The only way I have done this is to build the thing in IB.
Forget the NSSearchField.
First add a Predicate Editor to a window. This gives you a top-level compound
predicate ("Any of the following are true") and a single predicate template.
The predicate template has three parts, a left expression, a set of operators,
and a right expression. Click on the template to show its attributes in the
Inspector.
Each template combines a single type of L.E, e.g. Key Paths, and a single type
of R.E., e.g. Strings, and a set of operators. For instance, all the searchable
key paths that have string values are included in a single template. You would
add "cardName" and any other searchable string variable. In the middle section,
select the required comparison operators. The R.E. is then set to Strings, and
since these are provided by the user, you don't list them here. If you had a
date variable, then you make another template, this time setting the R.E. to
Date. Obviously there are many combinations possible, since there are 6
possibilities for L.E. and R.E. You need to work out the characteristics of
each template appropriately.
You must understand that, although the editor you create in I.B. looks visually
like the filter predicate the user creates, it really is very different. The
set of the templates you create in I.B. define the types of comparisons the
user can make, but doesn't create any instances of them. The user instantiates
as many of each template as he likes at run time to build the total predicate.
When you enter the list of L.E.s, the left popup in the row template is
populated with choices that have the same names as appear in the L.E. list. You
can change the popup item strings by double-clicking the item and changing the
string, in the usual way.
Once you understand this much, you should understand how many templates you
need. (This does not mean how many filter comparisons the user can define,
which are unlimited, but how many types of comparisons your program allows. For
instance, a comparison of a key path to a string would be one, to a date would
be another, to a constant a third, and so on.) Call this number N. Now you
should examine the Editor itself in the Inspector and set the number of
templates to N. This will produce N templates. You set up each one of them to
match one of the types of comparison.
The editor also has an attribute to allow all rows to be deleted. If this is
turned on, then the top row template can be deleted by the user using the minus
button. If the user does this, then the top level compound row also disappears
(sometimes), leaving a totally blank view, which makes the editor useless. At
least this was the case under Leopard. So you pretty much have to turn this
off. This leaves you with a predicate that must have at least one comparison,
even if you might like to have a predicate editor without any comparisons,
which would match everything. I'm suspicious that I don't quite understand
what's going on here, but I haven't achieved any greater clarity.
Now, when the editor is created out of the nib file, it is created with a
single empty compound. But since this produces a editor that is totally blank,
it is useless. So at some early stage, for instance, in awakeFromNib, you have
to add a row by sending the editor an addRow message. Adding this row actually
produces two rows, since once a row template is added, the compound row also
appears, and you're good to go.
I have used the action method of the predicate editor to inform my app delegate
that the user has changed the predicate, which I then apply to an array
controller. There are probably other approaches.
I have not created one of these in Snow Leopard, so some of the details may
have changed.
Tim Larkin
Abstract Tools
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