ch11.htm

Visual C++ 6.0 21天自学教程 一本适合初学和对c++有一定基础的人学习的好书

	<P>
	<DT></DT>
	<DD><B>5. </B>Search for the line BEGIN_MESSAGE_MAP and add the lines in Listing
	11.2 just after it. It's important that this code be between the BEGIN_MESSAGE_MAP
	line and the //{{AFX_MSG_MAP line. If these commands are between the //{{AFX_MSG_MAP
	and //}}AFX_MSG_MAP lines, then the Class Wizard will remove or corrupt them.
	<P>
</DL>

<H4>LISTING 11.2. THE EVENT-HANDLER MESSAGE MAP ENTRIES IN Day11Doc.cpp.</H4>
<PRE> 1: //////////////////////////////////////////////////////////////////////
 2: // CDay11Doc
 3: 
 4: IMPLEMENT_DYNCREATE(CDay11Doc, CDocument)
 5: 
 6: BEGIN_MESSAGE_MAP(CDay11Doc, CDocument)
 7:     ON_COMMAND_RANGE(ID_COLOR_BLACK, ID_COLOR_WHITE, OnColorCommand)
 8:     ON_UPDATE_COMMAND_UI_RANGE(ID_COLOR_BLACK, ID_COLOR_WHITE, &Acirc;OnUpdateColorUI)
 9:     //{{AFX_MSG_MAP(CDay11Doc)
10:         // NOTE - the ClassWizard will add and remove mapping macros &Acirc;here.
11:         //    DO NOT EDIT what you see in these blocks of generated &Acirc;code!
12:     //}}AFX_MSG_MAP
13: END_MESSAGE_MAP()
14: 
15: const COLORREF CDay11Doc::m_crColors[8] = {
16:     RGB(   0,   0,   0),    // Black
17:     RGB(   0,   0, 255),    // Blue
18: .
19: .
</PRE>

<PRE>20: .</PRE>
<P>

<DL>
	<DT></DT>
	<DD><B>6. </B>Scroll to the bottom of the file and add the two event message handler
	functions in Listing 11.3.
	<P>
</DL>

<H4>LISTING 11.3. THE COLOR MENU EVENT-HANDLER FUNCTIONS.</H4>
<PRE> 1: void CDay11Doc::OnColorCommand(UINT nID)
 2: {
 3:     // Set the current color
 4:     m_nColor = nID - ID_COLOR_BLACK;
 5: }
 6: 
 7: void CDay11Doc::OnUpdateColorUI(CCmdUI* pCmdUI)
 8: {
 9:     // Determine if the menu entry should be checked
10:     pCmdUI-&gt;SetCheck(GetColor() == pCmdUI-&gt;m_nID ? 1 : 0);
</PRE>

<PRE>11: }</PRE>
<P>In Listing 11.1, the two function declarations that you added are specified as
event message handlers by the afx_msg function type declarations. These type of function
declarations need to have protected access. Otherwise, they are virtually identical
to any other class member function declaration.</P>
<P>In Listing 11.2, the two message map entries, ON_COMMAND_RANGE and ON_UPDATE_COMMAND_UI_RANGE,
are standard message map entries, but the Class Wizard does not support or understand
them. If you examine the message map entries from the previous day's applications,
you will notice that there are ON_COMMAND and ON_UPDATE_COMMAND_UI message map entries.
These macros have two arguments, the message ID and the event-handler function name
that should be called for the event message. These new message map entries function
in the same way, but they have two event ID arguments instead of one. The two event
ID arguments mark the two ends of a range of event IDs that should be passed to the
function specified. These two event IDs should be the first and last menu entries
you created when building the color menu.</P>


<BLOCKQUOTE>
	<P>
<HR>
<STRONG>NOTE:</STRONG> The message map is a mechanism used by Visual C++ and MFC to easily
	specify event messages and the functions that should be called to handle the event.
	These message-map commands are converted by the Visual C++ compiler into a fast and
	efficient map for calling the appropriate event functions when a message is received
	by the application. Whenever you add a function through the Class Wizard, you are
	not only adding the function to the code, but you are also adding an entry into the
	message map for that class.
<HR>


</BLOCKQUOTE>

<P>When you use the ON_COMMAND_RANGE message-map entry, the event message ID is automatically
passed as an argument to the event-handler function. This allows you to create the
function in Listing 11.3 to handle the color selection event messages. If you compile
and run your application at this point, you should find that the color selection
functionality is all working just as it did yesterday, as shown in Figure 11.3.</P>
<P><A HREF="javascript:popUp('11fig03.gif')"><B>FIGURE 11.3.</B></A><B> </B><I>Running
the MDI application.</I></P>

<P><I></I>
<H2><A NAME="Heading6"></A>Adding a Context Menu</H2>
<P>In most Windows applications, you can right-click the mouse and what is known
as a context menu, or pop-up menu, appears. Back on Day 6, &quot;Creating Menus for
Your Application,&quot; you implemented a simple pop-up menu. However, there is a
mechanism for creating and using these context menus when Windows thinks that the
menu should be opened. This process allows you to add context menus that behave more
consistently with other Windows applications (and if Microsoft changes how the context
menus are triggered with a new version of Windows, yours will still behave according
to the Windows standard).</P>
<P>An event message WM_CONTEXTMENU is passed to the event queue when the right mouse
button is released or when the context menu button is pressed (if you have a newer
Windows-enabled keyboard with the context menu button). If you place an event-handler
function on the WM_CONTEXTMENU event message, you can display a pop-up menu with
confidence that you are showing it at the appropriate time.</P>
<P>To add the context menu to your application, you create a new menu for use as
the context menu. To do this, follow these steps:</P>
<P>

<DL>
	<DT></DT>
	<DD><B>1. </B>In the Resource View tab on the workspace pane, right-click the Menu
	folder.
	<P>
	<DT></DT>
	<DD><B>2. </B>Select Insert Menu from the pop-up menu (or should I say context menu).
	<P>
	<DT></DT>
	<DD><B>3. </B>Select the new menu (still in the workspace pane), open its properties
	dialog, and name the menu IDR_CONTEXTMENU.
	<P>
	<DT></DT>
	<DD><B>4. </B>In the Menu Designer, specify the top-level menu caption as a single
	space. This causes Visual C++ to add the first entry in the drop-down portion of
	the menu.
	<P>
	<DT></DT>
	<DD><B>5. </B>In the first drop-down menu entry, specify the caption as &amp;Width
	and check the Pop-up check box. (This causes the ID combo box to be disabled and
	an arrow to display beside the caption, along with another menu entry to the right
	of the menu entry you are modifying.)
	<P>
	<DT></DT>
	<DD><B>6. </B>Do not add any menu entries into the Width cascading menu at this time
	(that is left for an exercise at the end of the chapter). Instead, select the menu
	entry below the Width entry and open its properties dialog. Specify the caption as
	&amp;Colors and check the Pop-up check box.
	<P>
	<DT></DT>
	<DD><B>7. </B>In the colors cascading menu, add the color menu entries as you did
	for the IDR_DAY11TYPE menu, using the same property settings. You can select the
	ID from the drop-down list of IDs, if you would rather search for them instead of
	type. When you finish, your menu should look like the one in Figure 11.4.
	<P>
	<DT></DT>
	<DD><B>8. </B>Select the Class View tab in the workspace pane.
	<P>
	<DT></DT>
	<DD><B>9. </B>Select the CDay11View class. Open the Class Wizard by selecting View|ClassWizard
	from the menu.
	<P>
</DL>

<P><A HREF="javascript:popUp('11fig04.gif')"><B>FIGURE 11.4.</B></A><B> </B><I>The
context menu design.</I></P>

<P><I></I>

<DL>
	<DT><I></I></DT>
	<DD><B>10. </B>Add a function for the WM_CONTEXTMENU event message on the CDay11View
	class.
	<P>
	<DT></DT>
	<DD><B>11. </B>Edit the function, adding the code in Listing 11.4.
	<P>
</DL>

<H4>LISTING 11.4. THE CDay11View OnContextMenu FUNCTION.</H4>
<PRE> 1: void CDay11View::OnContextMenu(CWnd* pWnd, CPoint point)
 2: {
 3:     // TODO: Add your message handler code here
 4: 
 5:     ///////////////////////
 6:     // MY CODE STARTS HERE
 7:     ///////////////////////
 8: 
 9:     CMenu menu;
10: 
11:     // Load the context menu
12:     menu.LoadMenu(IDR_CONTEXTMENU);
13:     // Get the first sub menu (the real menu)
14:     CMenu *pContextMenu = menu.GetSubMenu(0);
15: 
16:     // Display the context menu for the user
17:     pContextMenu-&gt;TrackPopupMenu(TPM_LEFTALIGN | 
18:         TPM_LEFTBUTTON | TPM_RIGHTBUTTON,
19:         point.x, point.y, AfxGetMainWnd());
20: 
21:     ///////////////////////
22:     // MY CODE ENDS HERE
23:     ///////////////////////
</PRE>

<PRE>24: }</PRE>
<P>This code should all look familiar to you from what you learned on Day 6. If you
compile and run your application now, you should be able to click your right mouse
button on the child window and change your drawing color from the context menu that
opened, as shown in Figure 11.5.</P>
<P><A HREF="javascript:popUp('11fig05.gif')"><B>FIGURE 11.5.</B></A><B> </B><I>Using
the context menu to change drawing colors.</I></P>

<P><I></I>
<H2><A NAME="Heading7"></A>Summary</H2>
<P>That wasn't too bad; was it? After yesterday, you probably needed the easy day
today, along with all the review of what you did yesterday to help it all sink in.
But you did get to learn some new things today. You learned about MDI applications,
what they are, and how they differ from SDI applications. You learned how you could
take a series of menus and use a single event-handler function for all of them. You
also learned how you can create a menu specifically for use as a pop-up context menu
and how you can integrate it into an MDI application.</P>
<P>
<H2><A NAME="Heading8"></A>Q&amp;A</H2>

<DL>
	<DT></DT>
	<DD><B>Q Because it's basically the same code to create an MDI or SDI application,
	why would I want to create an SDI application? Why wouldn't I want to make all my
	applications MDI applications?</B>
	<P>
	<DT><B></B></DT>
	<DD><B>A</B> It depends on the application and how it's going to be used. You probably
	use both types of applications on a daily basis. If you are writing a memo or working
	on a spreadsheet, you are probably using an MDI application. If you are browsing
	the World Wide Web, your Web browser is most likely an SDI application. A simple
	text editor such as Notepad would probably be more difficult for the user as an MDI
	style application, but as an SDI application, it's just about right (for the task
	it handles). Certain applications make more sense implemented as an SDI application
	than as an MDI application. You need to think through how your application is going
	to be used and determine which model it's more suited for.
	<P>
	<DT></DT>
	<DD><B>Q Some entries on my color menu are changing to the wrong color. How can I
	determine the problem?</B>
	<P>
	<DT><B></B></DT>
	<DD><B>A</B> The problem is that the color menu IDs are probably not in sequential
	order or are out of order. You can check them by right-clicking on the Day11 resources
	in the Resource View tab of the workspace pane. Select Resource Symbols from the
	pop-up menu to display a list of the IDs and the numbers assigned to them in alphabetical
	order. Start with the Black ID and make sure that the numbers increase by 1 without
	skipping any numbers. Be sure to check these IDs in the order that the colors appear
	on the menu (and in the color table in the Day11Doc.cpp file), not in the alphabetical
	order in which they are displayed in this list. If you find some errors, you have
	to close Visual C++ and open the Resource.h file in a text editor to renumber the
	IDs correctly. Once you make the corrections (be sure to delete any duplicates),
	save your corrections, restart Visual C++, and recompile your application. The color
	menu should work correctly.
	<P>
</DL>

<H2><A NAME="Heading9"></A>Workshop</H2>
<P>The Workshop provides quiz questions to help you solidify your understanding of
the material covered and exercises to provide you with experience in using what you've
learned. The answers to the quiz questions and exercises are provided in Appendix
B, &quot;Answers.&quot;</P>
<P>
<H3><A NAME="Heading10"></A>Quiz</H3>

<DL>
	<DT></DT>
	<DD><B>1. </B>What are the five base classes that are used in MDI applications?
	<P>
	<DT></DT>
	<DD><B>2. </B>Why do you have to place the ON_COMMAND_RANGE message map entry outside
	the section maintained by the Class Wizard?
	<P>
	<DT></DT>
	<DD><B>3. </B>What argument does ON_COMMAND_RANGE pass to the event function?
	<P>
	<DT></DT>
	<DD><B>4. </B>What event message should you use to display a pop-up menu?
	<P>
</DL>

<H3><A NAME="Heading11"></A>Exercise</H3>
<P>Add the pull-down and context menus for the width, using the same pen widths as
yesterday.</P>
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