ch14.htm

Visual C++ 的学习资料 Visual C++ 的学习资料

	</TR>
	<TR ALIGN="LEFT" rowspan="1">
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>IDI_HAND</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP">Stop sign icon</TD>
	</TR>
	<TR ALIGN="LEFT" rowspan="1">
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>IDI_QUESTION</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP">Question mark icon</TD>
	</TR>
	<TR ALIGN="LEFT" rowspan="1">
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>IDI_EXCLAMATION</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP">Exclamation point icon</TD>
	</TR>
	<TR ALIGN="LEFT" rowspan="1">
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>IDI_ASTERISK</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP">Asterisk or information icon</TD>
	</TR>
	<TR ALIGN="LEFT" rowspan="1">
		<TD ALIGN="LEFT" VALIGN="TOP"><TT>IDI_WINLOGO</TT></TD>
		<TD ALIGN="LEFT" VALIGN="TOP">Windows logo icon</TD>
	</TR>
</TABLE>
</P>
<P>Using these cursors is similar to using stock objects. Listing 14.6 uses the <TT>IDC_UPARROW</TT>
cursor in response to <TT>WM_SETCURSOR</TT>.
<H4><FONT COLOR="#000077">TYPE: Listing 14.6. Using a standard Windows cursor.</FONT></H4>
<PRE><FONT COLOR="#0066FF"><TT>BOOL CAboutDlg::OnSetCursor(CWnd* pWnd, UINT nHitTest,</TT>
<TT>                            UINT message)</TT>
<TT>{</TT>
<TT>    // Load and set the new cursor. Return TRUE to stop</TT>
<TT>    // further processing of this message.</TT>
<TT>    CWinApp* pApp = AfxGetApp();</TT>
<TT>    HICON hIcon = pApp-&gt;LoadStandardCursor( IDC_UPARROW );</TT>
<TT>    SetCursor( hIcon );</TT>
<TT>    return TRUE;</TT>
<TT>}</TT>
</FONT></PRE>
<P>A cursor set in response to the <TT>WM_SETCURSOR</TT> message will interfere with
the remaining examples in the hour. After you are finished with this example, remove
the <TT>OnSetCursor</TT> function using ClassWizard.
<H3><FONT COLOR="#000077"><B>Changing the Cursor to the Hourglass</B></FONT></H3>


<BLOCKQUOTE>
	<P>
<HR>
<B> </B><FONT COLOR="#000077"><B>Just a Minute:</B></FONT><B> </B>When a large amount
	of processing is performed, ignoring input from the user is common. It's considered
	good manners for a Windows program to change the cursor to an hourglass when user
	input won't be acknowledged. 
<HR>


</BLOCKQUOTE>

<P>A common place to ignore user input is during long initialization routines. It's
common to display a user interface but disregard user input until the initialization
is complete. It can take several seconds before an application is ready for input,
particularly in applications that work with large amounts of data that must be initialized.
In these cases, you should use the <TT>BeginWaitCursor</TT> and <TT>EndWaitCursor</TT>
functions.</P>
<P>To demonstrate how these functions are used, add a message-handling function to
the <TT>CAboutDlg</TT> class using ClassWizard. Add a message-handling function for
<TT>WM_TIMER</TT>, and accept the default function name provided by ClassWizard.
Listing 14.7 contains the source code for the <TT>OnInitDialog</TT> and <TT>OnTimer</TT>
functions.
<H4><FONT COLOR="#000077">TYPE: Listing 14.7. Modifying OnInitDialog and OnTimer
to use the hourglass cursor.</FONT></H4>
<PRE><FONT COLOR="#0066FF"><TT>BOOL CAboutDlg::OnInitDialog()</TT>
<TT>{</TT>
<TT>    CDialog::OnInitDialog();</TT>
<TT>    CWinApp* pApp = AfxGetApp();</TT>
<TT>    if( pApp != 0 )</TT>
<TT>    {</TT>
<TT>        m_hIconOkay = pApp-&gt;LoadIcon( IDI_GREEN );</TT>
<TT>        m_hIconCancel = pApp-&gt;LoadIcon( IDI_RED );</TT>
<TT>        ASSERT(m_hIconOkay);</TT>
<TT>        ASSERT(m_hIconCancel);</TT>
<TT>        m_btnOkay.SetIcon( m_hIconOkay );</TT>
<TT>        m_btnCancel.SetIcon( m_hIconCancel );</TT>
<TT>    }</TT>
<TT>    SetCapture();</TT>
<TT>    BeginWaitCursor();</TT>
<TT>    SetTimer( 1, 15000, NULL );</TT>
<TT>    return TRUE;</TT>
<TT>}</TT>

<TT>void CAboutDlg::OnTimer(UINT nIDEvent)</TT>
<TT>{</TT>
<TT>    ReleaseCapture();</TT>
<TT>    EndWaitCursor();</TT>
<TT>    KillTimer( 1 );</TT>
<TT>}</TT>
</FONT></PRE>
<P>In Listing 14.7, the <TT>OnInitDialog</TT> function simulates the beginning of
a long processing period. The <TT>SetCapture</TT> and <TT>BeginWaitCursor</TT> functions
are called to change the cursor to an hourglass. While changed, the cursor cannot
be used to interact with any controls. A five-second timer is started, which calls
the <TT>OnTimer</TT> function when the timer expires. The <TT>OnTimer</TT> function
restores the cursor and kills the timer.


<BLOCKQUOTE>
	<P>
<HR>
<B> </B><FONT COLOR="#000077"><B>Time Saver:</B></FONT><B> </B>The order of the statements
	in <TT>OnInitDialog</TT> is important. Before calling <TT>BeginWaitCursor</TT>, the
	mouse must be captured using <TT>SetCapture</TT>; otherwise, the hourglass cursor
	immediately reverts to the arrow cursor. 
<HR>


</BLOCKQUOTE>

<H3><FONT COLOR="#000077"><B>Clipping a Cursor</B></FONT></H3>
<P>There are times when restricting a cursor to a single window is convenient. This
is usually the case when you are working with error messages, or in other situations
in which you would like to force the user to make a selection. Forcing a cursor to
stay with the boundaries of a single window is known as <I>clipping the cursor</I>.</P>
<P>As an example, force the cursor to stay over the Cursor project's About dialog
box. Using ClassWizard, add message-handling functions for <TT>WM_DESTROY</TT> and
<TT>WM_MOVE</TT> to the <TT>CAboutDlg</TT> class. Add the source code in Listing
14.8 to the <TT>CAbout::OnMove</TT> and <TT>CAbout::OnDestroy</TT> member functions.
<H4><FONT COLOR="#000077">TYPE: Listing 14.8. Source code used to form a clipping
region for the cursor.</FONT></H4>
<PRE><FONT COLOR="#0066FF"><TT>void CAboutDlg::OnMove(int x, int y)</TT>
<TT>{</TT>
<TT>    CDialog::OnMove(x, y);</TT>

<TT>    CRect   rcCursor;</TT>
<TT>    GetWindowRect( rcCursor );</TT>
<TT>    ClipCursor( &amp;rcCursor );</TT>
<TT>}</TT>

<TT>void CAboutDlg::OnDestroy()</TT>
<TT>{</TT>
<TT>    ClipCursor( NULL );</TT>
<TT>    CDialog::OnDestroy();</TT>
<TT>}</TT>
</FONT></PRE>
<P>When the MFC framework creates the About dialog box and moves it to the center
of the view window, the <TT>WM_MOVE</TT> message is sent to the <TT>CAboutDlg</TT>
class. Inside the <TT>OnMove</TT> function, the dialog box's screen coordinates are
used to set the clipping rectangle for the cursor. When the dialog box is destroyed,
the <TT>WM_DESTROY</TT> message is handled by the <TT>CAboutDlg::OnDestroy</TT> function,
and the clipping rectangle is reset.


<BLOCKQUOTE>
	<P>
<HR>
<B> </B><FONT COLOR="#000077"><B>CAUTION:</B></FONT><B> </B>It is important to reset
	the cursor clipping region by calling <TT>ClipCursor(NULL)</TT> when the window is
	destroyed or when the clipping region is no longer needed. If this function isn't
	called, the cursor will be restricted to the requested rectangle even after the window
	has disappeared. 
<HR>


</BLOCKQUOTE>

<H2><FONT COLOR="#000077"><B>Summary</B></FONT></H2>
<P>In this hour you learned how to use icons in Windows programs. You learned how
to change the main program icon, as well as child icons. You used a sample program
to learn the functions used to load, draw, and destroy icon resources. You also learned
how to use cursors to provide feedback when programming Windows applications.
<H2><FONT COLOR="#000077"><B>Q&amp;A</B></FONT></H2>

<DL>
	<DD><B>Q What are the advantages of providing an icon for a button versus using the
	MFC <TT>CBitmapButton</TT> class?</B><BR>
	<BR>
	<B>A</B> Assigning an icon to a button is much simpler than using the <TT>CBitmapButton</TT>
	class. It is also more efficient because Windows will handle drawing the image instead
	of the MFC class library.<BR>
	<BR>
	<B>Q The <TT>CDC::DrawIcon</TT> function will only draw an icon the size of its original
	image. How can I draw an icon larger than its original size?</B><BR>
	<BR>
	<B>A</B> You can use the <TT>DrawIconEx</TT> function to draw an icon to an arbitrary
	size. Unlike <TT>DrawIcon</TT>, the <TT>DrawIconEx</TT> function isn't a member of
	the <TT>CDC</TT> class. You must pass the internal handle used by the <TT>CDC</TT>
	object as the first parameter in the call to <TT>DrawIconEx</TT>, as shown in the
	<TT>OnDraw</TT> function:
</DL>



<BLOCKQUOTE>
	<PRE><FONT COLOR="#0066FF"><TT>void CMyTestView::OnDraw(CDC* pDC)</TT>
<TT>{</TT>
<TT>    CRect rc;</TT>
<TT>    GetClientRect(&amp;rc);</TT>
<TT>    HICON hIcon = AfxGetApp()-&gt;LoadIcon(IDI_TEST);</TT>
<TT>    DrawIconEx(pDC-&gt;m_hDC,</TT>
<TT>               0,</TT>
<TT>               0,</TT>
<TT>               hIcon,</TT>
<TT>               rc.Width(),</TT>
<TT>               rc.Height(),</TT>
<TT>               0,</TT>
<TT>               NULL,</TT>
<TT>               DI_NORMAL);</TT>
<TT>    DestroyIcon(hIcon);</TT>
<TT>}</TT></FONT></PRE>

</BLOCKQUOTE>

<PRE><FONT COLOR="#0066FF"><TT></TT></FONT></PRE>

<DL>
	<DD>The really interesting parameters passed to <TT>DrawIconEx</TT> are parameters
	five and six; these are the width and height of the final image.
</DL>

<H2><FONT COLOR="#000077"><B>Workshop</B></FONT></H2>
<P>The Workshop is designed to help you anticipate possible questions, review what
you've learned, and begin thinking ahead to putting your knowledge into practice.
The answers to the quiz are in Appendix B, &quot;Quiz Answers.&quot;
<H3><FONT COLOR="#000077"><B>Quiz</B></FONT></H3>

<DL>
	<DD>1. What function is used to associate an icon with a pushbutton?<BR>
	<BR>
	2. What is the name of the area on the cursor that is used as the current mouse location?<BR>
	<BR>
	3. What function is used to restrict a cursor to a specific rectangle?<BR>
	<BR>
	4. What function is used to trap all mouse messages?<BR>
	<BR>
	5. What function is used to change the current cursor?<BR>
	<BR>
	6. What message must be handled in order to change the current cursor?<BR>
	<BR>
	7. What is the size of an application's small icon?<BR>
	<BR>
	8. What function is used to change to the hourglass cursor?
</DL>

<H3><FONT COLOR="#000077"><B>Exercise</B></FONT></H3>

<DL>
	<DD>1. Modify Listing 14.5 so that the hourglass cursor is shown unless the mouse
	is over the OK or Cancel button.<FONT COLOR="#000077"></FONT>
</DL>

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