Q266265: HOWTO: Implement MatchedWithList Validation Check in ComboBox

Article: Q266265
Product(s): Microsoft Visual Basic for Windows
Version(s): 5.0,6.0
Operating System(s): 
Keyword(s): kbVBp kbGrpDSVBDB kbDSupport
Last Modified: 31-MAR-2001

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The information in this article applies to:

- Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 
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SUMMARY
=======

A simple ComboBox control whose Style property has been set to 0-Dropdown Combo
permits a user to manually make an entry into its text edit portion without
selecting a value displayed in its drop-down list. The simple ComboBox control
does not expose a Boolean property (identical to the MatchedWithList property of
the OLEDB DataCombo control) that can be used to determine if the value that is
keyed into the edit portion matches one of the elements in the list. This is an
important validation check that can be very useful when using a simple drop-down
ComboBox.

A generic, reusable routine can be written by using Visual Basic code to
implement this validation check for a simple drop-down ComboBox control. This
article documents the reusable code that can be used to address this
requirement.

MORE INFORMATION
================

Code to Implement the MatchedWithList Validation Check 
------------------------------------------------------

Copy-and-paste the following code into the Change event procedure of a simple
drop-down ComboBox (whose Style has been set to 0-Dropdown Combo for which you
wish to implement the MatchedWithList validation check. You can modify the
message to be displayed to the user when the check fails. The validation check
fails when a character that is keyed into the edit portion results in a string
that does not match an initial substring of any of the elements in the list
portion. The initial substring that is extracted from each of the list elements
comprises of the first "N" characters, "N" being the length of the string in the
edit portion of the ComboBox.

  Dim listcount As Integer
  Dim textlen As Integer
  Dim matchexists As Boolean

  textlen = Len(Combo1.Text)
  For listcount = 0 To Combo1.listcount - 1
   If UCase(Mid(Combo1.List(listcount), 1, textlen)) = UCase(Combo1.Text) Then
     matchexists = True
     Exit For
   End If
  Next

  If Not matchexists Then
   MsgBox "Value not present in the list... Kindly enter a valid value.."
  End If

Steps to Test the Routine
-------------------------

1. Create a new standard EXE project in Visual Basic. Form1 is created by
  default.

2. Add a ComboBox control to Form1 from the toolbox.

3. Cut-and-paste the following code into the Form module:

  Private Sub Combo1_Change()

  Dim listcount As Integer
  Dim textlen As Integer
  Dim matchexists As Boolean

  textlen = Len(Combo1.Text)
  For listcount = 0 To Combo1.listcount - 1
   If UCase(Mid(Combo1.List(listcount), 1, textlen)) = UCase(Combo1.Text) Then
     matchexists = True
     Exit For
   End If
  Next

  If Not matchexists Then
   MsgBox "Value not present in the list... Kindly enter a valid value.."
  End If

  End Sub

  Private Sub Form_Load()
  Combo1.AddItem "Sam"
  Combo1.AddItem "Paul"
  Combo1.AddItem "Peter"
  Combo1.Text = ""
  End Sub

4. Run the project, and then type in appropriate values in the edit portion of
  the ComboBox to test the routine.

  For example, try typing the following to evaluate the outcome of the
  validation:

  "Same, Pater, Paul, Paul" (without the quotation marks)

  Note that in the first three cases, the validation message pops up as soon as
  the first character (e,a, and d) that results in a NoMatch is keyed into the
  edit portion.

Additional query words:

======================================================================
Keywords          : kbVBp kbGrpDSVBDB kbDSupport 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500 kbVBA600 kbVB500 kbVB600
Version           : :5.0,6.0
Issue type        : kbhowto

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