How to add mouse wheel support to a component descended from TGraphicControl?

Question

I have created a delphi component which descends from TGraphicControl. Is it possible to add support for mouse wheels?

--- Edit ---

I\'ve exposed the Mou

Answer 1

I'm using the following technique, I subscribe to the form event MouseWheelUp() and inside it, I search for widget with WindowFromPoint() (win32 api function) and Vcl.Controls.FindControl(), then I check if I got the right UI widget, when I don't I check for ActiveControl (widget on the form which currently has focus).

This technique ensures, that the mouse wheel up/down event works when the widget is under the cursor or when it's not under the cursor, but has focus.

The example below reacts to the mouse wheel up event and increments TSpinEdit when TSpinEdit is under the cursor or has a focus.

function TFormOptionsDialog.FindSpinEdit(const AMousePos: TPoint): TSpinEdit;
var
  LWindow: HWND;
  LWinControl: TWinControl;
begin
  Result := nil;

  LWindow := WindowFromPoint(AMousePos);
  if LWindow = 0 then
    Exit;

  LWinControl := FindControl(LWindow);
  if LWinControl = nil then
    Exit;

  if LWinControl is TSpinEdit then
    Exit(LWinControl as TSpinEdit);

  if LWinControl.Parent is TSpinEdit then
    Exit(LWinControl.Parent as TSpinEdit);

  if ActiveControl is TSpinEdit then
    Exit(ActiveControl as TSpinEdit);
end;

procedure TFormOptionsDialog.FormMouseWheelUp(Sender: TObject; Shift: TShiftState; MousePos: TPoint;
  var Handled: Boolean);
var
  LSpinEdit: TSpinEdit;
begin
  LSpinEdit := FindSpinEdit(MousePos);
  if LSpinEdit = nil then
    Exit;

  LSpinEdit.Value := LSpinEdit.Value + LSpinEdit.Increment;
  Handled := True;
end;