MFC radio buttons - DDX_Radio and DDX_Control behavior

Question

I have an MFC dialog in which there are two radio buttons. I have put them in a nice group, their IDCs are one after each other (RB_LEFT, RB_RIGHT).

I want to use DDX_Radio so I can access the buttons using an integer value so in the function DoDataExchange I call :

DDX_Radio(pDX, RB_LEFT, mRBLeftRight);

where mRBLeftRight is a member variable of integer type. I also need to edit the buttons properties so I wanted to use a DDX_Control to map them on member variables mRBLeft and mRBRight (CButton):

DDX_Control(pDX, RB_LEFT, mRBLeft);
DDX_Control(pDX, RB_RIGHT, mRBRight);

Now if I do the call to DDX_Control, whenever DoDataExchange is called, the application crashes because DDX_Control forces RB_LEFT to handle a message that DDX_Radio cannot handle. This part I understand.

I decided to not use DDX_Control (removed the calls in DoDataExchange) and just keep a pointer to my radio buttons (CButton*) in my classes. So in my OnInitDialog function, I do the following calls :

mRBLeft= ((CButton*)GetDlgItem(RB_LEFT));
mRBRight = ((CButton*)GetDlgItem(RB_RIGHT));

Now as long as I don't use mRBLeft it's going to be fine, but if I do, bam, crash on DoDataExchange. The thing that really puzzles me is if I change my left radio button using ((CButton*)GetDlgItem(RB_LEFT)->SetCheck(true) it's going to work. Sooo what's the difference ?

(I know it's a lot of hassle for little, but I just wanna understand the mechanics)

I read somewhere that I shouldn't store a pointer returned from GetDlgItem, which is probably right, perhaps this is the cause of my problem? — levesque

Goz Goz · Accepted Answer · 2009-07-22T14:59:48

TBH Its even easier than JC's post leads you to believe.

DDX_Control( pDX, IDC_RADIO3, m_r3 );
DDX_Control( pDX, IDC_RADIO4, m_r4 );

m_Val   = 0;
DDX_Radio( pDX, IDC_RADIO3, m_Val );

You need to mark the FIRST radio button in the group with WS_GROUP (In this case IDC_RADIO3). You are now good to go and it will automatically select IDC_RADIO3).

Now to keep m_Val up to date it is probably worth putting a click handler on all the radio buttons in the group. Inside that function, simply, call UpdateData( TRUE ); m_Val will now point to the index of the radio button in the group.

MFC radio buttons - DDX_Radio and DDX_Control behavior

2 Answers