Question

I have several listboxes in a form that I can drag and drop items between. The drag and drop part of the code seems to work fine. Upon dropping an item into a listbox, I have a listbox resize procedure go through and resize the listboxes to fit their contents. The problem that I am running into is that upon dragging an item from LB1 (for example) to LB2, LB1 resizes as if it had one extra item in it’s list. I would like to prevent that, but I’m not sure how. Here’s the resize code:

    Private Sub ListBox_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles ListBox1.MouseDown, ListBox2.MouseDown

    Dim Lbx As ListBox = sender
    Dim Pt As New Point(e.X, e.Y) ' Returns coords of mouse 
    Dim Idx As Integer
    Dim retval As DragDropEffects

    ' Determine which listbox item was dragged 
    Idx = Lbx.IndexFromPoint(Pt)

    ' Start a Drag and drop with that item 
    If Idx >= 0 Then
        ' 
        retval = Lbx.DoDragDrop(Lbx.Items(Idx), DragDropEffects.All)
        Debug.WriteLine(retval)
        If retval And DragDropEffects.Move Then
            Lbx.Items.RemoveAt(Idx)
        End If
    End If

End Sub

Private Sub ListBox_DragEnter(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles ListBox1.DragEnter, ListBox2.DragEnter
    If (e.Data.GetDataPresent(DataFormats.Text)) Then
        e.Effect = DragDropEffects.Move Or DragDropEffects.Copy
    End If
End Sub


Private Sub ListBox_DragDrop(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles ListBox1.DragDrop, ListBox2.DragDrop
    Dim LB As ListBox = sender
    LB.Items.Add(e.Data.GetData("Text"))
    QueueResize()
End Sub

And here is the code for the resize:

    Private Sub QueueResize()
    For Each cont As System.Windows.Forms.Control In Panel1.Controls
        If cont.GetType.ToString = "System.Windows.Forms.ListBox" Then

            Dim LB As ListBox = cont
            On Error GoTo ErrHandler

            Dim lItemHeight As Long
            Dim lRet As Long
            Dim lItems As Long
            Dim sngTwips As Single
            Dim sngLBHeight As Single

            If LB.Items.Count = 0 Then
                LB.Height = 25
                'Return True

            Else
                lItems = LB.Items.Count

                lItemHeight = LB.ItemHeight
                If lItemHeight > 0 Then
                    LB.Height = lItemHeight * lItems + 5
                    'AutoSizeLBHeight = True
                End If
            End If
        End If
    Next
ErrHandler:
End Sub

Any help would be appreciated! Thanks in advance.

Answer 1

Add two List View controls to a form.
Set the AllowDrop property of each List View control to true.
Set the MultiSelect property of each List View control to true.
Set the View property of each List View control to List.
Add the following code:

Public Class Form1

Private Sub ListView1_DragDrop(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles ListView1.DragDrop, ListView2.DragDrop
    Dim myItem As ListViewItem
    Dim myItems() As ListViewItem = e.Data.GetData("System.Windows.Forms.ListViewItem()")
    Dim i As Integer = 0

    For Each myItem In myItems
        ' Add the item to the target list.
        sender.Items.Add(myItems(i).Text)
        ' Remove the item from the source list.
        If sender Is ListView1 Then
            ListView2.Items.Remove(ListView2.SelectedItems.Item(0))
        Else
            ListView1.Items.Remove(ListView1.SelectedItems.Item(0))
        End If
        i = i + 1
    Next
End Sub

Private Sub ListView1_DragEnter(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles ListView1.DragEnter, ListView2.DragEnter
    ' Check for the custom DataFormat ListViewItem array.
    If e.Data.GetDataPresent("System.Windows.Forms.ListViewItem()") Then
        e.Effect = DragDropEffects.Move
    Else
        e.Effect = DragDropEffects.None
    End If
End Sub

Private Sub ListView1_ItemDrag(ByVal sender As System.Object, ByVal e As System.Windows.Forms.ItemDragEventArgs) Handles ListView2.ItemDrag, ListView1.ItemDrag
    Dim myItem As ListViewItem
    Dim myItems(sender.SelectedItems.Count - 1) As ListViewItem
    Dim i As Integer = 0

    ' Loop though the SelectedItems collection for the source.
    For Each myItem In sender.SelectedItems
        ' Add the ListViewItem to the array of ListViewItems.
        myItems(i) = myItem
        i = i + 1
    Next
    ' Create a DataObject containg the array of ListViewItems.
    sender.DoDragDrop(New  _
    DataObject("System.Windows.Forms.ListViewItem()", myItems), _
    DragDropEffects.Move)
End Sub

End Class