Knowledge Base

How To Simulate an Incremental Search from a Text Box

Article ID: 166378

Article Last Modified on 7/13/2004

APPLIES TO

This article was previously published under Q166378

SUMMARY

The combo box control has an Incremental Search property that, when set to true (.T.), searches the Control Source of the combo box with each keystroke. Thus, if a user types the string "ABC," the table is searched after each keystroke, first for the letter "A," then the string "AB," then the string "ABC."

While this is a very useful property, the fact that the search is triggered by action rather than inaction causes UI problems--the user may not want to search for each letter of a string as he or she builds it, but rather search for the whole string after it has been fully entered. The text box does not have an incremental search property, but the action can be simulated, and made to search when the user stops typing, rather than when the user is entering the string for which to search.

The code in this article creates a fully editable text box that implements an incremental search procedure. Using a timer, the incremental search is triggered when the user has not pressed a key for a certain timeout period.

MORE INFORMATION

  1. Create a new form, and add the Customer table from the Testdata database (located in the Samples folder in Visual FoxPro 5.0 and the Microsoft Visual Studio\Common\Samples\Data folder in Visual FoxPro 6.0) to the DataEnvironment. Drag the table onto the form to create a grid. Make sure the grid is named Grid1. Add to the form three custom properties: PREVAL, TICKCOUNT, and HOLDVALUE. Change the default values of PREVAL and HOLDVALUE to blank. Change the default value of TICKCOUNT to 0.
  2. Add to the form a custom method named SearchVal. To that method, add the following code: 

          * Only seek if the value in the text box has changed
      IF !(THIS.PREVAL == ALLTRIM(THIS.TEXT1.VALUE))

        * Set the previous value to the current value
        THIS.PREVAL = ALLTRIM(THIS.TEXT1.VALUE)

        * Seek for the text value
        GO TOP
        SEEK THIS.PREVAL

        IF FOUND()
           * The custom property holdvalue is used to store the
           * string the user has entered.
           THISFORM.HOLDVALUE = THIS.PREVAL

           * This sets focus to the grid so that the located
           * record is displayed in the grid and the
           * RecordMark is turned on for the located record
           THISFORM.GRID1.SETFOCUS

           * Reset focus immediately to the text box
           THIS.TEXT1.SETFOCUS
           THIS.TEXT1.VALUE    = THISFORM.HOLDVALUE
           THIS.TEXT1.SELSTART = LEN(THISFORM.HOLDVALUE)
        ENDIF
      ENDIF

  3. Add a timer to the form, and set the Interval property of the timer to 50. In the Timer event of the Timer control, add the following code: 

          THIS.PARENT.TICKCOUNT = THIS.PARENT.TICKCOUNT + 1

      IF THIS.PARENT.TICKCOUNT >= 20
        THIS.PARENT.TICKCOUNT = 0
        THIS.PARENT.SEARCHVAL()
      ENDIF

  4. Add a text box to the form. Do not specify a control source for the text box. In the Load event of the form, enter the following command: 

          SET ORDER TO CUST_ID && or whatever the name of the index tag
                           && for the cust_id field is.

  5. Add the following code to the text box KeyPress event procedure: 

          * NOTE: The SHIFT-DIRECTIONKEY highlighting works, but is non
      * standard. For example, SHIFT-LEFT-ARROW highlighting three
      * characters to the right, then hitting the right arrow key, only
      * increments the current position by one. In most editors, doing
      * this would increment the current position by four.  In order to
      * emulate this behavior, however, it would be necessary to save
      * the last key pressed in a variable, then check it to find out
      * in which direction we were last moving, then perform a
      * calculation ... it just didn't seem worth the effort.

      LOCAL nPos, nLen, nSel

      nPos = THIS.SELSTART         && current pos of the cursor
      nLen = LEN(ALLTRIM(THIS.VALUE))   && length of text in textbox
      nSel = THIS.SELLENGTH         && number of selected chars

      THIS.PARENT.TICKCOUNT = 0

      * Turn off all default processing of the Keypress Event;
      * this is necessary for code to work
      NODEFAULT

      DO CASE
         * Tests/traps for nKeycode >= 65, <= 122 (limits input to
         * alpha characters), nKeycode = 32 (allows for spaces). To
         * allow for input of numerals and/or other characters,
         * refer to the INKEY() topic in the Help file for codes
         * 39 is for single quote
         CASE (nKeyCode >= 65 AND nKeyCode <= 122) OR nKeyCode = 32;
            OR nKeyCode  = 44 OR  nKeyCode  = 45   OR nKeyCode = 39

            * Insert the new character in the right place
            THIS.VALUE = UPPER(LEFT(THIS.VALUE, nPos) +   ;
              CHR(nKeyCode) + RIGHT(THIS.VALUE,;
              nLen - (nPos + nSel)))

            * Increment our position holder so we are placed
            * after the new letter
            nPos = nPos + 1
            nSel = 0

         * Tests/traps for the SHIFT-LEFT-ARROW combo (highlight-left)
         CASE nKeyCode = 52
            * Move one to the left, increase number selected by one
            IF  nPos > 0
               nPos = nPos - 1
               nSel = nSel + 1
            ENDIF

         * Tests/traps for the SHIFT-RIGHT-ARROW combo (highlight-right)
         CASE nKeyCode = 54
            * Increase number selected by one, if there is more to
            * select
            IF (nPos + nSel) < nLen
               nSel = nSel + 1
            ENDIF

         * Tests/traps for the SHIFT-HOME combo (highlight-left-end)
         CASE nKeyCode = 55
            * Set the number of characters selected to the number of
            * characters between our current position and the start
            * position, then move to the start position
            nSel = nSel + nPos
            nPos = 0

         * Tests/traps for the SHIFT-END combo (higlight-right-end)
         CASE nKeyCode = 49
            * Set the number of characters selected to the number to
            * the right of our current position
            nSel = nLen - nPos

         * Tests/traps for the LEFT-ARROW key
         CASE nKeyCode = 19
            * Deselect any selected characters
            nSel = 0

            * Move left one
            IF nPos > 0
               nPos = nPos - 1
            ENDIF

         * Tests/traps for the RIGHT-ARROW key
         CASE nKeyCode = 4
            * Deselect any selected characters
            nSel = 0

            * Move right one
            IF  nPos < nLen
               nPos = nPos + 1
            ENDIF

         * Tests/traps for the HOME key
         CASE nKeyCode = 1
            * Deselect any selected characters
            nSel = 0

            * Move to the start
            nPos = 0

         * Tests/traps for the END key
         CASE nKeyCode = 6
            * Deselect any selected characters
            nSel = 0

            * Move to the end
            nPos = nLen

         * Tests/traps for the DELETE key
         CASE nKeyCode = 7
            * If we have not 'highlighted' the letter we want to delete,
            * the count of letters to delete will be zero, so we have
            * to manually set the letter to remove
            IF  nSel = 0
               nSel = 1
            ENDIF

            * Rebuild the string without the deleted character(s)
            THIS.VALUE = LEFT(THIS.VALUE, nPos) + ;
                RIGHT(THIS.VALUE, nLen - (nPos + nSel))

            * Deselect any selected characters
            nSel = 0

         * Tests/traps for the BACKSPACE key
         CASE nKeycode = 127
            * If no letters are 'highlighted', just delete the one
            * before the cursor and
            * move the cursor back one
            IF nSel = 0
               IF  nPos > 0
                  THIS.VALUE = LEFT(THIS.VALUE, nPos - 1) + ;
                    RIGHT(THIS.VALUE, nLen - nPos)
                    nPos = nPos - 1
               ENDIF

               * If letters are highlighted, remove the block of
               * highlighted letters, and don't move the cursor
               * (just like hitting DELETE)
            ELSE
               THIS.VALUE = LEFT(THIS.VALUE, nPos) + ;
                  RIGHT(THIS.VALUE, nLen - (nPos + nSel))
            ENDIF

            * Deselect any selected characters
            nSel = 0

      ENDCASE

      * Get rid of whitespace at the end of the entered word
      IF nLen != LEN(ALLTRIM(THIS.VALUE))
         THIS.MAXLENGTH = LEN(ALLTRIM(THIS.VALUE)) + 1
      ENDIF

      * This moves the cursor to the current position in the string in the
      * text box
      THIS.SELSTART  = nPos

      * And this selects the proper number of characters
      THIS.SELLENGTH = nSel

  6. Save and run the form. Type a search field into the text box. After a brief pause, any matching fields should be located within the database and pointed to on the Grid. Experiment with different timeout periods until you find one with which you are comfortable.

General Notes

  • In this example it is assumed that the text box is named Text1. If the name of that text box is different, modify the code accordingly.
  • The NODEFAULT command turns off all of the default processing of the KeyPress event and allows the code to completely control the processing of the key presses. This command is necessary.
  • As is noted in a few of the comments, the edit emulation is not perfect, but it is fairly close to target.
(c) Microsoft Corporation 1997, All Rights Reserved. Contributions by Robert Mobbs, Microsoft Corporation.

Keywords: kbhowto kboop kbdesigner KB166378


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