HOWTO: Arrange Order of List Items within ListBox Control

• Microsoft Visual Basic Enterprise Edition for Windows, version 5.0
• Microsoft Visual Basic Professional and Enterprise Editions, 16-bit and 32-bit, for Windows, version 4.0

SUMMARY

This article contains sample code that illustrates how to arrange the order of items within ListBox Control using drag-and-drop. Function ListRowCalc() returns the list index by calculating the position using the Windows API SendMessage() function with the constant LB_GETITEMHEIGHT and Screen.TwipsPerPixelY. Sub ListRowMove inserts the dragged item into the dropped position and re-orders all other affected items.

MORE INFORMATION

Step-by-Step Example

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

2. Add a module to the project. The default is Module1.

3. Paste the following code into the General Declarations section of Module1:

       #If Win16 Then
         Declare Function SendMessage& Lib "User" (ByVal hWnd%, ByVal _
                                     wMsg%, ByVal wParam%, lParam As Any)
       #Else
         Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
                        (ByVal hWnd As Long, ByVal wMsg As Long, _
                         ByVal wParam As Long, lParam As Long) As Long
       #End If
   
       Function ListRowCalc(lstTemp As Control, ByVal Y As Single) As Integer
          #If Win16 Then
              Const WM_USER = &H400
              Const LB_GETITEMHEIGHT = (WM_USER + 34)
          #Else
              Const LB_GETITEMHEIGHT = &H1A1
              'Determines the height of each item in ListBox control in pixels
          #End If
          Dim ItemHeight As Integer
          ItemHeight = SendMessage(lstTemp.hWnd, LB_GETITEMHEIGHT, 0, 0)
          ListRowCalc = min(((Y / Screen.TwipsPerPixelY)\ItemHeight)+ _
                        lstTemp.TopIndex, lstTemp.ListCount - 1)
       End Function
   
       Function min(X As Integer, Y As Integer) As Integer
            If X > Y Then min = Y Else min = X
       End Function
   
       Sub ListRowMove(lstTemp As Control, ByVal OldRow As Integer, _
                       ByVal NewRow As Integer)
           Dim SaveList As String, i As Integer
   
           If OldRow = NewRow Then Exit Sub
           SaveList = lstTemp.List(OldRow)
           If OldRow > NewRow Then
              For i = OldRow To NewRow + 1 Step -1
                  lstTemp.List(i) = lstTemp.List(i - 1)
              Next i
           Else
              For i = OldRow To NewRow - 1
                  lstTemp.List(i) = lstTemp.List(i + 1)
              Next i
           End If
           lstTemp.List(NewRow) = SaveList
       End Sub
   
   

4. Add a ListBox Control (List1) to Form1.

5. Clear all the code for Form1, and then paste the following code into the General Declarations section of Form1:

       Dim DragIndex As Integer
   

       Private Sub Form_Load()
           List1.Clear
           List1.AddItem "Adam"
           List1.AddItem "Bob"
           List1.AddItem "Charles"
           List1.AddItem "David"
           List1.AddItem "Eric"
           List1.AddItem "Frank"
           List1.AddItem "George"
       End Sub
   
       Private Sub List1_DragDrop(Source As Control, X As Single, Y As Single)
           ListRowMove Source, DragIndex, ListRowCalc(Source, Y)
       End Sub
   
       Private Sub List1_MouseDown(Button As Integer, Shift As Integer, _
                                  X As Single, Y As Single)
           If Button = vbRightButton Then
               DragIndex = ListRowCalc(List1, Y)
               List1.Drag
           End If
       End Sub
   
   

6. Assign an icon file to the DragIcon property of List1. Icon files are shipped with Visual Basic 4.0 under \ICONS directory.

7. From the Run menu, choose Start to run the program. Drag-and-drop any list item in List1 using the right-mouse button. The order of list items should be re-arranged accordingly.

REFERENCES

For additional information on how to drag-and-drop onto a list box, please see the following articles in the Microsoft Knowledge Base:

   ARTICLE-ID: Q80187
   TITLE     : How to Drop Item into Specified Location in VB List Box