Initiating drag from a TreeView

I am having difficulty in initiating a drag operation from my TreeView. This
seems like it should be a simple thing to accomplish but for the life of me I
can't figure it out. I'd expect there to be some methods to override like
OnDragBegin but I only see overrides for handling the drop operations (
OnDragEnter, OnDragOver, OnDrop ).

I'm guessing that I need to use DoDragDrop somewhere but I'm not sure where.
Do I need to handle mouse down/move and check to see if the user has started
to drag? I'd hope not - writing the same thing using straight Win32 is as
simple as handling the TVN_BEGINDRAG message. That way the OS handles the
drag delta checking.

I'm hoping this is something simple I'm overlooking-

Thanks-

John

John Dunn wrote:

> I am having difficulty in initiating a drag operation from my
> TreeView. This seems like it should be a simple thing to accomplish
> but for the life of me I can't figure it out. I'd expect there to be
> some methods to override like OnDragBegin but I only see overrides for
> handling the drop operations ( OnDragEnter, OnDragOver, OnDrop ).
>
> I'm guessing that I need to use DoDragDrop somewhere but I'm not sure
> where. Do I need to handle mouse down/move and check to see if the
> user has started to drag? I'd hope not - writing the same thing using
> straight Win32 is as simple as handling the TVN_BEGINDRAG message.
> That way the OS handles the drag delta checking.
>
> I'm hoping this is something simple I'm overlooking-

Have a look at this post[1] and this post[2]. They should answer your questions.

HTH,
Drew

[1] http://blogs.msdn.com/marcelolr/arch...02/542641.aspx
[2] http://blogs.msdn.com/marcelolr/arch...09/547923.aspx
___________________________________
Drew Marsh
Chief Software Architect
Mimeo.com, Inc. - http://www.mimeo.com
Microsoft C# / WPF MVP
Weblog - http://blog.hackedbrain.com/

Looking at those 2 posts it looks like it's up to me to handle the drag
detection. The problem is that TreeView::OnMouseDown only gets called when I
click on the background of the treeview and not when I click on a
TreeViewItem. It looks like it's possible to override
TreeViewItem::OnMouseDown - is that the correct way to go about this? It
seems odd that I need to derive from TreeViewItem just to get drag and drop
working but if that's what it takes then I guess I'll do it.

Thanks-

John

"Drew Marsh" wrote:

> John Dunn wrote:
>
> Have a look at this post[1] and this post[2]. They should answer your questions.
>
> HTH,
> Drew
>
> [1] http://blogs.msdn.com/marcelolr/arch...02/542641.aspx
> [2] http://blogs.msdn.com/marcelolr/arch...09/547923.aspx
> ___________________________________
> Drew Marsh
> Chief Software Architect
> Mimeo.com, Inc. - http://www.mimeo.com
> Microsoft C# / WPF MVP
> Weblog - http://blog.hackedbrain.com/
>
>
>

John Dunn wrote:

> Looking at those 2 posts it looks like it's up to me to handle the
> drag detection. The problem is that TreeView::OnMouseDown only gets
> called when I click on the background of the treeview and not when I
> click on a TreeViewItem. It looks like it's possible to override
> TreeViewItem::OnMouseDown - is that the correct way to go about this?
> It seems odd that I need to derive from TreeViewItem just to get drag
> and drop working but if that's what it takes then I guess I'll do it.

I believe it's because the mouse down event is being "handled" by the treeview
nodes. You need to listen for the routed event and handle "handled" events
too. Like so:

// The key here is the third parameter that indicates you want to be notified
about events even if they're handled already
this.myTreeView.AddHandler(Mouse.MouseDownEvent, new RoutedEventHandler(this.myTreeView_MouseDown),
true);


private void myTreeView_MouseDown(object source, RoutedEventArgs args)
{
TreeViewItem item = args.Source as TreeViewItem

if(item != null)
{
// Start your drag drop operation here
}
}

HTH,
Drew

Thanks - that did the trick!

"Drew Marsh" wrote:

> John Dunn wrote:
>
> > Looking at those 2 posts it looks like it's up to me to handle the
> > drag detection. The problem is that TreeView::OnMouseDown only gets
> > called when I click on the background of the treeview and not when I
> > click on a TreeViewItem. It looks like it's possible to override
> > TreeViewItem::OnMouseDown - is that the correct way to go about this?
> > It seems odd that I need to derive from TreeViewItem just to get drag
> > and drop working but if that's what it takes then I guess I'll do it.
>
> I believe it's because the mouse down event is being "handled" by the treeview
> nodes. You need to listen for the routed event and handle "handled" events
> too. Like so:
>
> // The key here is the third parameter that indicates you want to be notified
> about events even if they're handled already
> this.myTreeView.AddHandler(Mouse.MouseDownEvent, new RoutedEventHandler(this.myTreeView_MouseDown),
> true);
>
>
> private void myTreeView_MouseDown(object source, RoutedEventArgs args)
> {
> TreeViewItem item = args.Source as TreeViewItem
>
> if(item != null)
> {
> // Start your drag drop operation here
> }
> }
>
> HTH,
> Drew
>
>
>