On Aug 12, 2009, at 3:20 PM, Dave DeLong wrote:
Thanks for the info! I spent some time at NSCoder Night last night
poking around with attempting to convert an NSPredicate into an
NSCompoundPredicate using the TODParseKit and the BNF definition of
NSPredicate grammar in the docs, then eventually gave up. =) (I
figured there had to be an easier way, since this seems like a non-
unreasonable thing to want to do)
Luckily, I was just pointed to the setObjectValue: approach on
StackOverflow.com and have been trying to get that to work.
I've started building a test app to experiment with this. Here's
what I've got:
1. Create a new Document-based Cocoa App.
2. Add an IBOutlet to MyDocument called "predicateEditor"
3. Drop an NSPredicateEditor into MyDocument.xib and connect it to
File's Owner's predicateEditor outlet.
4. Add a "[predicateEditor addRow:self];" message in MyDocument's
windowControllerDidLoadNib: method
5. In the dataOfType:... method, retrieve predicateEditor's
objectValue, use NSKeyedArchiver to archive it, and return that as
the data.
6. In the readData:ofType:... method, unarchive the data as an
NSPredicate and use predicateEditor's setObjectValue: method to
restore it.
If I run this, create a predicate, and save it, then it saves nicely
to a file. If I then try to open that file, I can NSLog and see that
the predicate is getting unarchived properly, but the
predicateEditor doesn't load it. Is there anything I'm supposed to
be doing besides setObjectValue:? I haven't modified the
predicateEditor at all, other than to make the nesting "Compound".
In document based apps, readData:ofType: is called before the nib is
loaded. So in your readData:ofType: method, the outlet to the
NSPredicateEditor has not yet been populated, so that setObjectValue:
goes to nil.
You can unarchive the predicate and store it in your MyDocument, and
then push it to the NSPredicateEditor in windowControllerDidLoadNib:.
Alternatively, if you're comfortable with bindings, you you can bind
the NSPredicateEditor's object value to your document in IB, and then
it will pick up the predicate when it's loaded.
Hope this helps,
-Peter
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