Listbox problems

**Robin Tucker** · Nov 21 '05, 06:32 PM

Re: Listbox problems

You are just effecitvely changing the index of the source item, ie. it's
location in the set. To do this yes you should delete the source item. It
won't actually be "deleted", because of course your drag/drop still holds a
reference to it. In order to discover the correct placement position, you
need to use the IndexFromPoint method, passing in the mouse coords.

There is an MSDN example using drag/drop here:

http://msdn.microsoft.com/library/de...pointtopic.asp

"John Dann" <news@prodata.c o.uk> wrote in message
news:n83db1l736 96obkpf9g32l97d oe4af1l3m@4ax.c om...[color=blue]
> [Originally posted to m.p.d.l.v.windo wsforms.control s but seems to be
> v low traffic there, so hope no-one minds if I repost here.]
>
> I'm still struggling to find a way of reordering the items within the
> same single listbox with drag and drop. I think I've got the drag
> working but it's the drop code I can't figure out. What I have
> currently is (with the listbox set to AllowDrop):
>
> Sub MyListBox_Mouse Down(args etc...)
> DoDragDrop(MyLi stBox.SelectedI tem, DragDropEffects .Move)
> End Sub
>
> Sub MyListBox_DragE nter(args etc...)
> e.effect=DragDr opEffects.Move
> End sub
>
> Sub MyListBox.DragD rop(args etc...)
> 'Here's where I'm stuck! Presumably I need:
> MyListBox.Items .Insert(???, MyListBox.Selec tedItem)
> End Sub
>
> Obviously I need some code in the last sub to insert the
> currently-selected item (ie the one picked up by the Drag) immediately
> before the item over which the mouse is currently hovering. But how
> can I get the index of this item and then drop the selected item.
> Possibly/probably I need to explicitly delete the source item?
>
> Thanks for any help.
> JGD[/color]

**John Dann** · Nov 21 '05, 06:32 PM

Re: Listbox problems

OK, many thanks - I'm making some progress I think, but it's not
working yet. I seem to be able to drag an item (or at least the faint
grey dragging rectangle appears as the cursor), but the final step of
performing the insert isn't there yet. Here's the code I currently
have:

Private Sub lbxSelFields_Mo useDown(ByVal sender As Object, ByVal e As
System.Windows. Forms.MouseEven tArgs) Handles lbxSelFields.Mo useDown
Dim lb As ListBox = CType(sender, ListBox)
Dim pt As New Point(e.X, e.Y)
Dim index As Integer = lb.IndexFromPoi nt(pt)
If index >= 0 Then
lb.DoDragDrop(l b.Items(index). ToString(),
DragDropEffects .Move)
End If
End Sub

Private Sub lbxSelFields_Dr agEnter(ByVal sender As Object, ByVal e
As System.Windows. Forms.DragEvent Args) Handles lbxSelFields.Dr agEnter
If e.Data.GetDataP resent(GetType( String)) Then
e.Effect = DragDropEffects .Move
Else
e.Effect = DragDropEffects .None
End If
End Sub

Private Sub lbxSelFields_Dr agDrop(ByVal sender As Object, ByVal e
As System.Windows. Forms.DragEvent Args) Handles lbxSelFields.Dr agDrop
Dim lb As ListBox = CType(sender, ListBox)
Dim pt As New Point(e.X, e.Y)
Dim index As Integer = lb.IndexFromPoi nt(pt)
lbxSelFields.It ems.Insert(inde x,
e.Data.GetData( "System.string" , True).ToString( ))
End Sub

This is cobbled together from 2 or 3 examples and so maybe I'm
incorrectly mixing some parameters/variables. I'm not sure why for
example I should make the declaration:

Dim lb As ListBox = CType(sender, ListBox)

when the control itself is a listbox. Could I just say in eg internal
line 3 of the MouseDown procedure:

Dim index As Integer = lbxSelFields.In dexFromPoint(pt )

But most importantly why wouldn't the lbxSelFields.It ems.Insert(...)
line in the DragDrop event be working?

Thanks
JGD

**Robin Tucker** · Nov 21 '05, 06:32 PM

Re: Listbox problems

Check the index value to make sure it is valid firstly. Although I'm sure
you would get an indexoutofrange exception if it was something like -1.
Also, did you set the "AllowDrop" property of the list box?

You don't need to write, CType(sender, ListBox), it's just an alternative
way of looking at things. You can explicitly use your list box name if you
like in that method.

"John Dann" <news@prodata.c o.uk> wrote in message
news:ua7db1t67i aq9f49t6g928rh4 gna19ao80@4ax.c om...[color=blue]
> OK, many thanks - I'm making some progress I think, but it's not
> working yet. I seem to be able to drag an item (or at least the faint
> grey dragging rectangle appears as the cursor), but the final step of
> performing the insert isn't there yet. Here's the code I currently
> have:
>
> Private Sub lbxSelFields_Mo useDown(ByVal sender As Object, ByVal e As
> System.Windows. Forms.MouseEven tArgs) Handles lbxSelFields.Mo useDown
> Dim lb As ListBox = CType(sender, ListBox)
> Dim pt As New Point(e.X, e.Y)
> Dim index As Integer = lb.IndexFromPoi nt(pt)
> If index >= 0 Then
> lb.DoDragDrop(l b.Items(index). ToString(),
> DragDropEffects .Move)
> End If
> End Sub
>
> Private Sub lbxSelFields_Dr agEnter(ByVal sender As Object, ByVal e
> As System.Windows. Forms.DragEvent Args) Handles lbxSelFields.Dr agEnter
> If e.Data.GetDataP resent(GetType( String)) Then
> e.Effect = DragDropEffects .Move
> Else
> e.Effect = DragDropEffects .None
> End If
> End Sub
>
> Private Sub lbxSelFields_Dr agDrop(ByVal sender As Object, ByVal e
> As System.Windows. Forms.DragEvent Args) Handles lbxSelFields.Dr agDrop
> Dim lb As ListBox = CType(sender, ListBox)
> Dim pt As New Point(e.X, e.Y)
> Dim index As Integer = lb.IndexFromPoi nt(pt)
> lbxSelFields.It ems.Insert(inde x,
> e.Data.GetData( "System.string" , True).ToString( ))
> End Sub
>
> This is cobbled together from 2 or 3 examples and so maybe I'm
> incorrectly mixing some parameters/variables. I'm not sure why for
> example I should make the declaration:
>
> Dim lb As ListBox = CType(sender, ListBox)
>
> when the control itself is a listbox. Could I just say in eg internal
> line 3 of the MouseDown procedure:
>
> Dim index As Integer = lbxSelFields.In dexFromPoint(pt )
>
> But most importantly why wouldn't the lbxSelFields.It ems.Insert(...)
> line in the DragDrop event be working?
>
> Thanks
> JGD[/color]

**Robin Tucker** · Nov 21 '05, 06:32 PM

Re: Listbox problems

Ahhh sorry, also forgot to mention you need to convert the coords to client
relative coords first when dropping, as you get screen relative coords from
the DragDrop method, like this:

Private Sub ListBox1_DragDr op(ByVal sender As Object, ByVal e As
DragEventArgs) Handles ListBox1.DragDr op

Dim thePoint As New Point(e.X, e.Y)

thePoint = ListBox1.PointT oClient(thePoin t)

Dim index As Integer = ListBox1.IndexF romPoint(thePoi nt)

If index >= 0 Then
ListBox1.Items. Insert(index, e.Data.GetData( "System.String" ,
True).ToString( ))
End If

End Sub

"John Dann" <news@prodata.c o.uk> wrote in message
news:ua7db1t67i aq9f49t6g928rh4 gna19ao80@4ax.c om...[color=blue]
> OK, many thanks - I'm making some progress I think, but it's not
> working yet. I seem to be able to drag an item (or at least the faint
> grey dragging rectangle appears as the cursor), but the final step of
> performing the insert isn't there yet. Here's the code I currently
> have:
>
> Private Sub lbxSelFields_Mo useDown(ByVal sender As Object, ByVal e As
> System.Windows. Forms.MouseEven tArgs) Handles lbxSelFields.Mo useDown
> Dim lb As ListBox = CType(sender, ListBox)
> Dim pt As New Point(e.X, e.Y)
> Dim index As Integer = lb.IndexFromPoi nt(pt)
> If index >= 0 Then
> lb.DoDragDrop(l b.Items(index). ToString(),
> DragDropEffects .Move)
> End If
> End Sub
>
> Private Sub lbxSelFields_Dr agEnter(ByVal sender As Object, ByVal e
> As System.Windows. Forms.DragEvent Args) Handles lbxSelFields.Dr agEnter
> If e.Data.GetDataP resent(GetType( String)) Then
> e.Effect = DragDropEffects .Move
> Else
> e.Effect = DragDropEffects .None
> End If
> End Sub
>
> Private Sub lbxSelFields_Dr agDrop(ByVal sender As Object, ByVal e
> As System.Windows. Forms.DragEvent Args) Handles lbxSelFields.Dr agDrop
> Dim lb As ListBox = CType(sender, ListBox)
> Dim pt As New Point(e.X, e.Y)
> Dim index As Integer = lb.IndexFromPoi nt(pt)
> lbxSelFields.It ems.Insert(inde x,
> e.Data.GetData( "System.string" , True).ToString( ))
> End Sub
>
> This is cobbled together from 2 or 3 examples and so maybe I'm
> incorrectly mixing some parameters/variables. I'm not sure why for
> example I should make the declaration:
>
> Dim lb As ListBox = CType(sender, ListBox)
>
> when the control itself is a listbox. Could I just say in eg internal
> line 3 of the MouseDown procedure:
>
> Dim index As Integer = lbxSelFields.In dexFromPoint(pt )
>
> But most importantly why wouldn't the lbxSelFields.It ems.Insert(...)
> line in the DragDrop event be working?
>
> Thanks
> JGD[/color]

**John Dann** · Nov 21 '05, 06:33 PM

Re: Listbox problems

Thanks again - making progress but not there yet:

I can now get a sensible index value in the DragDrop event, but the
overall process isn't working yet. As a next step I'd like to make
sure that I'm actually picking up a value in the initial MouseDown
event.

What I was now hoping to do here was to pick up an index value of the
list item on which the mouse button was pressed at the start of the
drag operation.

Private Sub lbxSelFields_Mo useDown(ByVal sender As Object, ByVal e As
System.Windows. Forms.MouseEven tArgs) Handles lbxSelFields.Mo useDown
Dim pt As New Point(e.X, e.Y)
pt=lbxSelFields .PointToClient( pt)
Dim index As Integer = lbxSelFields.In dexFromPoint(pt )

' For investigation insert:
msgbox("Index = " & index.tostring)

If index >= 0 Then
lb.DoDragDrop(l b.Items(index). ToString(),
DragDropEffects .Move)
End If
End Sub

But the value of Index stays resolutely at -1. Looks like the final pt
values are not mapping to a valid item on the list. But I can't spot
the flaw. OR maybe I can't use this same process in the MouseDown as
in the DragDrop events?

JGD

**Robin Tucker** · Nov 21 '05, 06:33 PM

Re: Listbox problems

The thing is, when you get the MouseDown event, it's relative to the list,
so no need to "PointToCli ent" there.... But in the DragDrop event, the
PointToClient is required. Don't ask me why ;) So.....

Private Sub lbxSelFields_Mo useDown(ByVal sender As Object, ByVal e As
System.Windows. Forms.MouseEven tArgs) Handles lbxSelFields.Mo useDown

Dim index As Integer = lbxSelFields.In dexFromPoint(e. X, e.Y)

' For investigation insert:

msgbox("Index = " & index.tostring)

If index >= 0 Then
lb.DoDragDrop(l b.Items(index). ToString(), DragDropEffects .Move)
End If

End Sub

"John Dann" <news@prodata.c o.uk> wrote in message
news:v4ddb1l5dv ro97lds7v0sbbk1 6djj9c859@4ax.c om...[color=blue]
> Thanks again - making progress but not there yet:
>
> I can now get a sensible index value in the DragDrop event, but the
> overall process isn't working yet. As a next step I'd like to make
> sure that I'm actually picking up a value in the initial MouseDown
> event.
>
> What I was now hoping to do here was to pick up an index value of the
> list item on which the mouse button was pressed at the start of the
> drag operation.
>
> Private Sub lbxSelFields_Mo useDown(ByVal sender As Object, ByVal e As
> System.Windows. Forms.MouseEven tArgs) Handles lbxSelFields.Mo useDown
> Dim pt As New Point(e.X, e.Y)
> pt=lbxSelFields .PointToClient( pt)
> Dim index As Integer = lbxSelFields.In dexFromPoint(pt )
>
> ' For investigation insert:
> msgbox("Index = " & index.tostring)
>
> If index >= 0 Then
> lb.DoDragDrop(l b.Items(index). ToString(),
> DragDropEffects .Move)
> End If
> End Sub
>
> But the value of Index stays resolutely at -1. Looks like the final pt
> values are not mapping to a valid item on the list. But I can't spot
> the flaw. OR maybe I can't use this same process in the MouseDown as
> in the DragDrop events?
>
> JGD[/color]

**John Dann** · Nov 21 '05, 06:33 PM

Re: Listbox problems

Thanks again for your help and progress, progress, but not quite
success ye!. I'm now getting valid indices for both source and target
items, but still nothing seems to be happening at the final drop.

The relevant procedures are now as follows:

Private Sub lbxSelFields_Mo useDown(ByVal sender As Object, ByVal e
As System.Windows. Forms.MouseEven tArgs) Handles lbxSelFields.Mo useDown
lbxSelFields.Al lowDrop() = True
Dim pt As New Point(e.X, e.Y)
Dim itemindex As Integer = lbxSelFields.In dexFromPoint(pt )
If itemindex >= 0 Then
Me.Text = "Source Index = " & itemindex.ToStr ing()

lbxSelFields.Do DragDrop(lbxSel Fields.Items(it emindex).ToStri ng(),
DragDropEffects .Move)
End If
End Sub

Private Sub lbxSelFields_Dr agEnter(ByVal sender As Object, ByVal e
As System.Windows. Forms.DragEvent Args) Handles lbxSelFields.Dr agEnter
If e.Data.GetDataP resent(GetType( String)) Then
e.Effect = DragDropEffects .Move
Else
e.Effect = DragDropEffects .None
End If
End Sub

Private Sub lbxSelFields_Dr agDrop(ByVal sender As Object, ByVal e
As System.Windows. Forms.DragEvent Args) Handles lbxSelFields.Dr agDrop
Dim pt As New Point(e.X, e.Y)
pt = lbxSelFields.Po intToClient(pt)
Dim itemindex As Integer = lbxSelFields.In dexFromPoint(pt )
Me.Text = "Target Index = " & itemindex.ToStr ing()
lbxSelFields.It ems.Insert(item index,
e.Data.GetData( "System.string" , True).ToString( ))
End Sub

I'm left with three thoughts as to what the remaining problem might
be:

1. Some key line of code or setting has been omitted;

2. There's something not right with the way the item string that is to
be moved is formatted or configured. ie that is to be inserted via the
e.Data.GetData( "System.string" , True).ToString( ) string, which I must
admit I don't fully understand.

3. There's some particular problem or trick to do with the fact that I
want to drag within the same listbox rather than from one control to
another.

JGD

**Robin Tucker** · Nov 21 '05, 06:33 PM

Re: Listbox problems

Okay, what the call to "GetData" does is ask the object for a format of type
"System.str ing" - as basically these objects implement an interface called
IDataObject and in theory, they can present their data to you in many
different formats (perhaps a table if dragging into Excel or Word for
instance, different formats according to what is being dragged). So, you
are asking the object if it can give you it's data in string format. If it
can, it will return it, otherwise it will return nothing. I have a feeling
if you try GetData("System .String") it will work as I think it's case
sensitive.

"John Dann" <news@prodata.c o.uk> wrote in message
news:99jdb1llf8 hsn374f1s4t6jij mjj0tf0t2@4ax.c om...[color=blue]
> Thanks again for your help and progress, progress, but not quite
> success ye!. I'm now getting valid indices for both source and target
> items, but still nothing seems to be happening at the final drop.
>
> The relevant procedures are now as follows:
>
> Private Sub lbxSelFields_Mo useDown(ByVal sender As Object, ByVal e
> As System.Windows. Forms.MouseEven tArgs) Handles lbxSelFields.Mo useDown
> lbxSelFields.Al lowDrop() = True
> Dim pt As New Point(e.X, e.Y)
> Dim itemindex As Integer = lbxSelFields.In dexFromPoint(pt )
> If itemindex >= 0 Then
> Me.Text = "Source Index = " & itemindex.ToStr ing()
>
> lbxSelFields.Do DragDrop(lbxSel Fields.Items(it emindex).ToStri ng(),
> DragDropEffects .Move)
> End If
> End Sub
>
> Private Sub lbxSelFields_Dr agEnter(ByVal sender As Object, ByVal e
> As System.Windows. Forms.DragEvent Args) Handles lbxSelFields.Dr agEnter
> If e.Data.GetDataP resent(GetType( String)) Then
> e.Effect = DragDropEffects .Move
> Else
> e.Effect = DragDropEffects .None
> End If
> End Sub
>
> Private Sub lbxSelFields_Dr agDrop(ByVal sender As Object, ByVal e
> As System.Windows. Forms.DragEvent Args) Handles lbxSelFields.Dr agDrop
> Dim pt As New Point(e.X, e.Y)
> pt = lbxSelFields.Po intToClient(pt)
> Dim itemindex As Integer = lbxSelFields.In dexFromPoint(pt )
> Me.Text = "Target Index = " & itemindex.ToStr ing()
> lbxSelFields.It ems.Insert(item index,
> e.Data.GetData( "System.string" , True).ToString( ))
> End Sub
>
> I'm left with three thoughts as to what the remaining problem might
> be:
>
> 1. Some key line of code or setting has been omitted;
>
> 2. There's something not right with the way the item string that is to
> be moved is formatted or configured. ie that is to be inserted via the
> e.Data.GetData( "System.string" , True).ToString( ) string, which I must
> admit I don't fully understand.
>
> 3. There's some particular problem or trick to do with the fact that I
> want to drag within the same listbox rather than from one control to
> another.
>
> JGD[/color]

**John Dann** · Nov 21 '05, 06:34 PM

Re: Listbox problems

On Mon, 20 Jun 2005 18:33:23 +0100, "Robin Tucker"
<idontwanttobes pammedanymore@r eallyidont.com> wrote:
[color=blue]
>I have a feeling
>if you try GetData("System .String") it will work as I think it's case
>sensitive.
>[/color]
Yes indeed, that was exactly the problem. I guess I should have let
the Intellisense write it rather than a human!

Almost there now, but one remaining problem which is how to delete the
original listbox item at its original position. I've been trying a
variety of approaches but none seems to work properly - they either
remove two items (maybe because an event is being fired twice?) or
none! It seems a little like other aspects of this particular problem
in that only exactly the right solution will work robustly.

I'm continuing to experiment, but if Robin or anyone can suggest the
best removal solution then that would be incredibly welcome. Really
there are two questions:

1. Should the removal of the original item at its pre-move position be
done in the MouseDown or DragDrop events?

2. What's the best removel method to use, by index, selected item or
what?

Thanks
JGD

**Robin Tucker** · Nov 21 '05, 06:34 PM

Re: Listbox problems

Do it in the drag drop event, before you insert the "dropped" item, that way
you know the item to delete still has the same index.

"John Dann" <news@prodata.c o.uk> wrote in message
news:8pdfb1ldj1 img2j19mvetqui0 568c7tjck@4ax.c om...[color=blue]
> On Mon, 20 Jun 2005 18:33:23 +0100, "Robin Tucker"
> <idontwanttobes pammedanymore@r eallyidont.com> wrote:
>[color=green]
>>I have a feeling
>>if you try GetData("System .String") it will work as I think it's case
>>sensitive.
>>[/color]
> Yes indeed, that was exactly the problem. I guess I should have let
> the Intellisense write it rather than a human!
>
> Almost there now, but one remaining problem which is how to delete the
> original listbox item at its original position. I've been trying a
> variety of approaches but none seems to work properly - they either
> remove two items (maybe because an event is being fired twice?) or
> none! It seems a little like other aspects of this particular problem
> in that only exactly the right solution will work robustly.
>
> I'm continuing to experiment, but if Robin or anyone can suggest the
> best removal solution then that would be incredibly welcome. Really
> there are two questions:
>
> 1. Should the removal of the original item at its pre-move position be
> done in the MouseDown or DragDrop events?
>
> 2. What's the best removel method to use, by index, selected item or
> what?
>
> Thanks
> JGD[/color]

**John Dann** · Nov 21 '05, 06:34 PM

Re: Listbox problems

On Tue, 21 Jun 2005 12:32:53 +0100, "Robin Tucker"
<idontwanttobes pammedanymore@r eallyidont.com> wrote:
[color=blue]
>Do it in the drag drop event, before you insert the "dropped" item, that way
>you know the item to delete still has the same index.
>[/color]

OK many thanks for that.

But sadly there's a sting in the tail still. While the drag/drop
procedure now works fine, another procedure relating to the same
listbox that responded to the listbox_DoubleC lick event (to delete an
item) no longer works. I guess what may be happening is that any mouse
click on the listbox is raising a MouseDown event and maybe this
blocks out other event handlers?

So I'm left with another question, ie is there any way to make the
pre-Drag Mousedown procedure more selective or somehow to turn it on
and off?

For anyone that may look at this thread in future, the overall code
I've ended up with for moving items up and down a listbox with the
mouse is as follows:

' Form declarations
Dim PreMoveIndex as Integer

Private Sub lbxSelFields_Mo useDown(ByVal sender As Object, ByVal e As
System.Windows. Forms.MouseEven tArgs) Handles lbxSelFields.Mo useDown
Dim pt As New Point(e.X, e.Y)
PreMoveIndex = lbxSelFields.In dexFromPoint(pt )
If PreMoveIndex >= 0 Then

lbxSelFields.Do DragDrop(lbxSel Fields.Items(Pr eMoveIndex).ToS tring(),
DragDropEffects .Move)
End If
End Sub

Private Sub lbxSelFields_Dr agEnter(ByVal sender As Object, ByVal e
As System.Windows. Forms.DragEvent Args) Handles lbxSelFields.Dr agEnter
If e.Data.GetDataP resent(GetType( String)) Then
e.Effect = DragDropEffects .Move
Else
e.Effect = DragDropEffects .None
End If
End Sub

Private Sub lbxSelFields_Dr agDrop(ByVal sender As Object, ByVal e
As System.Windows. Forms.DragEvent Args) Handles lbxSelFields.Dr agDrop
Dim pt As New Point(e.X, e.Y)
pt = lbxSelFields.Po intToClient(pt)
Dim PostMoveIndex as Integer = lbxSelFields.In dexFromPoint(pt )
lbxSelFields.It ems.RemoveAt(Pr eMoveIndex)
lbxSelFields.It ems.Insert(Post MoveIndex,
e.Data.GetData( "System.String" , True).ToString( ))
End Sub

JGD

Listbox problems

Listbox problems

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