How to Create a "Windows-type" Incremental Search Box in VFP

• Microsoft Visual FoxPro for Windows versions 3.0, 3.0b

SUMMARY

Although the default List Box control has basic incremental search capabilities, the list box must have focus for the function to work. Its functionality differs from the implementation found in other Windows applications, such as the Search option of Help, where the string to be searched for is entered into a text box above a list box that displays the first matching item as each character is entered.

This article describes how to create a technique that allows a list box to searched incrementally, regardless of its RowSource type.

MORE INFORMATION

1. Create a new form in Form Designer.

2. In the Data Environment, add Samples\Data\Customer.DBF.

3. In the form, add a text box, and below it, add a list box.

4. Set the list box RowSource Type as 6-Fields, RowSource as Company.

5. In the InteractiveChange event of the text box, enter the following:

      LOCAL nIndex, oList      && prevent conflict with other variables
      oList = thisform.List1   && create object reference to list box
   
      FOR nIndex = 1 TO oList.ListCount   && loop through each item
   
         * compare the item in the list with the string entered
         IF UPPER( oList.ListItem(nIndex) ) = UPPER( ALLTRIM( this.Value ) )
            oList.ListIndex = nIndex   && select this item if matched
            EXIT               && drop out of loop
         ENDIF
   
      ENDFOR
   
      oList.Refresh       && update the display to show selected item
   
   

NOTE: Performance is effected by the number of records and the position of the item to be found within the list. Performance is improved by dividing the list into portions and substituting variables in the FOR statement which lowers the number of items to compare the text string with. In this example, the list is divided into quarters:

   LOCAL cVal, cLen, c1st, c2nd, c3rd, n1st, n2nd, n3rd, nTop, nEnd, ;
         nMax, oList
   oList = Thisform.List1
   * 1st = 1 to n2nd-1
   nMax = oList.ListCount
   n1st = INT( nMax * .25 ) && 1st quarter
   n2nd = INT( nMax * .50 ) && 2nd quarter
   n3rd = INT( nMax * .75 ) && 3rd quarter
   c1st = UPPER( oList.ListItem[ n1st ] )   && avoids case sensitivity
   c2nd = UPPER( oList.ListItem[ n2nd ] )   &&   when list contains
   c3rd = UPPER( oList.ListItem[ n3rd ] )   &&   mixed case entries
   cVal = ALLTRIM( UPPER( this.Value ) )    && first character caps
   cLen = LEN( cVal )

   DO CASE
     CASE cVal <= LEFT( c1st, cLen )
       nTop = 1
       nEnd = n1st
     CASE cVal <= LEFT( c2nd, cLen )
       nTop = n1st + 1
       nEnd = n2nd
     CASE cVal <= LEFT( c3rd, cLen )
       nTop = n2nd + 1
       nEnd = n3rd
     OTHERWISE
       nTop = n3rd + 1
       nEnd = nMax
   ENDCASE

   FOR nIndex = nTop TO nEnd   && loop through each item within range
      IF UPPER( oList.ListItem[ nIndex ] ) = cVal
         oList.ListIndex = nIndex   && select this item if matched
         EXIT                  && drop out of loop
      ENDIF
   ENDFOR

   oList.Refresh               && update the display to show selected item

   Create the following two new Form properties: cLimit[9] and nLimit[9]

   In the Init event of the form, enter:

      LOCAL nDx, nMax
      oLst = this.List1  && object reference to this form''''''''s list box
      nMax = oLst.ListCount     && divide into tenths

   FOR nDx = 1 TO 9

      * assign number at each tenth boundary (used as index into list)
      this.nLimit[ nDx ] = INT( nMax * ( .10 * nDx ) )

      * assign list item found at this position in the list
      this.cLimit[ nDx ] = UPPER( oLst.ListItem[ this.nLimit[ nDx ] ] )

   ENDFOR

   LOCAL cVal, cLen, nTop, nEnd, nIdx, nDex, oLst
   oLst = thisform.list1
   cVal = ALLTRIM( UPPER( this.Value ) )
   cLen = LEN( cVal )

   * if not found in the sections checked, default to the last section
   nTop = thisform.nLimit[ 9 ] + 1  && i.e., one past the end of the 9th
   nEnd = oLst.ListCount            &&    section to the end of the list

   IF cVal <= LEFT( thisform.cLimit[ 1 ], cLen ) && compare to 1st element
      nTop = 1
      nEnd = thisform.nLimit[1]
   ELSE
      FOR nIdx = 2 TO 9  && loop through the remaining section limits
         IF cVal <= LEFT( thisform.cLimit[ nIdx ], cLen )
            nTop = thisform.nLimit[ nIdx - 1 ] + 1 && previous end plus 1
            nEnd = thisform.nLimit[ nIdx ]  && limit of current section
            EXIT      && drop out of loop since section is found
         ENDIF
      ENDFOR
   ENDIF

   * the remaining code is the same structure as in the previous example
   FOR nDex = nTop TO nEnd   && loop through each item with range

      IF UPPER( oLst.ListItem[ nDex ] ) = cVal
         oLst.ListIndex = nDex
         EXIT
      ENDIF
   ENDFOR

   oLst.Refresh