Dodataexchange (cdataexchange * PDX)

 

Dodataexchange (cdataexchange * PDX) is an important function of MFC cwnd.

In this function, you can use a series of ddx_xxxx (...) functions to implement data interaction between the UI and data, and use ddv_xxx (...) for data verification. For example:

// Simple text operations

Void

Afxapi
Ddx_text (cdataexchange *
PDX, int NIDC,
Byte & value); // special control types

Void

Afxapi
Ddx_check (cdataexchange *
PDX, int NIDC,
Int & value );

// Number of characters

Void

Afxapi
Ddv_maxchars (cdataexchange *
PDX, cstring
Const & value,
Int nchars );

....

These DDV may not meet our needs. However, you can use the cdataexchange parameter PDX to verify your data in dodataexchange. Use PDX-> m_bsaveandvalidate to determine whether updatedata (true) or updatedata (false ). If the verification fails, PDX-> fail () is triggered.

// Cdataexchange-for data exchange and validation

Class

Cdataexchange

{

// Attributes

Public

 

: Bool
M_bsaveandvalidate;
// True => Save and validate data

 

// Operations (for implementors of DDX and DDV procs)

Cwnd *
M_pdlgwnd;
// Container usually a dialog

 

 

 

Hwnd
Preparectrl (int
NIDC );
Hwnd
Prepareeditctrl (int
NIDC );
Void
Fail ();
// Will throw exception

 

Cdataexchange (cwnd *
Pdlgwnd,
Bool
Bsaveandvalidate );

 

Colecontrolsite *
Prepareolectrl (int
NIDC );
// For OLE controls in Dialog

// Implementation

 

Uint
M_idlastcontrol;
// Last control used (for validation)

 

Bool
M_beditlastcontrol;
// Last control was an edit item

};

It is worth noting that the preparexxx function. When data verification fails, the focus can be restored to the failed control. The custom data verification function can have the following structure:

Template <class T>

Void ddv_myvalidate (cdataexchange *
PDX, uint nctrlid, T & Data ...)

{

PDX-> preparectrl (nctrlid );

If (PDX-> m_bsaveandvalidate)

{

Bool bvalid = .....;

If (! Bvalid)

PDX-> fail ();

Else

Data =...; // get data from UI

}

Else

{

// Set data to contorl

}

}

 

Dodataexchange (cdataexchange * PDX) is an important function of MFC cwnd.

In this function, you can use a series of ddx_xxxx (...) functions to implement data interaction between the UI and data, and use ddv_xxx (...) for data verification. For example:

// Simple text operations

Void

Afxapi
Ddx_text (cdataexchange *
PDX, int NIDC,
Byte & value); // special control types

Void

Afxapi
Ddx_check (cdataexchange *
PDX, int NIDC,
Int & value );

// Number of characters

Void

Afxapi
Ddv_maxchars (cdataexchange *
PDX, cstring
Const & value,
Int nchars );

....

These DDV may not meet our needs. However, you can use the cdataexchange parameter PDX to verify your data in dodataexchange. Use PDX-> m_bsaveandvalidate to determine whether updatedata (true) or updatedata (false ). If the verification fails, PDX-> fail () is triggered.

// Cdataexchange-for data exchange and validation

Class

Cdataexchange

{

// Attributes

Public

 

: Bool
M_bsaveandvalidate;
// True => Save and validate data

 

// Operations (for implementors of DDX and DDV procs)

Cwnd *
M_pdlgwnd;
// Container usually a dialog

 

 

 

Hwnd
Preparectrl (int
NIDC );
Hwnd
Prepareeditctrl (int
NIDC );
Void
Fail ();
// Will throw exception

 

Cdataexchange (cwnd *
Pdlgwnd,
Bool
Bsaveandvalidate );

 

Colecontrolsite *
Prepareolectrl (int
NIDC );
// For OLE controls in Dialog

// Implementation

 

Uint
M_idlastcontrol;
// Last control used (for validation)

 

Bool
M_beditlastcontrol;
// Last control was an edit item

};

It is worth noting that the preparexxx function. When data verification fails, the focus can be restored to the failed control. The custom data verification function can have the following structure:

Template <class T>

Void ddv_myvalidate (cdataexchange *
PDX, uint nctrlid, T & Data ...)

{

PDX-> preparectrl (nctrlid );

If (PDX-> m_bsaveandvalidate)

{

Bool bvalid = .....;

If (! Bvalid)

PDX-> fail ();

Else

Data =...; // get data from UI

}

Else

{

// Set data to contorl

}

}