Drag-and-drop

[JohnA]

OLV is great! However, I do not see how to implement drag-and-drop with it. I do not see it mentioned in the docs or in the sample app. Any ideas?

Thanks,
John

[JohnA]

Sure, here is all you need. In my example, I have a treeview (tvFolders) and an objectlistview (lvMessages). I want to drag-and-drop an item from the objectlistview onto the treeview and then move the file in question (class type=MyMessage)to the appropriate directory.

1) in the objectListView's ItemDrag event, put this:

DoDragDrop(objectListView.GetItem(objectListView.SelectedIndices(0)), DragDropEffects.Move)

2) in the treeview's DragOver event, put this:

    Dim pt As Point = CType(sender, TreeView).PointToClient(New Point(e.X, e.Y))
    Dim targetNode As TreeNode = tvFolders.GetNodeAt(pt)

    If targetNode IsNot Nothing Then
        If e.Data.GetDataPresent("BrightIdeasSoftware.OLVListItem", True) Then
            If Not tvFolders.SelectedNode Is targetNode Then
                If _lastHighlightedNode IsNot Nothing Then
                    _lastHighlightedNode.BackColor = Color.White
                End If
                targetNode.BackColor = Color.Yellow
                _lastHighlightedNode = targetNode

                Dim dropnode As TreeNode = CType(e.Data.GetData("System.Windows.Forms.TreeNode"), TreeNode)
                Do Until targetNode Is Nothing
                    If targetNode Is dropnode Then
                        e.Effect = DragDropEffects.None
                        Exit Sub
                    End If
                    targetNode = targetNode.Parent
                Loop
                e.Effect = DragDropEffects.Move
            End If
        End If
    Else
        e.Effect = DragDropEffects.None
        _lastHighlightedNode.BackColor = Color.White
    End If

3) In the treeview's DragDrop event, add this:

    _lastHighlightedNode.BackColor = Color.White

    If e.Data.GetDataPresent("BrightIdeasSoftware.OLVListItem", True) Then
        '-- move
        Dim strDetinationFolder As String = _lastHighlightedNode.Tag.ToString()
        Dim item As BrightIdeasSoftware.OLVListItem = CType(e.Data.GetData("BrightIdeasSoftware.OLVListItem"), BrightIdeasSoftware.OLVListItem)
        Dim strSource As String = CType(item.RowObject, MyMessage).Filename
        Dim strDestination As String = QualifyPath(strDetinationFolder) & System.IO.Path.GetFileName(strSource)
        System.IO.File.Move(strSource, strDestination)
        item.Remove()
        End If
    End If

4) Finally, in the treeview_DragEnter event, add this:

    If e.Data.GetDataPresent("BrightIdeasSoftware.OLVListItem", True) Then
        '-- move
        e.Effect = DragDropEffects.Move
    End If

5) Oh, you will also need this at the module level if you want to do some nice highlighting

Dim _lastHighlightedNode As TreeNode

[JohnA]

Actually, a little trial and error and I got drag-and-drop to work. I just needed to change my references to OLVListItem from "System.Windows.Forms.ListViewItem" and a few other minor tweaks but it works fine.

I bet others would love it if you updated the sample app to include drag-and-drop.

[Phillip Piper]

Hi John,

If you give me small example of how you made it work, I'll happily include it in the demo. Several people have asked for exactly this information, but I've never made it a priority to track it down.

Thanks,
Phillip

[Klaus]

I encountered an strange error:
Using simple drag and drop with OLV, this code does not work!


if (e.Data.GetDataPresent(typeof(OLVDataObject)))
e.Effect = DragDropEffects.Move;


What is more strange is that visual studio keeps insisting that the type of e.Data is actually OLVDataObject.

I had this same problem for another data object, but its solution is not applicable here. My other problem was that OLVDataObject was created in another DLL instance. Although the DLLs were exactly copies of themselves, the runtime type for the object was not the same. (string representations were exactly the same though!)

[Phillip Piper]

Hi Klaus,

When asking a question, it's generally better to create a new topic, rather than resurrecting a topic that is 6 years old! :)

Are you trying to move some OLV rows between two processes? That won't work.

e.Data is an instance of OLVDataObject -- it doesn't contain one.