Advanced MFC Programming

Chapter 4. Button
can find out whether the current state of the check box is “Checked” or “Unchecked”. Based on this
information, we can decide which bitmap should be used.
Sample 4.2\Btn demonstrates the above method. It is based on sample 4.1\Btn. In the sample, three
new buttons are added: one of them is implemented as a check box; the rest are implemented as radio
buttons. The following describes how the bitmap check box and radio buttons are implemented in the
sample:
1) Add a check box and two radio buttons to the dialog template. Name the IDs of new controls
IDC_CHECK, IDC_RADIO_A and IDC_RADIO_B respectively. In the property sheet that lets us customize
control’s properties, check “Bitmap” check box (Figure 4-4).
Figure 4-4. Set properties for bitmap check box control
2) Add two bitmap resources, one for checked state and one for unchecked state. Their resource IDs are
ID_BITMAP_CHECK and ID_BITMAO_UNCHECK respectively. The bitmaps must have a same size.
3) Declare two CBitmap type variables m_bmpCheck and m_bmpUnCheck in class CBtnDlg, in function
CBtnDlg::OnInitDlg(), call CBitmap::LoadBitmap(…) to load the two bitmap resources. Then call
function CButton::SetBitmap(…) to set bitmap for the check box and radio buttons. In the sample, all
of the new controls are initialized to unchecked state (In order to do this, we need to associate buttons
with m_bmpUnCheck instead of m_bmpCheck). The following code fragment shows the modified class
CBtnDlg and the function CBtnDlg::OnInitDialog(…):
……
……
……
……
……
class CBtnDlg : public CDialog
{
protected:
};
CBitmap m_bmpCheck;
CBitmap m_bmpUnCheck;
BOOL CBtnDlg::OnInitDialog()
{
}
m_bmpCheck.LoadBitmap(IDB_BITMAP_CHECK);
m_bmpUnCheck.LoadBitmap(IDB_BITMAP_UNCHECK);
((CButton *)GetDlgItem(IDC_CHECK))->SetBitmap
(
(HBITMAP)m_bmpUnCheck.GetSafeHandle()
);
((CButton *)GetDlgItem(IDC_RADIO_A))->SetBitmap
(
(HBITMAP)m_bmpUnCheck.GetSafeHandle()
);
((CButton *)GetDlgItem(IDC_RADIO_B))->SetBitmap
(
(HBITMAP)m_bmpUnCheck.GetSafeHandle()
);
4) Declare a new member function CBtnDlg::SetCheckBitmap(…). We will use it to set a button’s bitmap
according to its current state. The function has one parameter nID that identifies the control. Within the
72