Re: -outlineView:heightOfRowByItem: gets an item of NULL??
Re: -outlineView:heightOfRowByItem: gets an item of NULL??
- Subject: Re: -outlineView:heightOfRowByItem: gets an item of NULL??
- From: Corbin Dunn <email@hidden>
- Date: Fri, 22 Feb 2008 12:39:56 -0800
Yes to everything, thanks!
corbin
On Feb 22, 2008, at 12:15 PM, John Stiles wrote:
OK, that makes sense. My -outlineView:numberOfChildrenOfItem:
doesn't do anything major, just returns the count of an array. I
don't foresee any problems there.
Should I file a doc enhancement bug on this, so this can get in the
docs? The -outlineView:numberOfChildrenOfItem: docs should really
have a warning here, and if there are any other cases, they should
be documented too.
If you can think of any other cases where it would be bad for -
reloadData to get called in a delegate, let me know. I would like to
see it.
Also, would you like a call stack of my NULL-item bug? Would that
help for diagnosing it?
Corbin Dunn wrote:
On Feb 22, 2008, at 11:53 AM, John Stiles wrote:
Is it illegal to call -reloadData from inside a delegate method?
It depends where. If you call -reloadData when -
numberOfChildrenOfItem: is called, then it will mess things up
(basically, that is true for any of the required methods).
Basically, you can imagine why:
for (int i = 0; i < child count; i++) {
(call delegate)
//if it reloaded, then child count may have changed...that can
cause trouble.
}
For the non-required ones, it is less essential. For acceptDrop, it
should be okay, but note that the NSOutlineView doesn't retain the
items, so you'll have to keep that in consideration. Selection
change is also okay. Sorry for the confusion -- I should have been
more specific. Your cases sound okay.
corbin
Because, yeah, when -outlineView:acceptDrop:item:childIndex: is
called, that could easily lead to the whole contents of the
outline view getting rebuilt from scratch. And this could
definitely lead to calls to -reloadData or -
reloadItem:reloadChildren:.
If this is going to bite me down the line, what are my options?
Sadly, it's not possible to defer method calls until after -
outlineView:acceptDrop:item:childIndex: returns, due to an AppKit
bug:
rdar://5686701 Drag-and-drop from an outline view runs a run-
loop in NSDefaultRunLoopMode
So I don't really know how to work around this bug without going
to extreme lengths.
Please go into a little more detail about what a delegate method
can or cannot do. Right now it's entirely possible, in some corner
cases, that small things like selection-change events (e.g. -
outlineViewSelectionDidChange:) could lead to huge ripple effects
which end up causing the whole window to rebuild itself from
scratch. If that's not kosher, I need to seriously reevaluate a
lot of code.
Corbin Dunn wrote:
> It shouldn't ask you for the height of a NULL item.
>
> This is either:
> 1. a bug in nsoutlineview
> 2. your code may be reloading the nsoutlineview in one of the
delegate methods, putting it into a "strange" state. If you see
this happening consistently, you may want to break on
NSOutlineView reloadData and see if it is getting called when it
shouldn't be.
>
> corbin
>
> On Feb 21, 2008, at 12:06 PM, John Stiles wrote:
>
>> Fair enough, but the root item is never represented graphically
in a table, so there wouldn't be a need to ask for its row height…?
>> Anyway, I filed a radar… we'll see what happens.
>>
>>
>> Mike Abdullah wrote:
>>> Although the docs don't mention it for this method, quite
often an item of nil is used to represent the tree's root object.
I would suggest therefore returning the default height of a table
cell.
>>>
>>> Mike.
>>>
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