Welcome to the premier issue of Code of the Week for Visual Basic. You have found what promises to be the best source code resource for your Visual Basic development.
The source code in this issue is designed for Visual Basic 4.0 16-bit. Similiar code can be implemented in the 32-bit versions of VB. Only the module declarations for the API call should need to be changed. If you are interested in seeing this code, please contact us at http://www.codeoftheweek.com/feedback.html
In this issue we are going to introduce a object class called cListBoxDragDrop. You can use this class to allow your end-users to rearrange the data in a standard Windows list box.
Add drag and drop rearranging/sorting to a standard Windows list box. There are several important methods in the class.
To use this example, create a new project in Visual Basic 4.0 16-bit and drop a list box on a form. Change the Name property of the list box to lstWords. Paste the following code into the declarations section of the form.
Option Explicit
Dim oListDrag As New cListBoxDragDrop
Private Sub Form_Load()
Set oListDrag.FormObj = Me
Set oListDrag.ListBoxObj = lstWords
End Sub
Private Sub lstWords_MouseDown(Button As Integer, Shift As Integer, x As Single, Y As Single)
' Traps the Mouse Down event which will start
' the dragging operation.
oListDrag.MouseDown
End Sub
Private Sub lstWords_MouseUp(Button As Integer, Shift As Integer, x As Single, Y As Single)
' Traps the MouseUp event which will end
' the dragging operation.
oListDrag.MouseUp
End Sub
Private Sub lstWords_MouseMove(Button As Integer, Shift As Integer, x As Single, Y As Single)
' Traps the MouseMove event which will show the
' item in the list being dragged around.
oListDrag.DoDragDrop x, Y
End Sub
Option Explicit
' Declaration for the API call to get the top index in the Listbox.
Private Declare Function SendMessage& Lib "User" (ByVal hWnd%, ByVal _
wMsg%, ByVal wParam%, lParam As Any)
Const LB_GETTOPINDEX = &H400 + 15
' Pointer to the actual listbox that going to have drag and drop
' actions performed on it.
Dim mlstDragDrop As ListBox
' Form that contains the listbox we are acting on.
Dim mfrmObj As Form
' Text of the item that is being dragged
Dim msDraggedItem As String
' Last index in the listbox of the item that is being dragged
' within the list. We need to remember this so that
' we don't do unneccesary moves during the MouseMove
' event.
Dim mlLastPos As Long
Public Sub MouseDown()
' Start our drag action. Change pointer and remember
' item being moved
msDraggedItem = ListBoxObj.List(ListBoxObj.ListIndex)
' use custom pointer if you specify your own icon in
' the MouseIcon property.
'FormObj.MousePointer = 99
FormObj.MousePointer = 2 ' cross hair
mlLastPos = ListBoxObj.ListIndex
End Sub
Public Property Get ListBoxObj() As ListBox
Set ListBoxObj = mlstDragDrop
End Property
Public Property Set ListBoxObj(lstBox As ListBox)
Set mlstDragDrop = lstBox
End Property
Public Property Get FormObj() As Form
Set FormObj = mfrmObj
End Property
Public Property Set FormObj(frm As Form)
Set mfrmObj = frm
' You can specify your own MousePointer for the
' Drag and Drop operation here. If you set this
' be sure to change the code in MouseDown to
' set MousePointer to 99 (custom pointer)
' The Point02.ico file that comes with VB in the
' icons directory is a pretty good pointer
' icon.
'frm.MouseIcon = LoadPicture("Point02.ico")
End Property
' This call should be put into the MouseUp event of the list box
' that is performing drag and drop.
Public Sub MouseUp()
msDraggedItem = "" ' done dragging, "forget" item
FormObj.MousePointer = vbDefault ' return pointer to default pointer
mlLastPos = ListBoxObj.ListIndex ' remember the last position we are
' at in the list box
End Sub
' This call should be put into the MouseMove event of the list box
' that is performing drag and drop.
Public Sub DoDragDrop(x As Single, Y As Single)
Dim iTop As Integer, iInsert As Single
Dim lNewPos As Long
Dim lRowHeight As Long
' figure out the index of the top most element in the list box
iTop = SendMessage(ListBoxObj.hWnd, LB_GETTOPINDEX, 0&, 0&)
' calculate the height of a single row in the list box
lRowHeight = FormObj.TextHeight("X")
' figure out which row we are at
iInsert = Y \ lRowHeight
' if we haven't moved to a new row yet, just exit
If mlLastPos = ListBoxObj.ListIndex Then
Exit Sub
End If
' calculate the new index to insert the item being dragged
lNewPos = iInsert + iTop
If lNewPos < 0 Then
lNewPos = 0
End If
If lNewPos >= ListBoxObj.ListCount Then
lNewPos = ListBoxObj.ListCount - 1
End If
' if we have an item, move it to the new position
' take care of case when moving item up or down in list
If Len(msDraggedItem) >= 1 Then
If mlLastPos < ListBoxObj.ListIndex Then
ListBoxObj.RemoveItem mlLastPos
If lNewPos >= ListBoxObj.ListCount Then
ListBoxObj.AddItem msDraggedItem
Else
ListBoxObj.AddItem msDraggedItem, lNewPos
End If
mlLastPos = ListBoxObj.NewIndex
Else
ListBoxObj.RemoveItem mlLastPos
ListBoxObj.AddItem msDraggedItem, lNewPos
mlLastPos = ListBoxObj.NewIndex
End If
End If
End Sub
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