How do I scroll a TScrollbar using the mouse wheel? - delphi

Question

I have a TScrollBar having a code in the OnScroll event.
I want to scroll it using the mouse wheel, but turning the mouse wheel does not scroll the scroll bar and does not trigger the OnScroll event.
Any idea?

Answer 1

procedure TForm1.FormMouseWheel(Sender: TObject; Shift: TShiftState;
WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
var
I: Integer;
begin
Handled := PtInRect(ScrollBox1.ClientRect, ScrollBox1.ScreenToClient(MousePos));
if Handled then
for I := 1 to Mouse.WheelScrollLines do
try
if WheelDelta > 0 then
ScrollBox1.Perform(WM_VSCROLL, SB_LINEUP, 0)
else
ScrollBox1.Perform(WM_VSCROLL, SB_LINEDOWN, 0);
finally
ScrollBox1.Perform(WM_VSCROLL, SB_ENDSCROLL, 0);
end;
end;

Answer 2

The default TScrollBar component indeed seems not to have the OnMouseWheel* events present. But you can simply assign them, as follows:
type
TForm1 = class(TForm)
ScrollBar1: TScrollBar;
procedure FormCreate(Sender: TObject);
procedure ScrollBar1Scroll(Sender: TObject; ScrollCode: TScrollCode;
var ScrollPos: Integer);
private
procedure ScrollBarMouseWheel(Sender: TObject; Shift: TShiftState;
WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
end;
...
procedure TForm1.FormCreate(Sender: TObject);
begin
ScrollBar1.OnMouseWheel := ScrollBarMouseWheel;
end;
procedure TForm1.ScrollBarMouseWheel(Sender: TObject; Shift: TShiftState;
WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
var
NewScrollPos: Integer;
begin
NewScrollPos := ScrollBar1.Position - WheelDelta;
//Trigger the OnScroll event:
ScrollBar1.Scroll(scPosition, NewScrollPos);
//Scroll the bar into the new position:
ScrollBar1.Position := NewScrollPos;
Handled := True;
end;
You are free to implement this some more creative:
if WheelDelta > 0 then
NewScrollPos := ScrollBar1.Position - ScrollBar1.PageSize
else
NewScrollPos := ScrollBar1.Position + ScrollBar1.PageSize;
And you could interpose the TScrollBar class to prevent to assign the event at runtime:
type
TScrollBar = class(StdCtrls.TScrollBar)
protected
function DoMouseWheel(Shift: TShiftState; WheelDelta: Integer;
MousePos: TPoint): Boolean; override;
end;
function TScrollBar.DoMouseWheel(Shift: TShiftState; WheelDelta: Integer;
MousePos: TPoint): Boolean;
var
NewScrollPos: Integer;
begin
NewScrollPos := Position - WheelDelta;
Scroll(scPosition, NewScrollPos);
Position := NewScrollPos;
Result := True;
end;

Answer 3

it's too easy just increase the position Value .
procedure TForm1.FormMouseWheel(Sender: TObject; Shift: TShiftState;
WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
begin
self.VertScrollBar.Position := self.VertScrollBar.Position + WheelDelta;
end;

Answer 4

I don't know if this will help much, but here's how to do it with a TMemo. The scrollbar would have to be a similar process, unless there is some other better way that Delphi versions later than mine use.
procedure TForm1.Memo1WindowProc(var msg: TMessage);
var
ticks: ShortInt;
ScrollMsg: TWMVScroll;
begin
if msg.Msg = WM_MOUSEWHEEL then
begin
ScrollMsg.Msg := WM_VSCROLL;
ticks := HiWord(msg.wparam);
if ticks > 0 then
ScrollMsg.ScrollCode := sb_LineUp
else
ScrollMsg.ScrollCode := sb_LineDown;
ScrollMsg.Pos:=0;
Memo1.Dispatch(ScrollMsg) ;
end
else
OldMemo1(msg);
end;
procedure TForm1.FormCreate(Sender: TObject);
// save old window proc, assign mine.
begin
OldMemo1 := Memo1.WindowProc;
Memo1.WindowProc := Memo1WindowProc;
end;
HTH some.

Answer 5

procedure TForm1.FormMouseWheelDown(Sender: TObject; Shift: TShiftState;
MousePos: TPoint; var Handled: Boolean);
begin
ScrollBox1.VertScrollBar.Position := ScrollBox1.VertScrollBar.Position + 20;
end;
procedure TForm1.FormMouseWheelUp(Sender: TObject; Shift: TShiftState;
MousePos: TPoint; var Handled: Boolean);
begin
ScrollBox1.VertScrollBar.Position := ScrollBox1.VertScrollBar.Position - 20;
end;

Answer 6

Old post, but I found solution. Simply do
procedure TForm1.FormMouseWheel(Sender: TObject; Shift: TShiftState;
WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
begin
inherited;
ScrollBox1.ScrollBy(WheelDelta, 0);
end;
Works for me.

Answer 7

Again this is an old post, and it got me most of the way to what i wanted but a little further tweak to the answer by Stefan, restricting scrolling to when the mouse is over the scrollbar. This detects that the mouse is over the scrollbar (non-client area) of the scroll box before accepting the mousewheel input./ I need this because my scollbox contained comboboxes which users wanted to be able to scrool with the wheel, as well as scrolling the scrollbox (or whatever control is using a scrollbar):
Handled := PtInRect(scrollbox.BoundsRect, scrollbox.ScreenToClient(MousePos))
and not PtInRect(scrollbox.ClientRect, scrollbox.ScreenToClient(MousePos));
if Handled then
for I := 1 to Mouse.WheelScrollLines do
try
if WheelDelta > 0 then
scrollbox.Perform(WM_VSCROLL, SB_LINEUP, 0)
else
scrollbox.Perform(WM_VSCROLL, SB_LINEDOWN, 0);
finally
scrollbox.Perform(WM_VSCROLL, SB_ENDSCROLL, 0);
end;