Advanced MFC Programming

Chapter 4. Button
Check here to
create bitmap
button
Figure 4-1. Change button’s style to “Owner draw”
Although every button has four states, we do not need to provide four bitmaps all the time. If one of
the bitmaps is not available, class CBitmapButton will draw the button’s corresponding state using the
default bitmap, which is the bitmap associated with button’s “up” state. So the bitmap used to represent a
button’s “up” state is required all the time and can not be omitted.
Automatic Method
We have two ways of associating bitmap images with different states of a bitmap button: we can either
let class CBitmapButton handle this automatically or we can do it manually. To use the automatic method,
the IDs of all four bitmap resources must be text strings, and must be formed by suffixing one of the
following four letters to the button’s caption text: ‘U’, ‘D’, ‘F’, ‘X’. These letters represent “up”, “down”,
“focused” and “disabled” state respectively. By naming the resource IDs this way, the rest thing we need to
do is calling function CBitmapButton::AutoLoad() in the dialog box’s initialization stage (within member
function CDialog::OnInitDialog()). Please note that we cannot call this function in the constructor of
class CDialog. At that time, the dialog box window is still not created (Therefore, the buttons are still not
available), and the bitmaps cannot be associated with the button correctly.
Sample
Sample 4.1\Btn demonstrates how to create bitmap button using automatic method. It is a dialog-based
application that is generated by the Application Wizard. First, the ID of default dialog template is changed
to IDD_DIALOG_BTN. Also, the “OK” and “Cancel” buttons originally included in the template are deleted.
Then a new button IDC_PLAY is added, whose caption text is set to “Play” (Figure 4-2). Since the button
will be drawn using the bitmaps, it doesn’t matter how big the button resource is. Besides this, we need to
set button’s style to “Owner draw”.
Set the button’s
caption text to
“Play”
Figure 4-2. Add a button in the dialog template to create bitmap button
Two bitmap resources are added to the application whose IDs are “PLAYU” and “PLAYD”
respectively (Figure 4-3). They correspond to button’s “up” and “down” states. In addition, the sizes of the
two bitmaps are exactly the same.
A CBitmapButton type variable is declared in class CBtnDlg to implement this bitmap button:
70