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WindowsCE.[Essential Windows CE Application Programming].Jon Wiley & Son.zip

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Publication Date: 03/01/99
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<!--ISBN=0471327476//-->
<!--TITLE=Essential Windows CE Application Programming//-->
<!--AUTHOR=Robert Burdick//-->
<!--PUBLISHER=John Wiley & Sons, Inc.//-->
<!--IMPRINT=Wiley Computer Publishing//-->
<!--CHAPTER=5//-->
<!--PAGES=116-119//-->
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<TR><TD><FONT SIZE="+1"><B>The Today Button Doesn&#146;t Work, Right?</B></FONT>
<P>Click on the Today button in the sample application. The month calendar control switches to today&#146;s date, but the application caption text doesn&#146;t change. This &#147;bug&#148; was left in the sample application to highlight a subtle undesirable feature of the month calendar control.
</P>
<P>It turns out that programmatic changes to the current selection in a month calendar control do not trigger MCN_SELECT or MCN_SELCHANGE notifications. Therefore, the MCM_SETCURSEL message sent in the <I>OnGotoToday</I> function does not cause the MCN_SELECT or MCN_SELCHANGE notifications to be sent. Hence, the main application caption text does not change when the Today button is pressed.</P>
<P>This is a serious oversight in the design of the month calendar control. The application developer must manually trigger the notification handlers for each of these notifications.</P>
<P>One method for fixing this bug is presented in the next section.</P>
</TABLE>

<P>This function simply determines the date that the control currently uses as today&#146;s date with the MCM_GETTODAY message, and then sets the current month calendar control selection by sending MCM_SETCURSEL. MCM_GETTODAY returns a SYSTEMTIME structure representing today&#146;s date. MCM_SETCURSEL takes a SYSTEMTIME telling the control what day to set the current selection to.
</P>
<P><FONT SIZE="+1"><B><I>Before We Move On, Let&#146;s Fix the Bug</I></B></FONT></P>
<P>In the previous section, we pointed out a small bug with the Today button in the month calendar control sample application. This section describes one way to fix this bug.
</P>
<P>The caption text in the main window of the application is changed by the <I>OnSelect</I> function. Pressing the Today button results in a call to the <I>OnGotoToday</I> function. Fixing the bug is as simple as making <I>OnGotoToday</I> appropriately call <I>OnSelect</I>.</P>
<P><I>OnSelect</I> requires handles to the month calendar control and the parent window. These are global variables available to any function in the application. Additionally, <I>OnSelect</I> needs a pointer to an NMSELCHANGE structure. Actually, it only needs the <I>wMonth</I>, <I>wDay</I>, and <I>wYear</I> components of the <I>stSelStart</I> member of such a structure. <I>OnGotoToday</I> already obtains this information by sending an MCM_GETTODAY message. The bug can thus be fixed by replacing the original <I>OnGotoToday</I> function with the following:</P>
<!-- CODE //-->
<PRE>
  void OnGotoToday(HWND hwndCal)
  {
    SYSTEMTIME stToday;
    NMSELCHANGE nmsel;
    memset(&nmsel, 0, sizeof(nmsel));
    SendMessage(hwndCal, MCM_GETTODAY, 0, (LPARAM)&stToday);
    SendMessage(hwndCal, MCM_SETCURSEL, 0, (LPARAM)&stToday);
    nmsel.stSelStart = stToday;
    OnSelect(hwndMonth, hwndMain, &nmsel);
  }
</PRE>
<!-- END CODE //-->
<P>There are very few changes to the <I>OnGotoToday</I> function here. We declare an NMSELCHANGE structure, <I>nmsel</I>, and initialize its contents to zero. After sending the MCM_SETCURSEL message to the month calendar control, we assign the <I>stSelStart</I> member of <I>nmsel</I> to the DATETIME structure retrieved by the MCM_GETTODAY message.</P>
<P><I>hwndMonth</I> and <I>hwndMain</I> are the global variables containing the window handles of the month calendar control and the main application window, respectively. The <I>OnSelect</I> call therefore has all the information it needs to update the main window caption correctly.</P>
<P><FONT SIZE="+1"><B>Month Calendar Control Messages and Notifications</B></FONT></P>
<P>The complete list of the control messages and notifications associated with the month calendar control are described in Tables 5.2 and 5.3.
</P>
<TABLE WIDTH="100%" BORDER RULES="ROWS"><CAPTION ALIGN=LEFT><B>Table 5.2</B> Month Calendar Control Messages
<TR>
<TH ALIGN="LEFT" WIDTH="25%">MESSAGE
<TH ALIGN="LEFT" WIDTH="75%">MEANING
<TR>
<TD VALIGN="TOP">MCM_GETCOLOR
<TD>Retrieves the color of the specified part of the control.
<TR>
<TD VALIGN="TOP">MCM_GETCURSEL
<TD>Gets the SYSTEMTIME structure corresponding to the currently selected date.
<TR>
<TD VALIGN="TOP">MCM_GETFIRSTDAYOFWEEK
<TD>Returns the first day of the week displayed for each week in the control.
<TR>
<TD VALIGN="TOP">MCM_GETMAXSELCOUNT
<TD>Returns the maximum number of days that can be selected at one time in the control.
<TR>
<TD VALIGN="TOP">MCM_GETMAXTODAYWIDTH
<TD>Returns the maximum width of the Today string displayed at the bottom of month calendar controls.
<TR>
<TD VALIGN="TOP">MCM_GETMINREQRECT
<TD>Returns the minimum width and height required to display one full calendar month.
<TR>
<TD VALIGN="TOP">MCM_GETMONTHDELTA
<TD>Returns the number of months that the control advances or retreats when the user taps the right or left month scroll button.
<TR>
<TD VALIGN="TOP">MCM_GETMONTHRANGE
<TD>Returns SYSTEMTIME structures representing the maximum and minimum dates that can be displayed by the control.
<TR>
<TD VALIGN="TOP">MCM_GETRANGE
<TD>Retrieves the maximum and minimum allowable dates set for the control.
<TR>
<TD VALIGN="TOP">MCM_GETSELRANGE
<TD>Gets the range of dates currently selected in a control with the MCS_MULTISELECT style.
<TR>
<TD VALIGN="TOP">MCM_GETTODAY
<TD>Retrieves the date currently set as today&#146;s date in the control
<TR>
<TD VALIGN="TOP">MCM_HITTEST
<TD>Determines which part of the control contains the specified point.
<TR>
<TD VALIGN="TOP">MCM_SETCOLOR
<TD>Sets the color of the specified part of the control.
<TR>
<TD VALIGN="TOP">MCM_SETCURSEL
<TD>Sets the current date selection in the control. Cannot be used with controls with the MCS_MULTISELECT style.
<TR>
<TD VALIGN="TOP">MCM_SETDAYSTATE
<TD>Sets the day state information for days that are currently visible in the control.
<TR>
<TD VALIGN="TOP">MCM_SETFIRSTDAYOFWEEK
<TD>Sets the day (Monday, Tuesday, etc.) to use as the first day of each week displayed in the control.
<TR>
<TD VALIGN="TOP">MCM_SETMAXSELCOUNT
<TD>Sets the maximum number of days that can be selected in a control.
<TR>
<TD VALIGN="TOP">MCM_SETMONTHDELTA
<TD>Sets the number of months the control advances or retreats when a user taps the right or left month scroll button.
<TR>
<TD VALIGN="TOP">MCM_SETRANGE
<TD>Sets the maximum and minimum dates for a control.
<TR>
<TD VALIGN="TOP">MCM_SETSELRANGE
<TD>Sets the range of currently selected dates for a control. Message only applies to controls with the MCS_MULTISELECT style.
<TR>
<TD VALIGN="TOP">MCM_SETTODAY
<TD>Sets the date that the control specifies as today&#146;s date.
</TABLE>
<P>
</P>
<TABLE WIDTH="100%" BORDER RULES="ROWS"><CAPTION ALIGN=LEFT><B>Table 5.3</B> Month Calendar Control Notifications
<TR>
<TH WIDTH="25%" ALIGN="LEFT">NOTIFICATION
<TH WIDTH="75%" ALIGN="LEFT">MEANING
<TR>
<TD VALIGN="TOP">MCN_GETDAYSTATE
<TD>Sent by a control to request day state information used to determine which dates to display in bold.
<TR>
<TD VALIGN="TOP">MCN_SELCHANGE
<TD>Sent by a control anytime the currently selected date or range of dates changes.
<TR>
<TD VALIGN="TOP">MCN_SELECT
<TD>Sent by a control whenever the user explicitly selects a new current date or range of dates, i.e., the user taps a specific date in the calendar.
</TABLE>
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