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 MouseWheel events as shown below but they aren't called.

TMyComponent = class(TGraphicControl)
published
  property OnMouseWheel;
  property OnMouseWheelDown;
  property OnMouseWheelUp;
end;

--- Edit ---

As suggested below, I've tried to trap the WM_MOUSEWHEEL and CM_MOUSEWHEEL messages, but it doesn't seem to work. However I've managed to trap the CM_MOUSEENTER message. I don't understand why i can trap one type of message, but not the other.

Answer 1

Trap the WM_MOUSEWHEEL message.

Answer 2

TGraphicControl descends from TControl, which already has mouse-wheel support. See the wm_MouseWheel message, the DoMouseWheel, DoMouseWheelDown, DoMouseWheelUp, and MouseWheelHandler methods, and the WheelAccumulator property.

Answer 3

Only TWinControl descendants can receive mouse wheel messages. TGraphicControl is not a Window based control and therefore can not. It could work if the VCL routes the messages to the TGraphicControl, but apparently does not. You could descend from TCustomControl and then it would work.

Answer 4

I have the same problem. No luck finding solution yet, but maybe this will be helpful:

I suspect the other component is calling the Win API method SetCapture, which according to the API help:

"The SetCapture function sets the mouse capture to the specified window belonging to the current thread. Once a window has captured the mouse, all mouse input is directed to that window, regardless of whether the cursor is within the borders of that window. Only one window at a time can capture the mouse. "

As a new user I can not post a link to the full thread.

EDITED

If you create your component as a descendant from TCustomControl you can solve your problem as described below:

1. Use OnMouseEnter event to detect when mouse enters your component.
2. In OnMouseEnter call SetFocus method to make your component focused. Now your component can receive WM_MOUSEWHEEL message