Advanced MFC Programming

Chapter 4. Button
Now we can remove or modify bitmap button IDC_PLAY’s caption text “Play. Actually, it doesn’t
matter if the button has caption text or not. By compiling the application and executing it at this point, we
will see that the bitmap button implemented here is exactly the same as the one implemented in the
previous sample.
4.4 Bitmap Check Box and Radio Button: Method 2
In sample 4.2\Btn, although we can represent the checked and unchecked states of a check box or a
radio button using different bitmaps, we could not customize their “focused” state. When a button has the
current focus, a rectangle with dashed border will always be put over button’s face (Figure 4-5). This is
because we use CButton instead of CBitmapButton to implement buttons, this allows only one bitmap to be
associated with a button.
A rectangle with
dashed border will
appear whenever the
control has current
focus
Figure 4-5. Bitmap check box and radio buttons implemented using class CButton
To improve this, we can use class CBitmapButton to create both check box and radio button. By doing
this, the button’s focused state will be implemented using the bitmap image provided by the programmer
instead of drawing a rectangle with dashed border over button’s face. Since class CBitmapButton supports
only push button implementation, we need to change the bitmap by ourselves to imitate check box and
radio button.
Sample 4.4\Btn is based on sample 4.3\Btn. In this sample, three new buttons are added to the dialog
template: one will be implemented as a check box; the other two will be implemented as radio buttons. All
of them will be based on class CBitmapButton.
First, we need a Boolean type variable for each check box and radio button to represent its current
state. This variable toggles between TRUE and FALSE, indicating if the button is currently checked or
unchecked. When the state of a button changes, we re-associate the button with an alternate bitmap and
paint the bitmap button again.
Since we use push button to implement check box and radio button, we can not call function
CButton::GetCheck(…) to examine if the button is currently checked or not. This is because a push button
will automatically resume to the “up” state after the mouse is released.
In the sample application, three new buttons are added to the dialog template IDD_BTN_DIALOG, and
their corresponding IDs are IDC_BMP_CHECK, IDC_BMP_RADIO_A, IDC_BMP_RADIO_B respectively. Also, they
all have a “Owner draw” style. Besides the new controls, two new bitmap resources are also added to the
application, which will be used to implement button’s “Checked” and “Unchecked” states. The IDs of the
new bitmap resources are IDB_BITMAP_BTNCHECK and IDB_BITMAP_BTNUNCHECK. The difference between the
new bitmaps and two old ones (whose IDs are IDB_BITMAP_CHECK and IDB_BITMAP_UNCHECK) is that the
new bitmaps have a 3-D effect. In sample 4.2\Btn, the check box and radio buttons are implemented using
class CButton, which automatically adds 3-D effect to the controls. Since we want the controls to be
implemented solely by programmer-provided bitmaps, we need to add 3-D effect by ourselves.
In the sample application, three new CBitmapButton type variables are declared in class CBtnDlg. Also,
a new member function SetRadioBitmap() is added to associate bitmaps with the two radio buttons. This
function will be called when one of the radio buttons is clicked by mouse. For the check box, associating
bitmap with it is relatively simple, so it is implemented within the message handler. Besides this, a new
Boolean type variable CBtnDlg::m_bBmpCheck is declared to indicate the current state of the check box, and
an unsigned integer CBtnDlg::m_uBmpRadio is declared to indicate which radio button is being selected.
For each button, WM_COMMAND message handler is added through using Class Wizard. These message
handlers are CBtnDlg::OnBmpCheck(), CBtnDlg::OnBmpRadioA() and CBtnDlg::OnBmpRadioB()
respectively. The following code fragment shows the new members added to the class:
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