Document/View Example: Student Record

Windows NT Systems Programming: Spring 2000

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Document View Example: Student Records

This example illustrates the following features of document/view (source code here)

Form view
Explicit invocation of DDX functions (using UpdateData) - don't have OnOK inherited to do this for us.
Fix OnNewDocument handler
Add simple file save/open

Student Object

Data is kept in its own object, name and grade of student, no biggie here.
- Copy constructor
- Overload Assignment
- Overload "==" and "!=" comparison operators
- Override "Dump" for debugging (we will invoke in destructor we see the data)
```
#ifdef _DEBUG
void CStudent::Dump(CDumpContext& dc) const
{
    CObject::Dump(dc);
    dc << "m_strName = " << m_strName << "\nm_nGrade = " << m_nGrade;
}
#endif // _DEBUG
```

Will be a data member of the Document object

Document Object

Pretty tame here - but we will fix OnNewDocument which should reset the Student Object.

BOOL CEx16aDoc::OnNewDocument()
{
	if (!CDocument::OnNewDocument())
		return FALSE;

	// (SDI documents will reuse this document)
	m_student = CStudent("default value", 0);	// added to fix non reset on File/New

	return TRUE;
}

Why does assignment work?
Can remove initializer constructor in constructor - WHY

View Object

Derived from CFormView (like a dialog window as the main window) Useful for Data Entry applications.
Can design form with dialog editor.
Can use class wizard to set DDX functions for controls in window.
And Data Validation (e.g. grade must be numeric in range 0 to 100)

"OnInitialUpdate" called whenever there is a new document (start up, New, Open)

void CEx16aView::OnInitialUpdate()
{   // called on startup
    UpdateControlsFromDoc();
}

// all action is here

void CEx16aView::UpdateControlsFromDoc()
{   // called from OnInitialUpdate and OnEditClearAll
    CEx16aDoc* pDoc = GetDocument();
    m_nGrade = pDoc->m_student.m_nGrade;
    m_strName = pDoc->m_student.m_strName;
    UpdateData(FALSE); // calls DDX

}

Sets initial data in controls from data retrieved from the document

However, because don't have standard OnOk handling, need to control DDX invocation explicitely, as follows
```
void CEx16aView::OnEnter() 
{
    CEx16aDoc* pDoc = GetDocument();
    UpdateData(TRUE); 
    pDoc->m_student.m_nGrade = m_nGrade; 
    pDoc->m_student.m_strName = m_strName;
	
}
```
- UpdateData will call relevant DDX's, TRUE means data is being retrieved from control, otherwise the values in the controls are being set.
- remember the passage of this data is from CEdit window text to CEx16aView m_nGrade (using DDX and then validates using DDV) then we can save it in the document.

Adding File Save/Open

Add Serialize method to Student

void CStudent::Serialize(CArchive& ar)
{
	if (ar.IsStoring())
	{
		ar << m_strName <<  m_nGrade;
	}
	else
	{
		ar >> m_strName >> m_nGrade;
	}
}

Modify Serialize method of Document

void CEx16aDoc::Serialize(CArchive& ar)
{
	if (ar.IsStoring())
	{
		m_student.Serialize(ar);
	}
	else
	{
		m_student.Serialize(ar);
	}
}

Now can use Open/Save