheRangeMax);
{Get the vertical scroll box position}
TheRange := GetScrollPos(WindowHandle,
SB_VERT);
{Make sure we wont exceed the range}
if TheRange < TheRangeMin then
TheRange := TheRangeMin else
if TheRange > TheRangeMax then
TheRange := TheRangeMax;
{Set the horizontal scroll bar}
SetScrollPos(WindowHandle,
SB_HORZ,
TheRange,
true);
end;
if TheMessage = WM_HSCROLL then begin
{Get the min and max range of the horizontal scroll box}
GetScrollRange(WindowHandle,
SB_VERT,
TheRangeMin,
TheRangeMax);
{Get the horizontal scroll box position}
TheRange := GetScrollPos(WindowHandle,
SB_HORZ);
{Make sure we wont exceed the range}
if TheRange < TheRangeMin then
TheRange := TheRangeMin else
if TheRange > TheRangeMax then
TheRange := TheRangeMax;
{Set the vertical scroll bar}
SetScrollPos(WindowHandle,
SB_VERT,
TheRange,
true);
end;
{ Call the old Window procedure to }
{ allow processing of the message. }
NewWindowProc := CallWindowProc(OldWindowProc,
WindowHandle,
TheMessage,
ParamW,
ParamL);
end;
　
procedure TForm1.FormCreate(Sender: TObject);
begin
{ Set the new window procedure for the control }
{ and remember the old window procedure. }
OldWindowProc := Pointer(SetWindowLong(ScrollBox1.Handle,
GWL_WNDPROC,
LongInt(@NewWindowProc)));
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
{ Set the window procedure back }
{ to the old window procedure. }
SetWindowLong(ScrollBox1.Handle,
GWL_WNDPROC,
LongInt(OldWindowProc));
end;