How to host an IContextMenu, part 2 - Displaying the context menu
Instead of
invoking a fixed verb,
we'll ask the user to choose
from the context menu and invoke the result.
Make these changes to the OnContextMenu function:
#define SCRATCH_QCM_FIRST 1
#define SCRATCH_QCM_LAST 0x7FFF
#undef HANDLE_WM_CONTEXTMENU
#define HANDLE_WM_CONTEXTMENU(hwnd, wParam, lParam, fn) \
((fn)((hwnd), (HWND)(wParam), GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam)), 0L)
// WARNING! Incomplete and buggy! See discussion
void OnContextMenu(HWND hwnd, HWND hwndContext, int xPos, int yPos)
{
POINT pt = { xPos, yPos };
if (pt.x == -1 && pt.y == -1) {
pt.x = pt.y = 0;
ClientToScreen(hwnd, &pt);
}
IContextMenu *pcm;
if (SUCCEEDED(GetUIObjectOfFile(hwnd, L"C:\\Windows\\clock.avi",
IID_IContextMenu, (void**)&pcm))) {
HMENU hmenu = CreatePopupMenu();
if (hmenu) {
if (SUCCEEDED(pcm->QueryContextMenu(hmenu, 0,
SCRATCH_QCM_FIRST, SCRATCH_QCM_LAST,
CMF_NORMAL))) {
int iCmd = TrackPopupMenuEx(hmenu, TPM_RETURNCMD,
pt.x, pt.y, hwnd, NULL);
if (iCmd > 0) {
CMINVOKECOMMANDINFOEX info = { 0 };
info.cbSize = sizeof(info);
info.fMask = CMIC_MASK_UNICODE;
info.hwnd = hwnd;
info.lpVerb = MAKEINTRESOURCEA(iCmd - SCRATCH_QCM_FIRST);
info.lpVerbW = MAKEINTRESOURCEW(iCmd - SCRATCH_QCM_FIRST);
info.nShow = SW_SHOWNORMAL;
pcm->InvokeCommand((LPCMINVOKECOMMANDINFO)&info);
}
}
DestroyMenu(hmenu);
}
pcm->Release();
}
}
The first change addresses the first issue brought up in the
discussion of the WM_CONTEXTMENU message
and fixes the HANDLE_WM_CONTEXTMENU message.
The second change addresses the second issue, and that's the
special handling of keyboard-invoked context menus.
When we receive a keyboard-invoked context menu, we move it to
the (0, 0) position of our client area. This keeps the context
menu displayed in a vaguely sane position.
(If we were a container with objects, it would have been better
to display the context menu over the selected sub-object.)
The third change actually does what we're talking about:
Displaying the context menu to the user, collecting the result,
and acting on it.
You are certainly familiar with
the TrackPopupMenuEx function.
Here we use the TPS_RETURNCMD flag to indicate that the item the
user selected should be returned by the function instead of being
posted as a WM_COMMAND to our window.
This highlights the importance of the fact that
SCRATCH_QCM_FIRST is 1 and not zero.
If it were zero, then we wouldn't be able to distinguish
between the user selecting item zero and the user cancelling the menu.
Once we are confident that the user has selected an item
from the menu, we fill out a
CMINVOKECOMMANDEX structure,
specifying the user's selection in the two verb fields and
indicating the invocation point via the ptInvoke member.
Note that when you invoke a command by menu ID, you must
specify the offset of the menu item
relative to the starting point passed to
IContextMenu::QueryContextMenu.
That's why we subtracted SCRATCH_QCM_FIRST.
When you run this program, you may notice that some things
don't quite work. Most obviously, the Open With and Send To submenus
don't work, but there are more subtle bugs too.
We'll address them over the next few days.
