How can I fix the TScrollBar MouseWheel malfunction?

Question

I have a TScrollBox inside of a TFrame and when I use my mouse's wheel it simply does not goes up nor down the ScrollBox scrolling.

I have tried to use

TScrollBox(Sender).Perform(WM_VSCROLL,1,0); 

on the FrameMouseWheelDown but it does not trigger.

Any Ideas?

Answer 1

My scroll box looks like this:

type
  TMyScrollBox = class(TScrollBox)
  protected
    function DoMouseWheel(Shift: TShiftState; WheelDelta: Integer; MousePos: TPoint): Boolean; override;
    procedure WndProc(var Message: TMessage); override;
  end;

function TMyScrollBox.DoMouseWheel(Shift: TShiftState; WheelDelta: Integer; MousePos: TPoint): Boolean;
begin
  Result := inherited DoMouseWheel(Shift, WheelDelta, MousePos);
  if not Result then begin
    if Shift*[ssShift..ssCtrl]=[] then begin
      VertScrollBar.Position := VertScrollBar.Position - WheelDelta;
      Result := True;
    end;
  end;
end;

procedure TMyScrollBox.WndProc(var Message: TMessage);
begin
  if Message.Msg=WM_MOUSEHWHEEL then begin
    (* For some reason using a message handler for WM_MOUSEHWHEEL doesn't work. The messages
       don't always arrive. It seems to occur when both scroll bars are active. Strangely,
       if we handle the message here, then the messages all get through. Go figure! *)
    if TWMMouseWheel(Message).Keys=0 then begin
      HorzScrollBar.Position := HorzScrollBar.Position + TWMMouseWheel(Message).WheelDelta;
      Message.Result := 0;
    end else begin
      Message.Result := 1;
    end;
  end else begin
    inherited;
  end;
end;

Answer 2

You can use the OnMouseWheel event handler:

ScrollBar1.OnMouseWheel := ScrollBoxMouseWheel;
...
procedure TFrame1.ScrollBoxMouseWheel(Sender: TObject; Shift: TShiftState; WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
begin
  Handled := True;
  if WheelDelta < 0 then
    TScrollBox(Sender).VertScrollBar.Position := TScrollBox(Sender).VertScrollBar.Position + TScrollBox(Sender).VertScrollBar.Increment 
  else
    TScrollBox(Sender).VertScrollBar.Position := TScrollBox(Sender).VertScrollBar.Position - TScrollBox(Sender).VertScrollBar.Increment;
end;