Introduction to MFC
Programming with Visual C++ Version 6.x
by Marshall Brain
MFC Styles
Controls are the user interface objects used to create interfaces
for Windows applications. Most Windows applications and dialog
boxes that you see are nothing but a collection of controls arranged
in a way that appropriately implements the functionality of the
program. In order to build effective applications, you must completely
understand how to use the controls available in Windows. There
are only six basic controls-CStatic, CButton , CEdit,
CList, CComboBox, and CScrollBar -along with
some minor variations (also note that Windows 95 added a collection
of about 15 enhanced controls as well). You need to understand
what each control can do, how you can tune its appearance and
behavior, and how to make the controls respond appropriately to
user events. By combining this knowledge with an understanding
of menus and dialogs you gain the ability to create any Windows
application that you can imagine. You can create controls either
programatically as shown in this tutorial, or through resource
files using the dialog resource editor. While the dialog editor
is much more convenient, it is extremely useful to have a general
understanding of controls that you gain by working with them programatically
as shown here and in the next tutorial.
The simplest of the controls, CStatic, displays static text. The CStatic class has no data members and only a few member functions: the constructor, the Create function for getting and setting icons on static controls, and several others. It does not respond to user events. Because of its simplicity, it is a good place to start learning about Windows controls.
In this tutorial we will look at the CStatic class to understand how controls can be modified and customized. In the following tutorial, we examine the CButton and CScrollBar classes to gain an understanding of event handling. Once you understand all of the controls and classes, you are ready to build complete applications.
A CStatic class in MFC displays static text messages to the user. These messages can serve purely informational purposes (for example, text in a message dialog that describes an error), or they can serve as small labels that identify other controls. Pull open a File Open dialog in any Windows application and you will find six text labels. Five of the labels identify the lists, text area, and check box and do not ever change. The sixth displays the current directory and changes each time the current directory changes.
CStatic objects have several other display formats. By changing the style of a label it can display itself as a solid rectangle, as a border, or as an icon. The rectangular solid and frame forms of the CStatic class allow you to visually group related interface elements and to add separators between controls.
A CStatic control is always a child window to some parent window. Typically, the parent window is a main window for an application or a dialog box. You create the static control, as discussed in Tutorial 2, with two lines of code:
CStatic *cs;
...
cs = new CStatic();
cs->Create("hello world",
WS_CHILD|WS_VISIBLE|SS_CENTER,
CRect(50,80, 150, 150),
this);
This two-line creation style is typical of all controls created using MFC. The call to new allocates memory for an instance of the CStatic class and, in the process, calls the constructor for the class. The constructor performs any initialization needed by the class. The Create function creates the control at the Windows level and puts it on the screen.
The Create function accepts up to five parameters, as described in the MFC help file. Choose the Search option in the Help menu of Visual C++ and then enter Create so that you can select CStatic::Create from the list. Alternatively, enter CStatic in the search dialog and then click the Members button on its overview page.
Most of these values are self-explanatory. The lpszText parameter specifies the text displayed by the label. The rect parameter controls the position, size, and shape of the text when it's displayed in its parent window. The upper left corner of the text is determined by the upper left corner of the rect parameter and its bounding rectangle is determined by the width and height of the rect parameter. The pParentWnd parameter indicates the parent of the CStatic control. The control will appear in the parent window, and the position of the control will be relative to the upper left corner of the client area of the parent. The nID parameter is an integer value used as a control ID by certain functions in the API. We'll see examples of this parameter in the next tutorial.
The dwStyle parameter is the most important parameter. It controls the appearance and behavior of the control. The following sections describe this parameter in detail.
All controls have a variety of display styles. Styles are determined at creation using the dwStyle parameter passed to the Create function. The style parameter is a bit mask that you build by or-ing together different mask constants. The constants available to a CStatic control can be found in the MFC help file (Find the page for the CStatic::Create function as described in the previous section, and click on the Static Control Styles link near the top of the page) and are also briefly described below:
These constants come from two different sources. The "SS" (Static Style) constants apply only to CStatic controls. The "WS" (Window Style) constants apply to all windows and are therefore defined in the CWnd object from which CStatic inherits its behavior. There are many other "WS" style constants defined in CWnd. They can be found by looking up the CWnd::Create function in the MFC documentation. The four above are the only ones that apply to a CStaticobject.
A CStatic object will always have at least two style constants or-ed together: WS_CHILD and WS_VISIBLE. The control is not created unless it is the child of another window, and it will be invisible unless WS_VISIBLE is specified. WS_DISABLED controls the label's response to events and, since a label has no sensitivity to events such as keystrokes or mouse clicks anyway, specifically disabling it is redundant.
All the other style attributes are optional and control the appearance of the label. By modifying the style attributes passed to the CStatic::Create function, you control how the static object appears on screen. You can learn quite a bit about the different styles by using style attributes to modify the text appearance of the CStatic object, as discussed in the next section.
The code shown below is useful for understanding the behavior of the CStatic object. It is similar to the listing discussed in Tutorial 2, but it modifies the creation of the CStatic object slightly. Please turn to Tutorial 1 for instructions on entering and compiling this code.
//static1.cpp
#include <afxwin.h>
// Declare the application class
class CTestApp : public CWinApp
{
public:
virtual BOOL InitInstance();
};
// Create an instance of the application class
CTestApp TestApp;
// Declare the main window class
class CTestWindow : public CFrameWnd
{
CStatic* cs;
public:
CTestWindow();
};
// The InitInstance function is called
// once when the application first executes
BOOL CTestApp::InitInstance()
{
m_pMainWnd = new CTestWindow();
m_pMainWnd->ShowWindow(m_nCmdShow);
m_pMainWnd->UpdateWindow();
return TRUE;
}
// The constructor for the window class
CTestWindow::CTestWindow()
{
CRect r;
// Create the window itself
Create(NULL,
"CStatic Tests",
WS_OVERLAPPEDWINDOW,
CRect(0,0,200,200));
// Get the size of the client rectangle
GetClientRect(&r);
r.InflateRect(-20,-20);
// Create a static label
cs = new CStatic();
cs->Create("hello world",
WS_CHILD|WS_VISIBLE|WS_BORDER|SS_CENTER,
r,
this);
}
The code of interest in listing 3.1 is in the function for the window constructor, which is repeated below with line numbers:
CTestWindow::CTestWindow()
{
CRect r;
// Create the window itself
1 Create(NULL,
"CStatic Tests",
WS_OVERLAPPEDWINDOW,
CRect(0,0,200,200));
// Get the size of the client rectangle
2 GetClientRect(&r);
3 r.InflateRect(-20,-20);
// Create a static label
4 cs = new CStatic();
5 cs->Create("hello world",
WS_CHILD|WS_VISIBLE|WS_BORDER|SS_CENTER,
r,
this);
}
The function first calls the CTestWindow::Create function for the window at line 1. This is the Create function for the CFrameWnd object, since CTestWindow inherits its behavior from CFrameWnd. The code in line 1 specifies that the window should have a size of 200 by 200 pixels and that the upper left corner of the window should be initially placed at location 0,0 on the screen. The constant rectDefault can replace the CRect parameter if desired.
At line 2, the code calls CTestWindow::GetClientRect, passing it the parameter &r. The GetClientRect function is inherited from the CWnd class (see the side-bar for search strategies to use when trying to look up functions in the Microsoft documentation). The variable r is of type CRect and is declared as a local variable at the beginning of the function.
Two questions arise here in trying to understand this code: 1) What does the GetClientRect function do? and 2) What does a CRect variable do? Let's start with question 1. When you look up the CWnd::GetClientRect function in the MFC documentation you find it returns a structure of type CRect that contains the size of the client rectangle of the particular window. It stores the structure at the address passed in as a parameter, in this case &r. That address should point to a location of type CRect. The CRect type is a class defined in MFC. It is a convenience class used to manage rectangles. If you look up the class in the MFC documentation, you will find that it defines over 30 member functions and operators to manipulate rectangles.
In our case, we want to center the words "Hello World" in the window. Therefore, we use GetClientRect to get the rectangle coordinates for the client area. In line 3 we then call CRect::InflateRect, which symmetrically increases or decreases the size of a rectangle (see also CRect::DeflateRect). Here we have decreased the rectangle by 20 pixels on all sides. Had we not, the border surrounding the label would have blended into the window frame, and we would not be able to see it.
The actual CStatic label is created in lines 4 and 5. The style attributes specify that the words displayed by the label should be centered and surrounded by a border. The size and position of the border is determined by the CRect parameter r .
By modifying the different style attributes you can gain an understanding of the different capabilities of the CStatic Object. For example, the code below contains a replacement for the CTestWindow constructor function in the first listing.
CTestWindow::CTestWindow()
{
CRect r;
// Create the window itself
Create(NULL,
"CStatic Tests",
WS_OVERLAPPEDWINDOW,
CRect(0,0,200,200));
// Get the size of the client rectangle
GetClientRect(&r);
r.InflateRect(-20,-20);
// Create a static label
cs = new CStatic();
cs->Create("Now is the time for all good men to \
come to the aid of their country",
WS_CHILD|WS_VISIBLE|WS_BORDER|SS_CENTER,
r,
this);
}
The code above is identical to the previous except the text string is much longer. As you can see when you run the code, the CStatic object has wrapped the text within the specified bounding rectangle and centered each line individually.
If the bounding rectangle is too small to contain all the lines of text, then the text is clipped as needed to make it fit the available space. This feature of the CStatic object can be demonstrated by decreasing the size of the rectangle or increasing the length of the string.
In all the code we have seen so far, the style SS_CENTER has been used to center the text. The CStatic object also allows for left or right justification. Left justification is created by replacing the SS_CENTER attribute with an SS_LEFT attribute. Right justification aligns the words to the right margin rather than the left and is specified with the SS_RIGHT attribute.
One other text attribute is available. It turns off the word wrap feature and is used often for simple labels that identify other controls (see figure 3.1 for an example). The SS_LEFTNOWORDWRAP style forces left justification and causes no wrapping to take place.
The CStatic object also supports two different rectangular display modes: solid filled rectangles and frames. You normally use these two styles to visually group other controls within a window. For example, you might place a black rectangular frame in a window to collect together several related editable areas. You can choose from six different styles when creating these rectangles: SS_BLACKFRAME, SS_BLACKRECT, SS_GRAYFRAME, SS_GRAYRECT, SS_WHITEFRAME, and SS_WHITERECT. The RECT form is a filled rectangle, while the FRAME form is a border. The color names are a little misleading-for example, SS_WHITERECT displays a rectangle of the same color as the window background. Although this color defaults to white, the user can change it with the Control Panel and the rectangle may not be actually white on some machines.
When a rectangle or frame attribute is specified, the CStatic 's text string is ignored. Typically an empty string is passed. Try using several of these styles in the previous code and observe the result.
You can change the font of a CStatic object by creating a CFont object. Doing so demonstrates how one MFC class can interact with another in certain cases to modify behavior of a control. The CFont class in MFC holds a single instance of a particular Windows font. For example, one instance of the CFont class might hold a Times font at 18 points while another might hold a Courier font at 10 points. You can modify the font used by a static label by calling the SetFont function that CStatic inherits from CWnd. The code below shows the code required to implement fonts.
CTestWindow::CTestWindow()
{
CRect r;
// Create the window itself
Create(NULL,
"CStatic Tests",
WS_OVERLAPPEDWINDOW,
CRect(0,0,200,200));
// Get the size of the client rectangle
GetClientRect(&r);
r.InflateRect(-20,-20);
// Create a static label
cs = new CStatic();
cs->Create("Hello World",
WS_CHILD|WS_VISIBLE|WS_BORDER|SS_CENTER,
r,
this);
// Create a new 36 point Arial font
font = new CFont;
font->CreateFont(36,0,0,0,700,0,0,0,
ANSI_CHARSET,OUT_DEFAULT_PRECIS,
CLIP_DEFAULT_PRECIS,
DEFAULT_QUALITY,
DEFAULT_PITCH|FF_DONTCARE,
"arial");
// Cause the label to use the new font
cs->SetFont(font);
}
The code above starts by creating the window and the CStatic object as usual. The code then creates an object of type CFont. The font variable should be declared as a data member in the CTestWindow class with the line "CFont *font". The CFont::CreateFont function has 15 parameters (see the MFC help file), but only three matter in most cases. For example, the 36 specifies the size of the font in points, the 700 specifies the density of the font (400 is "normal," 700 is "bold," and values can range from 1 to 1000. The constants FW_NORMAL and FW_BOLD have the same meanings. See the FW constants in the API help file), and the word "arial" names the font to use. Windows typically ships with five True Type fonts (Arial, Courier New, Symbol, Times New Roman, and Wingdings), and by sticking to one of these you can be fairly certain that the font will exist on just about any machine. If you specify a font name that is unknown to the system, then the CFont class will choose the default font seen in all the other examples used in this tutorial.
For more information on the CFont class see the MFC documentation. There is also a good overview on fonts in the API on-line help file. Search for "Fonts and Text Overview."
The SetFont function comes from the CWnd class. It sets the font of a window, in this case the CStatic child window. One question you may have at this point is, "How do I know which functions available in CWnd apply to the CStatic class?" You learn this by experience. Take half an hour one day and read through all the functions in CWnd . You will learn quite a bit and you should find many functions that allow you to customize controls. We will see other Set functions found in the CWnd class in the next tutorial.
In this tutorial we looked at the many different capabilities of the CStatic object. We left out some of the Set functions inherited from the CWnd class so they can be discussed in Tutorial 4 where they are more appropriate.
In Visual C++ Version 5.x, looking up functions that you are unfamiliar with is very simple. All of the MFC, SDK, Windows API, and C/C++ standard library functions have all been integrated into the same help system. If you are uncertain of where a function is defined or what syntax it uses, just use the Search option in the Help menu. All occurrences of the function are returned and you may look through them to select the help for the specific function that you desire.
This tutorial contains several different example programs. There are two different ways for you to compile and run them. The first way is to place each different program into its own directory and then create a new project for each one. Using this technique, you can compile each program separately and work with each executeable simultaneously or independently. The disadvantage of this approach is the amount of disk space it consumes.
The second approach involves creating a
single directory that contains all of the executables from this
tutorial. You then create a single project file in that directory.
To compile each program, you can edit the project and change its
source file. When you rebuild the project, the new executable
reflects the source file that you chose. This arrangement minimizes
disk consumption, and is generally preferred.