Question

I can create an NSPredicate easily using an NSPredicateEditor (a subclass of NSRuleEditor). What I’d like to know is this:

How can I take an existing NSPredicate (one created by the editor) and reload it into the editor so that I can alter it?

EDIT: I tried @John’s suggestion of using setObjectValue:, but that didn’t quite work. Let me explain my set up a bit more:

I’ve got a Document-based cocoa app, and the Document window just has an NSPredicateEditor on it. In the dataOfType:error: method, I have:

NSPredicate * pred = [predicateEditor objectValue];
NSData * predicateData = [NSKeyedArchiver archivedDataWithRootObject:pred];
return predicateData;

In the readFromData:ofType:error: method, I have:

NSPredicate * pred = [NSKeyedUnarchiver unarchiveObjectWithData:data];
[predicateEditor setObjectValue:pred];
return (pred != nil);

I’ve verified that the predicate is getting correctly archived and unarchived, but after opening a saved predicate, the predicate is not loaded into the predicateEditor. (Yes, predicateEditor is hooked up as an IBOutlet)

Answer 1

Set the objectValue property of the NSPredicateEditor to the predicate in question.

The documentation has this description of the loading process; does any of this seem like it might cause a problem with your setup?

First, an instance of
NSPredicateEditor is created, and some
row templates are set on it—either
through a nib file or
programmatically. The first thing
predicate editor does is ask each of
the templates for their views, using
templateViews.

After setting up the predicate editor,
you typically send it a
setObjectValue: message to restore a
saved predicate. NSPredicateEditor
needs to determine which of its
templates should display each
predicate in the predicate tree. It
does this by sending each of its row
templates a matchForPredicate: message
and choosing the one that returns the
highest value.

After finding the best match for a
predicate, NSPredicateEditor copies
that template to get fresh views,
inserts them into the proper row, and
then sets the predicate on the
template using setPredicate:. Within
that method, the
NSPredicateEditorRowTemplate object
must set its views’ values to
represent that predicate.

NSPredicateEditorRowTemplate next asks
the template for the “displayable
sub-predicates” of the predicate by
sending a
displayableSubpredicatesOfPredicate:
message. If a template represents a
predicate in its entirety, or if the
predicate has no subpredicates, it can
return nil for this. Otherwise, it
should return a list of predicates to
be made into sub-rows of that
template’s row. The whole process
repeats for each sub-predicate.