Linking Controls with Properties

Now that the property page has controls for displaying and modifying properties, the controls need to be linked to the properties. You can link controls in the property page with properties by using a shortcut to the Add Member Variable dialog box in ClassWizard.

To link the property page controls to properties

1. In the ResourceView pane, open the Circ project folder.
   
   
2. Open the Dialog folder.
   
   
3. Open the IDD_PROPPAGE_CIRC entry in the Dialog folder to load the property page template.
   
   
4. While holding down the CTRL key, double-click the edit box control for the Caption property.

   The Add Member Variable dialog box of ClassWizard appears.

5. After the m_ that is already in the Member variable name edit control, type caption, so the edit control contains m_caption.
   
   
6. In the Category drop-down list box, click Value.
   
   
7. In the Variable type drop-down list box, click CString.
   
   
8. In the Optional property name drop-down combo box, click Caption.
   
   
9. Click OK to close the Add Member Variable dialog box.

   If you were to open ClassWizard, the Member Variables tab would contain the new member variable mapping for the Caption property, as shown below:

   Control IDs:                 Type      Member
   IDC_CAPTION                  CString   m_caption
   IDC_CIRCLEOFFSET
   IDC_CIRCLESHAPE
   

10. Repeat steps 4 through 9, holding down the CTRL key and double-clicking the edit box control for the CircleOffset property, and entering the following values in the controls:

    Member variable name: m_circleOffset

    Category: Value

    Variable type: int

    Optional property name: CircleOffset

11. Repeat steps 4 through 9, holding down the CTRL key and double-clicking the check box for the CircleShape property, and entering the following values in the controls:

    Member variable name: m_circleShape

    Category: Value

    Variable type: BOOL

    Optional property name: CircleShape

    If you were to open ClassWizard, the Member Variables tab would contain the new member variable mapping for the CircleShape property, as shown below:

    Control IDs:                 Type      Member
    IDC_CAPTION                  CString   m_caption
    IDC_CIRCLEOFFSET             int       m_circleOffset
    IDC_CIRCLESHAPE              BOOL      m_circleShape
    

ClassWizard adds the member variables to the CCircPropPage class. ClassWizard also adds functions to the CCircPropPage class to initialize the member variables and to handle the exchange of data between the dialog controls, the member variables, and the properties.

The m_caption, m_circleOffset, and m_circleShape member variables are declared in CIRCPPG.H:

class CCircPropPage : public COlePropertyPage
{
    ...
    //{{AFX_DATA(CCircPropPage)
    ...
    CString m_caption;
    int m_circleOffset;
    BOOL m_circleShape;
    //}}AFX_DATA
    ...
};

The member variables are initialized in the constructor for the CCircPropPage class, the CCircPropPage function in CIRCPPG.CPP:

CCircPropPage::CCircPropPage() :
    COlePropertyPage(IDD, IDS_CIRCCTRL_PPG_CAPTION)
{
    //{{AFX_DATA_INIT(CCircPropPage)
    m_caption = _T("");
    m_circleOffset = 0;
    m_circleShape = FALSE;
    //}}AFX_DATA_INIT
}

Notice that strings assigned to member variables are first passed through the _T macro. This is the same macro used for string parameters to PX_ functions in CCircCtrl::DoPropExchange. The _T macro is used to maintain compatibility between different string representations, and it must be used for all literal strings in an ActiveX control project.

Data transfer is handled by the DDP_ and DDX_ macros in the DoDataExchange function in CIRCPPG.CPP:

void CCircPropPage::DoDataExchange(CDataExchange* pDX)
{
    //{{AFX_DATA_MAP(CCircPropPage)
    DDP_Text(pDX, IDC_CAPTION, m_caption, _T("Caption"));
    DDX_Text(pDX, IDC_CAPTION, m_caption);
    DDP_Text(pDX, IDC_CIRCLEOFFSET, m_circleOffset, _T("CircleOffset"));
    DDX_Text(pDX, IDC_CIRCLEOFFSET, m_circleOffset);
    DDP_Check(pDX, IDC_CIRCLESHAPE, m_circleShape, _T("CircleShape"));
    DDX_Check(pDX, IDC_CIRCLESHAPE, m_circleShape);
    //}}AFX_DATA_MAP
    DDP_PostProcessing(pDX);
}

The DDX_ macros are the same macros used for standard MFC dialog boxes. They synchronize dialog controls with dialog member variables. The DDP_macros are used only in ActiveX control property pages. They synchronize property page dialog member variables with specific control properties. Translations between an edit control and a short value and between a check box and a BOOL value are automatic. Similar to strings assigned to member variables, strings passed as parameters to DDP_ macros are first passed through the _T macro.

The Circle control now has a general property page that can be used to display and modify the values of several of its properties. The IDC_CAPTION edit control, IDC_CIRCLEOFFSET edit control, and IDC_CIRCLESHAPE check box are linked through property page member variables to the Caption, CircleOffset, and CircleShape properties, respectively. Between the default property page added in this lesson and the stock color and font property pages added earlier, all Circle control properties can now be accessed through property pages.