Thanks for the very helpful reply. See below.
On Oct 27, 2009, at 10:22 AM, Corbin Dunn wrote:
On Oct 27, 2009, at 12:49 AM, Don Altman wrote:
Hi,
Does anyone have any insight as to how one could interrupt the auto-
expansion of an item of an NSOutlineView instance? This occurs
after a drag operation enters the item's display area without
leaving, for some predetermined time. The item's
outlineView:child:ofItem: method will then be triggered. For a
given folder, this operation might be very time-consuming,
especially if the folder has many children. I'd like to provide a
way for the user to cancel that operation (say, by moving outside
the item's display area before its children have been displayed).
It seems that the outlineView:child:ofItem: method supersedes event
handling, so it's difficult to conceive of a mechanism for the user
to communicate their intention of canceling the auto-expansion.
Please log a bug request asking for more ability to control auto
expansion.
Will do.
Ideally, your outlineView:child:ofItem: method should not take a
long time. Return something, maybe 0 children, and compute the real
children in a background thread. When it is done, reload the item.
This is how Finder and the Open and Save panel do this.
I'll use that approach. Should work.
The NSDraggingDestination protocol has a draggingEnded: method,
which the documentation says can be used to cancel auto-expansion
of a drag destination.
This may be a documentation bug. Can you point me to the location
where you read this?
file:///Developer/Documentation/DocSets/com.apple.ADC_Reference_Library.CoreReference.docset/Contents/Resources/Documents/documentation/Cocoa/Reference/ApplicationKit/Protocols/NSDraggingDestination_Protocol/Reference/Reference.html
But the method is one of those unimplemented methods, and I've
verified that it's never called. In any case, I don't understand
how the method could be called. When I log the
NSDraggingDestination method calls, they are suspended during the
outlineView:child:ofItem: execution. That would be because
everything's running in the same thread. Can anyone think of a way
to make the drag event handling and the NSOutlineView
NSOutlineViewDataSource methods run in different threads?
See my above suggestion. Ultimately, your users also have the same
problem when simply expanding the item, so it isn't an issue related
to just auto-expansion.
True, however, the overhead in auto-expansion becomes an issue when
the auto-expansion is inadvertent, when the user drags an item over a
sensitive area. If the direction of the drag is mostly horizontal, it
can linger inside a given row in the NSOutlineView for longer than
intended, triggering the auto-expand.
An alternative is to say "NO" from -shouldExpandItem: when dragging
is happening. You can determine when a drag is happening based on
the NSDraggingDestination protocol methods implemented by
NSOutlineView (subclass, and override to add your own hooks).
This would be a way to selectively disable auto-expansion, which I've
been considering. It would be nice if this were a property of the item
or of the parent NSOutlineView. Probably will make it part of the bug
report.
corbin
This seems to be an instance of a compute intensive operation
without a way of canceling it, short of doing my own mouse tracking
and forgoing the use of the NSDraggingDestination protocol and auto-
expansion in NSOutlineView.
Thanks for any insights you might provide.
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