CMPT 212 Introduction to MFC and Windows Programming. Spring 2007

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1 CMPT 212 Introduction to MFC and Windows Programming Spring 2007

2 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

3 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 from the user

4 What Does This Mean to the Programmer? Flow of logic is no longer as explicit Need to design the system more carefully to ensure it always behaves in a graceful and reasonable manner no matter what the user does This applies to console applications as well, however since the user actions are typically less restricted in Windows applications this means the code has to handle more user actions appropriately

5 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

6 Event-Driven Programming in Windows (1 / 4) Done by using a message map: A message map is a mapping of possible actions(message identifiers) the user can do to message handlers - functions that handle the message appropriately The coder defines what messages the application should listen for and what message handlers to call

7 Event-Driven Programming in Windows (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

8 Event-Driven Programming in Windows (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()

9 Event-Driven Programming in Windows (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 menu selections We will come back to these in a bit

10 The Hungarian Notation Used to make variable names more explicit - prefix doubles with a d, classes with a C, etc Makes it easier to read the code (if you know what the prefixes mean, of course) The table on the right is from page 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

11 Creating an MFC Project in VC (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

12 Creating an MFC Project in VC (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

13 Creating an MFC Project in VC (3 / 4) The class that extends CWinApp is the one responsible for launching your application (it is the entry point) Typically it is very simple - it opens the main window and passes control to it You can do other initialization here such as setting up data structures

14 Creating an MFC Project in VC (4 / 4) Typically you will have a class that extends CFrameWnd, this is the class that is responsible for displaying a window In the simple example from the textbook, this class creates a window with a textbox in the center

15 Closer Look at the 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

16 Closer Look at the 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, with its top left corner at (100,100) and bottom right at (300,300) Just as in Java (0,0) is the top left corner, y-coordinate increases as you go down and x-coordinate increases as you go right

17 Closer Look at the 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 ; the other arguments are the window style (note the ORed flags), location, and owner In this particular case the style is child window, visible, with a border and with centered-text justification by default

18 Menus and Resources (1 / 4) When a menu item is selected it sends a programmerdefined 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, are reserved for windows messages They are then handled by adding appropriate entries to the message map

19 Menus and Resources (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 is received, the method Process(UINT id) is executed

20 Menus and Resources (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

21 Menus and Resources (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

22 Revisiting the Message Map (1 / 2) For the menu example, the map looks like this: BEGIN_MESSAGE_MAP(CMenusWin, CFrameWnd) ON_COMMAND(IDM_EXIT, OnExit) ON_COMMAND_RANGE(IDM_CHICKEN, END_MESSAGE_MAP() IDM_ROOTBEER, OnDoFood) Note the mapping from message identifier(s) to the message handler

23 Revisiting the Message Map (2 / 2) A small modification is required to the corresponding.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

24 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 does so by sending another message that is handled by the parent class, namely the close window message

25 ON_COMMAND_RANGE An example of how to use ON_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; }}

26 MFC Conventions for Message 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 as its sole argument

27 Dialog Boxes (1 / 3) Typically used to either get small pieces of information from the user (e.g. username / password) or to report progress / error to the user Are less flexible and simpler than regular windows To make a dialog box in MFC your class should extend CDialog (rather than CFrameWnd as before)

28 Dialog Boxes (2 / 3) Often dialog boxes are displayed as modal - while the dialog is open no other window of the 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 anything else until these are closed As you have probably guessed these should be used only when absolutely necessary

29 Dialog Boxes (3 / 3) Not very different in terms of code in comparison 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 overrides InitInstance())

30 CEdit and CButton Controls (1 / 3) The third example in the textbook introduces these two controls and uses them in a dialog CEdit is the basic edit text box (think JTextField, from Swing) CButton is the basic button (think JButton, from Swing)

31 CEdit and CButton Controls (2 / 3) Both inherit from CWnd, and as such support some common operations such as getting and setting the currently displayed text: GetWindowText(buffer, size); SetWindowText(buffer); Of course the way the text will be displayed is specific to the given component: Button simply displays the text Edit text box allows you modify this text by interacting with it

32 CEdit and CButton Controls (3 / 3) Having a look at the resource file (available in 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

33 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 or sprintf()) Not specific to MFC alone

34 Grabbing Controls from a Dialog (1 / 2) Allows to get a handle to a control inside the current dialog window Grab the IDC_NUMBER edit text box: CEdit *pnum = (CEdit *) (GetDlgItem(IDC_NUMBER)); Can also use the overloaded version on regular windows by passing it the pointer to the parent window as the first parameter, followed by the id

35 Grabbing Controls from a Dialog (2 / 2) Once you have the pointer to the control you can use it to manipulate the control: pnum->setwindowtext( "" ); // clear input pnum->setfocus(); // next input to Number This is handy, as you don t need to define a class member for every single control that you might need to access at some point in your code

Laboratory Exercise 11 Alternate (Intro to MFC)

Laboratory Exercise 11 Alternate (Intro to MFC) Topics: Microsoft Foundation Classes Goals: Upon successful completion of this lab you should be able to: 1. Write a simple winows program using the MFC