How to Fill a List Box with Snapshot When Contents are Unknown

- Professional and Enterprise Editions of Microsoft Visual Basic,

  16-bit and 32-bit, for Windows version 4.0

SUMMARY

This article demonstrates how to fill a list box with a snapshot when the contents of the snapshot are unknown at design time. The example uses TAB characters to create a columnar display, and it adds a horizontal scroll bar so the user can view the entire record.

MORE INFORMATION

When handling result sets from database queries that produce variable result sets, you may find it useful to have a generic function display the contents in a list box.

The following example defines a Sub (Fill_List) that accepts a list-box control and snapshot as parameters and fills the list box with the contents of the snapshot. The function can be easily modified to accept a table or dynaset object as well.

For additional information, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID :Q71067
   TITLE      :How to Set Tab Stops in a List Box in Visual Basic

Step-by-Step Instructions for Creating the Program

1. Start a new project in Visual Basic. Form1 is created by default.

2. Add a command button (Command1) and a list box (List1) to the form. Set the caption property of Command1 to "Fill list."

3. Add the following code to the form's general declarations section: (For the code below to work correctly, the user must have a reference to either the "Microsoft DAO 3.0 Object Library" or to the "Microsoft DAO 2.5/3.0 Compatibility Library)."

   Option Explicit Const WM_USER = &H400 #If Win16 Then

        Const LB_SETTABSTOPS = WM_USER + 19
        Const LB_SETHORIZONTALEXTENT As Long = WM_USER + 21
        Private Declare Function SendMessage Lib "User" (ByVal hwnd As _
          Integer,ByVal wMsg As Integer, ByVal wParam As Integer, _
          lParam As Any) As Long
   

        Dim scrollbarwidth  As Integer ' Width of horizontal scrollbar.
        Dim numtabs As Integer         ' Number of tabs needed.
        Dim tabstops() As Integer      ' Array of value of tab stop of columnn
   
      #Else
        Const LB_SETTABSTOPS = &H192         ' Has changed in Win32.
        Const LB_SETHORIZONTALEXTENT As Long = &H194   ' Has changed in Win32.
        Private Declare Function SendMessage Lib "user32" Alias _
          "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, _
          ByVal wParam As Long, lParam As Long) As Long
        Dim scrollbarwidth  As Long    ' Width of horizontal scrollbar.
        Dim numtabs As Long            ' Number of tabs needed.
        Dim tabstops() As Long         ' Array of value of tab stop of columnn
   
      #End If
   
      Private Sub Fill_List(lb As ListBox, sn As Recordset)
        Const NUMCHARS = 2  ' Amount of white space between columns.
   
        ' Temporary variables to preserve form font settings:
        Dim hold_fontname As String, hold_fontsize As Integer
        Dim hold_fontbold As Integer, hold_fontitalic As Integer
        Dim hold_fontstrikethru As Integer, hold_fontunderline  As Integer
   
        Dim whiteSpace As Integer, accumtabstops As Integer, _
          dialogUnits As Integer
        Dim fieldVal As String, listline As String
        Dim avgWidth As Single
   
        Dim i As Integer                ' Used in For Next loops.
        Dim biggest_value() As Single   ' Array of longest string of columns.
        Dim retval As Long              ' Return value of SendMessage function
   
   
        ' Save form's font settings so we can use the form to calculate the
        ' TextWidth / Height of the strings to go into the list box.
        hold_fontname = Me.FontName
        hold_fontsize = Me.FontSize
        hold_fontbold = Me.FontBold
        hold_fontitalic = Me.FontItalic
        hold_fontstrikethru = Me.FontStrikethru
        hold_fontunderline = Me.FontUnderline
   
        ' Set form font settings to be identical to list box.
        Me.FontName = lb.FontName
        Me.FontSize = lb.FontSize
        Me.FontBold = lb.FontBold
        Me.FontItalic = lb.FontItalic
        Me.FontStrikethru = lb.FontStrikethru
        Me.FontUnderline = lb.FontUnderline
   
        ' Get the average character width of the current list box font
        ' (in pixels) using the form's TextWidth width method.
        avgWidth = Me.TextWidth _
          ("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
        avgWidth = avgWidth / Screen.TwipsPerPixelX / 52
   
        ' Set the white space you want between columns.
        whiteSpace = avgWidth * NUMCHARS
   
        ReDim biggest_value(0 To sn.Fields.Count - 1)
        ReDim tabstops(1 To sn.Fields.Count)
   
        lb.Clear
   
        ' Loop through the field values for each record in the snapshot.
        ' Calculate the width required for that field value to fit in the list
        ' box. Also, build each line of the list box and add it to the list as
        ' you go.
        While Not sn.EOF
          For i = 0 To sn.Fields.Count - 1
            fieldVal = sn(i) & ""       ' Append "" in case of a null field.
   
            ' The LB_SETTABSTOP message requires coordinates in dialog units
            ' (roughly 4 *, the average character width in pixels).
            dialogUnits = ((Me.TextWidth(fieldVal) / Screen.TwipsPerPixelX + _
              whiteSpace) \ avgWidth) * 4
            If dialogUnits > biggest_value(i) Then
              biggest_value(i) = dialogUnits
            End If
   
            listline = listline & sn(i) & vbTab
          Next i
   
          lb.AddItem listline
          listline = ""
          sn.MoveNext
        Wend
   
        ' Fill the tabstops() array with the position of each tab stop.
        For i = 0 To sn.Fields.Count - 1
          accumtabstops = accumtabstops + biggest_value(i)
          tabstops(i + 1) = accumtabstops
        Next i
   
        ' numtabs must be a Long for Win32, Integer for Win16.
        numtabs = i
        ' Send LB_SETTABSTOP to the list box to set the position of each
        ' column.
   
        retval& = SendMessage(lb.hwnd, LB_SETTABSTOPS, numtabs, tabstops(1))
   
        ' Set the horizontal extent just wider than the first tab stop.
        ' This produces a horizontal scroll bar on the list box.
        ' This message requires coordinates in pixels, so we convert the tab
        ' stop coordinate back from dialog units to pixels.
   
        ' scrollbarwidth must be a Long for Win32, Integer for Win16
        scrollbarwidth = (tabstops(i) \ 4) * avgWidth
        retval& = SendMessage(lb.hwnd, LB_SETHORIZONTALEXTENT, _
                    scrollbarwidth, 0&)
   
        ' Restore form's original font property settings.
        Me.FontName = hold_fontname
        Me.FontSize = hold_fontsize
        Me.FontBold = hold_fontbold
        Me.FontItalic = hold_fontitalic
        Me.FontStrikethru = hold_fontstrikethru
        Me.FontUnderline = hold_fontunderline
      End Sub
   
   
      Private Sub Command1_Click()
        MousePointer = vbHourglass
        Dim db As Database
        Dim rs As Recordset
   
        Set db = DBEngine.Workspaces(0).OpenDatabase("BIBLIO.MDB")
        Set rs = db.OpenRecordset("Select * From Publishers", dbOpenSnapshot)
        Fill_List List1, rs
   
        rs.Close
        db.Close
        Set rs = Nothing
        Set db = Nothing
        MousePointer = vbDefault
      End Sub
   
   

4. Press the F5 key to run the program. Click the Fill List button. The list box now contains evenly spaced columns that display the contents of the Publishers table. The scroll bar enables you to see the entire line. Alter the NUMCHARS constant to allow more white space between columns if you want.