Usually, pop-up menus are “attached” to another menu; they appear when the user selects a command on that menu. However, Windows also lets you provide “floating” pop-up menus, which appear at the current cursor position when the user presses a certain key or clicks a mouse button.
To provide a floating pop-up menu, you use the CreatePopupMenu and TrackPopupMenu functions. If you want the floating pop-up menu to appear when the user presses a certain key or mouse button, create the floating pop-up menu within the case statement that handles the input message from that key or button.
The following example displays a floating pop-up menu when the user depresses the right mouse button:
POINT currentpoint;
.
.
.
case WM_RBUTTONDOWN:
{
HWND hWnd; /* handle to current window */
HMENU hFloatingPopup; /* handle for floating pop-up */
1 currentpoint = MAKEPOINT (lParam);
/* point at which the user
pressed the button */
.
.
.
2 hFloatingPopup = CreatePopupMenu();
3 AppendMenu (hFloatingPopup,
MF_ENABLED,
IDM_CALC,
“Calculator”);
AppendMenu (hFloatingPopup,
MF_ENABLED,
IDM_CARDFILE,
“Cardfile”);
AppendMenu (hFloatingPopup,
MF_ENABLED,
IDM_NOTEPAD,
“Notepad”);
4 ClientToScreen (hWnd, (LPPOINT)¤tpoint);
5 TrackPopupMenu (hFloatingPopup,
NULL,
6 currentpoint.x,
currentpoint.y,
NULL,
hWnd,
NULL);
7 DestroyMenu (hFloatingPopup);
break;
}
In this example:
| 1 | The lParam parameter of the WM_RBUTTONDOWN message contains the current position of the mouse. The MAKEPOINT function converts this long value to a point, which is then stored in the currentpoint data structure. |
| 2 | The CreatePopupMenu function creates an empty pop-up menu, and returns a handle to that menu. The new menu's handle is placed in the variable hFloatingPopup. |
| 3 | After creating the empty pop-up menu, the application appends three items to it: Calculator, Cardfile, and Notepad. |
| 4 | The ClientToScreen function converts the coordinates of the current cursor position so that they describe the position relative to the entire screen's upper-left corner. (Initially, the coordinates describe the cursor position relative to the client window instead). |
| 5 | Once the menu is complete, the application displays it at the current cursor position by calling TrackPopupMenu. |
| 6 | The x and y fields of the currentpoint data structure contain the current screen coordinates of the cursor. |
| 7 | After the user has made a selection from the menu, the application destroys the menu, thereby freeing up the memory the menu used. The application re-creates the menu each time the user depresses the right mouse button. |