Page 207 - DCAP408_WEB_PROGRAMMING

Unit 12: Dialog Boxes (II)

The Data Exchange and Validation Mechanism Notes

The DoDataExchange() function is called several times during the lifetime of a dialog box and
performs a variety of tasks. When the dialog box is initialized, this function subclasses any
mapped controls through the DDX_Control routine (discussed in more detail later in the section,
"Initializing the Dialog Box Controls"). Then it transfers the data held in the member variables
to the controls using the DDX_ routines. Finally, after the user clicks OK, the data from the
controls is validated using DDV_ routines and then transferred back into the member variables
using the DDX_ routines again.
You'll notice that the DoDataExchange() function is passed a pointer to a CDataExchange object.
This object holds the details that let the DDX routines know whether they should be transferring
data to or from the controls. The DDX_ routines then implement the Windows message required
to set or retrieve data from the control associated with the given control ID.

When the m_bSaveAndValidate member is set to TRUE, the data exchange should transfer data
from the controls to the member variables and perform validation. It is set to FALSE when data
from the member variables should be loaded into the controls. You can add your own custom
code to DoDataExchange() to transfer data to or from the controls and check the
m_bSaveAndValidatemember of the CDataExchange object to see whether you should be
transferring the data to or from the control.

12.4 Modal, Modeless and System Modal Dialog boxes

Dialog boxes are specifically used for accepting input from the user or displaying a message to
the user. Windows operating system comes with default dialog boxes like Font dialog box,
Printer dialog box, Color dialog box etc. Most of the applications specially those vendored by
Microsoft borrow these dialog boxes from Windows whenever they need. There are three kinds
of dialog boxes.

1. Modal Dialog Box (Application Modal Dialog Box)
2. Modeless Dialog Box
3. System Modal Dialog Box

12.4.1 Modal Dialog Box

Modal dialog boxes can be also called as Application Modal dialog box. These dialog boxes
insist you to respond to them before continuing in the same application. A Modal dialog box
while in action, stops running your code until it is closed or hidden. Although, you can call
default Dialog box as a Modal dialog box, but you can also create of your own. The Show method
of form uses VbModal style to load the form as a Modal dialog box. The general syntax you
follow will be :FormName.Show VbModal

12.4.2 Modeless Dialog Box

Modeless dialog boxes do not need to be closed to loose their focus. They are just like any other
form in your application and loose their focus as soon as you click some other Window outside
the application.

Example: A Find and Replace dialog box, Document Windows in Word application are
few examples of Modeless dialog boxes.

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