CMPT 212Introduction to MFC andWindows Programming

Spring 2007

What is MFC?

MFC: Microsoft Foundation Classes MFC is a framework built on top of standard

windows C++ libraries Provides the user with a number of classes

that make windows programming easier

Windows Programming Based on event-driven architecture Console applications - the program tells (“drives”)

the user when and what to enter Windows applications - the user “drives” the

program by interacting with it The program thus interacts with the user by

handling events and waiting for new events fromthe user

What Does This Mean to theProgrammer? Flow of logic is no longer as explicit Need to design the system more carefully to ensure

it always behaves in a graceful and reasonablemanner no matter what the user does This applies to console applications as well, however since

the user actions are typically less restricted in Windowsapplications this means the code has to handle more useractions appropriately

MFC versus Swing The obvious difference - MFC is for Win32 C++, Swing is for

Java MFC is an abstraction / improvement of Win32 GUI

programming Swing is an abstraction / improvement of AWT Swing is considerably younger than MFC, and as such is

easier to use and is more elegant Swing has listeners, MFC has message maps

One of the reasons why MFC is uglier / trickier MFC has its own “resource definition language”; Swing does

not

Event-Driven Programming inWindows (1 / 4) Done by using a message map:

A message map is a mapping of possibleactions(message identifiers) the user can do to messagehandlers - functions that handle the messageappropriately

The coder defines what messages the applicationshould listen for and what message handlers to call

Event-Driven Programming inWindows (2 / 4) Does the coder have to handle all types of

messages? No, Windows provides default message handlers for all

standard message identifiers (for the particular objects,like windows)

User can override this behavior Coders can also define their own message

identifiers and the corresponding message handlers

Event-Driven Programming inWindows (3 / 4) A message map looks like so:

BEGIN_MESSAGE_MAP(ownerClassName, baseClassName)…// Mappings go here

END_MESSAGE_MAP()

A default mapping:ON_WM_PAINT() // Calls OnPaint()

A custom mapping:ON_COMMAND(ID, foo) // Calls foo()

Event-Driven Programming inWindows (4 / 4) When to override default message handlers (such

as OnPaint())? When you want to provide different functionality, such as

your own way to paint a window ON_COMMAND(), used with user-defined message

identifiers, is commonly used for handling menuselections

We will come back to these in a bit

The Hungarian Notation Used to make variable names

more explicit - prefix doubleswith a ‘d’, classes with a ‘C’,etc

Makes it easier to read thecode (if you know what theprefixes mean, of course)

The table on the right is frompage 32 of your MFC textbook

ar - array b - BOOL/bool c - char C - class d - double l - long lp - long pointer m_ - class member variable n or i - integer p - pointer s - string sz - string with null termination s_ - static class member

Creating an MFC Project inVC++ 6.0 (1 / 4) Select “File -> New…” from the menu Click on the “Projects” tab Select “Win32 Application” and fill in the project

name / location Do not use Wizards, select “An empty project” on

the next screen and click “Finish”

Creating an MFC Project inVC++ 6.0 (2 / 4) Add a .h and a .cpp file As usual, your .h file should contain the specification and

.cpp the implementation Enable MFC (Project -> Settings -> General -> Microsoft

Foundation Classes -> Use MFC in a Shared DLL) In your .cpp, #include <afxwin.h> Code your program, extending existing MFC classes such as

CFrameWnd and CWinApp

Creating an MFC Project inVC++ 6.0 (3 / 4) The class that extends CWinApp is the one

responsible for launching your application (it is theentry point)

Typically it is very simple - it opens the mainwindow and passes control to it

You can do other initialization here such as settingup data structures

Creating an MFC Project inVC++ 6.0 (4 / 4) Typically you will have a class that extends

CFrameWnd, this is the class that is responsible fordisplaying a window

In the simple example from the textbook, this classcreates a window with a textbox in the center

Closer Look atthe Example (1 / 3)BOOL InitInstance() {

m_pMainWnd = new CWelcomeWindow();

m_pMainWnd->ShowWindow( m_nCmdShow );

m_pMainWnd->UpdateWindow();

return TRUE;

}

Overrides the default InitInstance() from CWinApp Creates a new window, displays and updates it Returns TRUE to signify success of initialization

Closer Look atthe Example (2 / 3) Create(NULL, "Welcome", WS_OVERLAPPEDWINDOW,

CRect(100, 100, 300, 300)); Creates a standard window (the NULL and the

WS_OVERLAPPEDWINDOW flag) with title “Welcome”, withits top left corner at (100,100) and bottom right at (300,300)

Just as in Java (0,0) is the top left corner, y-coordinateincreases as you go down and x-coordinate increases as yougo right

Closer Look atthe Example (3 / 3) m_pGreeting->Create("Welcome to Visual C++

with MFC!", WS_CHILD | WS_VISIBLE |WS_BORDER | SS_CENTER, CRect( 40, 50, 160,100 ), this);

Creates the window holding the text “Welcome to …”; theother arguments are the window style (note the ORed flags),location, and owner

In this particular case the style is child window, visible, with aborder and with centered-text justification by default

Menus andResources (1 / 4) When a menu item is selected it sends a programmer-

defined message These messages are typically prefixed with “IDM_” (M for menu) Need to be defined somewhere Defined as macros using #define, not const Programmer-defined messages should have values between

1024 and 65545, 0 - 1023 are reserved for windows messages They are then handled by adding appropriate entries to the

message map

Menus andResources (2 / 4) To handle a particular message the programmer

should add the following to the message map:ON_COMMAND(IDM_MSGID, DoSomething); When the message with id IDM_MSGID is received, the

method DoSomething() is executed Can also handle a range of messages:

ON_COMMAND_RANGE(START, END, Process);

When the message with id between START and END isreceived, the method Process(UINT id) is executed

Menus andResources (3 / 4) Defining a menu:

Can either write the resource file by hand or use the VC++IDE interface

Looking at the source of the resource file:Food MENU{

POPUP "File"

{MENUITEM "Exit", IDM_EXIT}

…} Defines the “Exit” item of the “File” menu and assigns it

IDM_EXIT id

Menus andResources (4 / 4) A menu with two items:

POPUP "Beverage"{

MENUITEM "Ginger Ale", IDM_GINGERALE

MENUITEM "Root Beer", IDM_ROOTBEER

}

Similarly, creates a “Beverage” menu with items “Ginger Ale”and “Root Beer” with corresponding IDs

A single resource file may contain more than one menu Resource files are written in resource definition language that is

actually not C++ More on resources later

Revisiting theMessage Map (1 / 2)

For the menu example, the map looks likethis:BEGIN_MESSAGE_MAP(CMenusWin, CFrameWnd)

ON_COMMAND(IDM_EXIT, OnExit)

ON_COMMAND_RANGE(IDM_CHICKEN,

IDM_ROOTBEER, OnDoFood)

…

END_MESSAGE_MAP()

Note the mapping from message identifier(s) tothe message handler

Revisiting theMessage Map (2 / 2)

A small modification is required to thecorresponding .h: Need to add DECLARE_MESSAGE_MAP() to the

end of the class declaration This refers to the message map in the .cpp file Why?

MFC preprocessor “magic”

ON_COMMAND

An example of how to use ON_COMMAND:afx_msg void CMenusWin::OnExit()

{

SendMessage(WM_CLOSE);

}

This particular example exits the program. It doesso by sending another message that is handledby the parent class, namely the “close window”message

ON_COMMAND_RANGE

An example of how to useON_COMMAND_RANGE:afx_msg void CMenusWin::OnDoFood(UINT nFood) {

switch (nFood){case IDM_CHICKEN: tally(m_nChicken, 2.25); break;case IDM_FISH: tally(m_nFish, 1.80); break;…}}

MFC Conventions forMessage Handlers

Prefixed with afx_msg Begin with “On” and followed by the

message type (e.g. “Exit”) No parameters, return type is void For ON_COMMAND_RANGE, as we’ve just

seen, takes in a single unsigned integer asits sole argument

Dialog Boxes (1 / 3)

Typically used to either get small pieces ofinformation from the user (e.g. username /password) or to report progress / error to theuser

Are less flexible and simpler than regularwindows

To make a dialog box in MFC your classshould extend CDialog (rather thanCFrameWnd as before)

Dialog Boxes (2 / 3)

Often dialog boxes are displayed as modal -while the dialog is open no other window ofthe particular application can gain focus This is referred to as application modal In some special applications you might encounter

system modal dialogs - you cannot do anythingelse until these are closed As you have probably guessed these should be used

only when absolutely necessary

Dialog Boxes (3 / 3)

Not very different in terms of code incomparison to windows: Inherit CDialog (instead of CFrameWnd) Define a message map and the necessary ids /

handlers Define an entry point as before (a class that

inherits from CWinApp and overridesInitInstance())

CEdit and CButtonControls (1 / 3)

The third example in the textbook introducesthese two controls and uses them in a dialog

CEdit is the basic edit text box (thinkJTextField, from Swing)

CButton is the basic button (think JButton,from Swing)

CEdit and CButtonControls (2 / 3) Both inherit from CWnd, and as such support some

common operations such as getting and setting thecurrently displayed text: GetWindowText(buffer, size);

SetWindowText(buffer);

Of course the way the text will be displayed isspecific to the given component: Button simply displays the text Edit text box allows you modify this text by interacting with

it

CEdit and CButtonControls (3 / 3)

Having a look at the resource file (availablein the book / online) we see that: IDC_NUMBER is an edit text box that supports

numbers only IDC_ADD is a default button for this dialog IDC_TOTAL is a read-only edit text box that does

not have a tab-stop IDC_CLEAR is a regular button that does not

have a tab-stop

itoa() and atoi() These two functions have a very simple

purpose Translate from an integer to a C-style string (itoa

= int to “string”) Translate from a C-style string to an integer (atoi

= “string” to int) Handy for quick conversions, but not hard to

write your own (e.g. using stringstream orsprintf())

Not specific to MFC alone

Grabbing Controlsfrom a Dialog (1 / 2)

Allows to get a handle to a control inside thecurrent dialog window Grab the IDC_NUMBER edit text box: CEdit *pNum = (CEdit *) (GetDlgItem(IDC_NUMBER));

Can also use the overloaded version onregular windows by passing it the pointer tothe parent window as the first parameter,followed by the id

Grabbing Controlsfrom a Dialog (2 / 2)

Once you have the pointer to the control youcan use it to manipulate the control:pNum->SetWindowText( "" ); // clear inputpNum->SetFocus(); // next input to Number

This is handy, as you don’t need to define aclass member for every single control thatyou might need to access at some point inyour code