Advanced MFC Programming

Chapter 1. Tool Bar and Dialog Bar
Usually we use a Boolean type variable as the flag, which represents “certain situations” in the above
if statement. We can toggle this flag in other functions, this will cause the button state to be changed
automatically. By doing this, the button’s state is synchronized with the variable.
To set check state for a button, all we need to do is calling function CCmdUI::SetCheck(…) instead of
CCmdUI::Enable(…) in the message handler.
Sample
Sample 1.2\Bar demonstrates how to make the four color buttons behave like radio buttons. At any
time, one and only one button will be set to checked state (it will recess and give the user an impression
that it is being held down).
To implement this feature, a member variable m_uCurrentBtn is declared in class CBarDoc. The value
of this variable could be set to any ID of the four buttons in the member functions (other values are not
allowed). In the user-interface update command message handler of each button, we check if the value of
m_nCurrentBtn is the same with the corresponding button’s ID. If so, we need to set check for this button,
otherwise, we remove its check.
The following lists the steps of how to implement these message handlers:
1) Open file “BarDoc.h”, declare a protected member variable m_uCurrentBtn in class CBarDoc:
……
……
class CBarDoc : public CDocument
{
protected:
UINT m_uCurrentBtn;
};
2) Go to file “BarDoc.cpp”, in CBarDoc’s constructor, initialize m_uCurrentBtn red button’s resource ID:
CBarDoc::CBarDoc()
{
m_uCurrentBtn=ID_BUTTON_RED;
}
This step is necessary because we want one of the buttons to be checked at the beginning.
3) Implement UPDATE_COMMAND_UI message mapping for four button IDs. This is almost the same with
adding ON_COMMAND macros, which could be done through using Class Wizard. The only difference
between two implementations is that they select different message types from “Message” window (see
step 5 previous section). Here we should select “UPDATE_COMMAND_UI” instead of
“COMMAND”.
1) Implement the four message handlers as follows:
void CBarDoc::OnUpdateButtonBlue(CCmdUI* pCmdUI)
{
pCmdUI->SetCheck(pCmdUI->m_nID == m_uCurrentBtn);
}
void CBarDoc::OnUpdateButtonGreen(CCmdUI* pCmdUI)
{
pCmdUI->SetRadio(pCmdUI->m_nID == m_uCurrentBtn);
}
void CBarDoc::OnUpdateButtonRed(CCmdUI* pCmdUI)
{
pCmdUI->SetRadio(pCmdUI->m_nID == m_uCurrentBtn);
}
void CBarDoc::OnUpdateButtonYellow(CCmdUI* pCmdUI)
{
pCmdUI->SetRadio(pCmdUI->m_nID == m_uCurrentBtn);
}
10