How do you live-filter an NSArray or NSMutableArray?

Question

I'd like to have an NSArray or NSMutableArray that always shows a filtered view of a data set. That is, if the filter is set to "show me things with the letter a", and an item "blah" is added, that item would automatically show up in the list. However, if "bluh" were added, it would not show up in the filtered list (but would still really be there in the underlying dataset).

I see that there are filter methods on NSArray and NSMutableArray, but these are one shot methods. That is, the filter occurs when you call the method and never again (unless of course you call the filter method again).

I'm coming from the Java world, were I used Glazed Lists extensively for this kind of thing. I was hoping for a similar solution baked into Cocoa.

Answer 1

Coming from the iPhone, I'm not very familiar with NSArrayController but you might want to take a look at it. It seems to me that setFilterPredicate: in combination with setAutomaticallyRearrangesObjects:YES might do the trick.

Other than that, it should be quite easy to roll your own solution using Key-Value Observing. Start with a mutable copy of the array you want to filter and filter it with filterUsingPredicate: as you noted above, then register yourself as an observer for insertions and deletions in the original array and when your observer method gets called, call evaluateWithObject: on the newly inserted objects to decide whether to insert them into your filtered array.