Advanced MFC Programming

Chapter 2. Menu
with adding other types of resources: we can execute Insert | Resource… command, then select Bitmap
from the popped up dialog box. The newly added resource will be assigned a default ID, it could also be
changed by the programmer.
To load a bitmap resource into the memory, we need to use class CBitmap. This procedure is similar to
loading a menu resource: first we need to use CBitmap to declare a variable, then call function
CBitmap::LoadBitmap(…) to load the resource. For example, if we have a CBitmap type variable bmp, and
our bitmap resource’s ID is IDB_BITMAP, we can load the bitmap as follows:
bmp.LoadBitmap(IDB_BITMAP);
When calling function CMenu::SetMenuItemBitmaps(…), we can pass the pointers of CBitmap type
variables to its parameters.
Sample 2.4\Menu demonstrates bitmap check implementation. It is based on sample 2.3\Menu, which
adds check bitmaps to menu item ID__POPUPITEM1 and ID__POPUPITEM2. Two bitmap resources
IDB_BITMAP_CHECK and IDB_BITMAP_UNCHECK are used to indicate menu item’s checked and unchecked
states respectively. Both bitmaps have a size of 15×15, which is a suitable size for normal menu items. If
we use bigger bitmaps, they might be chopped to fit into the area of menu item.
In the sample, two new CBitmap type variables m_bmpCheck and m_bmpUnCheck are declared in class
CMenuDoc, which are used to load the bitmap resources:
……
class CMenuDoc : public CDocument
{
protected:
CMenu m_menuSub;
CBitmap m_bmpCheck;
CBitmap m_bmpUnCheck;
BOOL m_bSubMenuOn;
}
In the constructor of CMenuDoc, bitmap resources IDB_BITMAP_CHECK and IDB_BITMAP_UNCHECK are
loaded using two variables. Also, after we load the pop up menu resource, function CMenu::
SetMenuItemBitmap(…) is called for both ID__POPUPITEM1 and ID__POPITEM2. We use bitmaps to indicate
both checked and unchecked states. The following code fragment shows how it is implemented:
CMenuDoc::CMenuDoc()
{
CMenu *ptrMenu;
}
m_menuSub.LoadMenu(IDR_MENU_POPUP);
m_bmpCheck.LoadBitmap(IDB_BITMAP_CHECK);
m_bmpUnCheck.LoadBitmap(IDB_BITMAP_UNCHECK);
ptrMenu=m_menuSub.GetSubMenu(0);
ptrMenu->SetMenuItemBitmaps(0, MF_BYPOSITION, &m_bmpUnCheck, &m_bmpCheck);
ptrMenu->SetMenuItemBitmaps(1, MF_BYPOSITION, &m_bmpUnCheck, &m_bmpCheck);
m_bSubMenuOn=FALSE;
When calling function CMenu::SetMenuItemBitmap(…), we use absolute position instead of command
ID to identify a menu item. So the second parameter passed to the function is MF_BYPOSITION.
Besides these, two UPDATE_COMMAND_UI message handlers are also added to CMenuDoc to set item
ID__POPUPITEM1 to checked state and set ID_POPUPITEM2 to unchecked state permenently. The following
two functions show the implementation of the messages handlers:
void CMenuDoc::OnUpdatePopUpItem1(CCmdUI *pCmdUI)
{
if(m_bSubMenuOn)pCmdUI->SetCheck(TRUE);
}
void CMenuDoc::OnUpdatePopUpItem2(CCmdUI *pCmdUI)
{
if(m_bSubMenuOn)pCmdUI->SetCheck(FALSE);
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