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

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<B>Essential Windows CE Application Programming</B>
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<I>(Publisher: John Wiley & Sons, Inc.)</I>
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Author(s): Robert Burdick
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ISBN: 0471327476
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Publication Date: 03/01/99
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<P><FONT SIZE="+1"><B>Managing Records More Cleanly</B></FONT></P>
<P>The preceding examples of how to write and read database records leave something to be desired. In both cases, you might have been left with the impression that Windows CE database applications only work with record data in raw binary form. While it is true that the <I>CeReadRecordProps</I> always return an LPBYTE array of data, and <I>CeWriteRecordProps</I> always writes record information as a collection of somewhat cumbersome CEPROPVAL structures, it is possible to write your applications in such a way that the rest of your application can treat database records in a more natural form. Specifically, your application can define a structure that is used to represent the more abstract notion of records in your database.</P>
<P>For example, in the case of the phone list application, it seems natural to represent an entry in the phone list with a structure like this:</P>
<!-- CODE SNIP //-->
<PRE>
   typedef struct _PhoneRecord
   &#123;
     TCHAR lpszLastName[MAX_NAME_LENGTH];
     TCHAR lpszFirstName[MAX_NAME_LENGTH];
     TCHAR lpszPhoneNumber[MAX_NAME_LENGTH];*
     int nDept;
   &#125;PHONERECORD, *LPPHONERECORD;
</PRE>
<!-- END CODE SNIP //-->
<P>No CEPROPVALSs, CEOIDs, or other abstract database concepts here. A phone record is just a collection of values of C data types that we know and love. When users enter new records through the application&#146;s user interface, the application code can assign the values entered into the appropriate fields of an instance of this clear-cut data type. The mechanics of turning the elements of this structure into the form required in order to write the record to the database can be left to the inner workings of one simple <I>ReadRecord</I> function:</P>
<!-- CODE //-->
<PRE>
   EOID ReadRecord(LPPHONERECORD lppr)
   &#123;
    WORD cProps = 0;
    LPBYTE pBuf=NULL;*
    DWORD cbByte = 0;*
    PCEPROPVAL pVals;*
    CEOID oid;
    int i;
    oid = CeReadRecordProps(hDBase, CEDB_ALLOWREALLOC,
     &#38;cProps, NULL,&#38;pBuf, &#38;cbByte);
    pVals = (PCEPROPVAL)pBuf;
    for (i=0; i&lt;cProps; i&#43;&#43;)
    &#123;
     switch(HIWORD(pVals[i].propid))
     &#123;
      case PL_LASTNAME_INDEX:
       lstrcpy(lppr-&gt;lpszLastName,
        pVals[i].val.lpwstr);
       break;
      case PL_FIRSTNAME_INDEX:
       lstrcpy(lppr-&gt;lpszFirstName,
        pVals[i].val.lpwstr);
       break;
      case PL_PHONENUMBER_INDEX:
       lstrcpy(lppr-&gt;lpszPhoneNumber,
        pVals[i].val.lpwstr);
       break;
      case PL_DEPT_INDEX:
       lppr-&gt;nDept = pVals[i].val.iVal;
       break;
      default:
       break;
     &#125;       //End of switch statement
    &#125;        //End of for (i=0; i&lt;cProps; i&#43;&#43;) loop
    LocalFree(pBuf);
    return (oid);
   &#125;
</PRE>
<!-- END CODE //-->
<P>Writing phone list records can be abstracted in much the same way with <I>WriteRecord</I>:</P>
<!-- CODE //-->
<PRE>
   CEOID WriteRecord(LPPHONERECORD lppr)
   &#123;
     CEPROPVAL cePropVal[PROPERTY_COUNT];
     CEOID ceoid;
     HANDLE hDBase;
     WORD wCurrent = 0;
     hDBase = OpenPhoneDatabase(szDBaseName, 0,
      CEDB_AUTOINCREMENT, NULL, &#38;ceoidDBase);
     memset(&#38;cePropVal, 0, sizeof(CEPROPVAL)*PROPERTY_COUNT);
     cePropVal[wCurrent].propid = PL_LASTNAME;
     cePropVal[wCurrent&#43;&#43;].val.lpwstr = lppr-&gt;lpszLastName;
     cePropVal[wCurrent].propid = PL_FIRSTNAME;
     cePropVal[wCurrent&#43;&#43;].val.lpwstr = lppr-&gt;lpszFirstName;
     cePropVal[wCurrent].propid = PL_PHONENUMBER;
     cePropVal[wCurrent&#43;&#43;].val.lpwstr = lppr-&gt;lpszPhoneNumber;
     cePropVal[wCurrent].propid = PL_DEPT;
     cePropVal[wCurrent&#43;&#43;].val.iVal = lppr-&gt;nDept;
     ceoid = CeWriteRecordProps(hDBase, 0, wCurrent,
      cePropVal);
     CloseHandle(hDBase);   /Close the database
     return (ceoid);
   &#125;
</PRE>
<!-- END CODE //-->
<P>The rest of the application can now treat phone list data in the way that you would normally model the concept of a record, as a standard C structure.
</P>
<H3><A NAME="Heading9"></A><FONT COLOR="#000077">Searching for Records</FONT></H3>
<P>The function used for searching for records is <I>CeSeekDatabase</I>:</P>
<!-- CODE SNIP //-->
<PRE>
   CeSeekDatabase(hDatabase, dwSeekType, dwValue, lpdwIndex);
</PRE>
<!-- END CODE SNIP //-->
<P><I>hDatabase</I> is a handle to the open database. <I>dwSeekType</I> is a DWORD that indicates to the function what kind of database search to perform. It also defines where the database current record pointer is positioned at the end of the seek operation. <I>lpdwIndex</I>, the last parameter, is a pointer to a DWORD that <I>CeSeekDatabase</I> uses to return the 0-based index of the record that was found by the seek operation. <I>dwValue</I> has different meanings depending on the value of <I>dwSeekType</I>.</P><P><BR></P>
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