Document and View architecture

Document and View Architecture:

1.     Concept of document and view architecture:

The document and view architecture consists of three parts. The view, one or more document and frames.

i.                    View:

The base class for view is CView. The view is platform on which the user can view the stored data and he can edit that data.

ii.                  Document:

The base class document is CDocument. The document is like a buffer which simply stores all the user data or the file is saved on disk. This saved file is called document.

iii.                Frame:

The base class for frame is CFrameWnd. This frame is physical representation of windows. The frame provides the border to the window.

2.     Menu:

Menu bar is an important element of any GUI. It is basically a collection of various menu items. These items can be arranged on the pop-up menu. User can select any item by clicking the top level items first then by selecting the desired menu option. In Microsoft VC++ there is a menu resource using which the menu can be created.

 Ex:

Steps for creating Menu:

i.                    Create new project using MFC AppWizard

ii.                  Goto Resource view

iii.                Goto Menu option in the list

iv.               Now default Menu will be shown in main window. We can add new item by clicking on last blank box icon

3.     Keyboard Accelerators:

We have to make use of keyboard while using shortcut key. Sometime one character is underlined; it indicates that press that character along with the special key and that particular menu item will be selected. Such underlined characters are hotkeys.

Some application designer may use of keyboard accelerator. Keyboard accelerators are similar to the hot key for example in Microsoft word, the short key F7 is used for spell check-up.

Steps for creating Menu:

i.                    Create new project using MFC AppWizard

ii.                  Goto Resource view

iii.                Goto Accelerator option in the list

iv.               Now a list of all already constructed accelerators will be shown in main window. We can add new accelerator by right clicking on any already defined accelerator and selecting New Accelerator option.

4.     Tool Bar:

A tool bar consists of horizontal arrangement of graphical button, the graphical image for buttons are stored in a single bitmap that is attached to single resource file. When a button is clicked, it sends a command message.

Ex:

Steps for creating toolbar:

i.                    Create new project using MFC AppWizard

ii.                  Goto Resource view

iii.                Goto Toolbar option in the list

iv.               Now a Toolbar will be shown in main window. We can add new item by clicking on last blank box icon

Tool tips & prompt string:

We can set the prompt string by writing some string in the prompt window of particular menu item properties. The prompt string can be displayed in the status bar window.

If we want to get tool tips displayed on each button on the toolbar then that tool tip can be set by adding the tip’s text to the end of menu prompt, preceded by a new line character (\n).

5.     Status Bar:

The status bar is another child window which is present at the bottom of the main window. This window neither accepts input nor generates any command, but used to display the help information.

The status bar is made up of two types of panes –

                                           I.            Message line panes:

On the message line pane the help information can be displayed.

                                         II.            Indicator panes:

The indicator panes show current status of key, such as caps lock, num lock, scroll lock is indicated.

In the mainFRM.CPP file the framework for status bar can be defined as follows:

Static UINT indicators[]={ ID_Seprator, ID_INDICATOR_CAPS, ID_INDICATOR_NUM, ID_INDICATOR_SCRL}

Class Wizard for status message –

6.     Reusable frame window Base class:

Any mainframe of window is derived from the class CframeWnd. The reusable frame is kind of window frame that is derived from CframeWnd Class.

But it remember following characteristics of the frame window –

a.     Window size

b.     Window position

c.      Window status (Minimized| Maximized)

d.     Toolbar & Status bar  getting enable & disable

7.     Separating document from its view:

In the document view architecture the document object hold data and the view object display the data of the user and allow him to edit that data. In SDI application there are two Base classes CDocument & CView.

                                           I.            CView::GetDocument():

Every view object is associated with only one document.

The GetDocument() function allow moving the control from view to document. Sometimes on running the application, user enter the data in the edit box that means the data is updated in view mode and this data must be updated by the document object as well.

                                         II.            CDocument::OnNewDocument();

The document framework first construct the document object & when user click new menu item from the file then the OnNewDocument() function is called. We can set some initial data for viewing on this new document function.

                                      III.            CDocument::UpdateAllView():

The UpdateAllView() function must be called when the data in the document gets change and document must inform it to one or more view associated with it.

                                      IV.            CView::OnInitialUpdate():

When an application gets standard or when user click the new from file menu or when user clicks on the open from the file menu, the CView function is called at that time OnInitialUpdate () is called.

                                        V.            CView::OnUpdate():

The base class CView calls the OnInitialUpdate() function which in turn , calls OnUpdate() function. The purpose of this function is to update all the view if any change occur in the document data.