Bruno,
> Chris I can't find that mail. And it is not in Deja news.
(BTW. Ian Bartholomew's news-group archive at
http://www.iandb.org.uk/is an excellent resource for any Dolphin programmer, I strongly recommed
you download it)
I've mailed you a copy of my post to you directly, but there's some
other stuff I want to add here.
In that post, I talked about how to connect up the D&D operations in a
Presenter, so I was assuming that the View was already doing it's part
of the job -- which is true when you are using the standard View
components.
What I hadn't really noticed is that you are attempting to add D&D to
the Playground app, which uses a custom View, so there is some more work
to be done to get D&D working.
I haven't done much messing around with custom Views -- in fact I wrote
my first only last week -- but it doesn't *seem* to be too difficult. I
used the MoenTreeView as a guide to put together the following. If
anyone knows of anything I've missed or done wrong/poorly then please
tell us!
We'll have to add a couple of methods: Playground>>onLeftButtonPressed:
and Playgound>>requestDragObjects:, and copy #dragDetect: from
MoenTreeView.
First, we need to start a drag-drop session when someone attempts to
drag one of the objects out of the playgound. That is accomplished by
adding a method like:
----------
onLeftButtonPressed: aMouseEvent
| target |
target := shapes at: 1 ifAbsent: [nil]. "just to demo, pick a shape
at random"
(self isDragSource and: [target notNil and: [self dragDetect:
aMouseEvent]])
ifTrue: [self onBegin: aMouseEvent button drag: target].
^ super onLeftButtonPressed: aMouseEvent.
---------
Here, I just choose an object to drag at random. A (much!) better
version would probably do something like picking the object under the
mouse, or the "current selection" if Playgound had a concept of
selection.
I'm using #dragDetect: here to see if the user is begining a drag
operation. I've just copied MoenTreeView>>dragDetect: into Playgound.
(If anyone at OA is reading, would it be a good idea to move dragDetect:
up into View ? It seems generally usefull)
That object is used to start a drag-drop session. The session responds
by asking the View (and in turn the Presenter) to fill in its details.
It sends #requestDragObjects: to the View, so we need to add a second
method like:
---------
requestDragObjects: session
| target |
target := session suggestedSource.
target isNil ifFalse: [session addDragObject:
(InternalDragDropObject object: target)].
^ super requestDragObjects: session.
---------
This is expected to initialise the set of drag-objects in the session
with the View's best guess at what's appropriate (the Presenter will get
a chance to modify it more intelligently later, as I described in my
earlier post).
I'm having to do something rather odd in the above code, and I'm not
sure if that's because I'm missing something, or there's a flaw in the
design of this part of the D&D system. The View is expected to fill in
the drag objects (remember that there may be more than one, in general),
but #requestDragObjects: doesn't have enough information to be able to
do that properly in this case. If Playgound had a concept of a
"current-selection" (as ListViews, and MoenTreeView, etc, do) then it'd
be natural to add any selected shapes to the sesssion. But since it
doesn't have that concept, the proper thing to do would probably be to
add the object under the mouse. Unfortunately, at this point we don't
know where the mouse was when the user started the operation. What I
have done is to use the #suggestedSource of the D&D session (which was
set earlier when I did #self onBegin:drag:). It's more than a little
hacky, but I don't know of a better approach. Perhaps the ideal would
be to add a "current-selection" concept to Playgound.
That's it! Of course you also have to do the other stuff I talked about
in my previous post too. (And don't forget to turn on the #isDragSource
aspect of the Playgound instance).
Some things I don't know, but would like to:
How to do right-mouse dragging. As far as I can tell from the comments
in the image, OA themselves don't yet know how to detect right-drag from
custom views.
How to make the drag operation use an image derived from the dragged
Shape rather than the its icon. It'd be nice if there was some way to
make the Shape paint itself as required to implement this.
> Bruno Brasesco
-- chris
Locked
