NSArrayController without loading a large data array into an array

Question

I would like to use NSArrayController to provide data in an NSTableView. The problem I am facing is that I do not want to preload all my data into an array, and then use the array controller methods setContent: My data model is a large existing code base that manages millions of records. It contains methods for efficiently returning a set of data rows.

Following the example that I found while limiting the number of objects in NSArrayController, I tried to subclass NSArrayController and override the arrangedObjects: method to return the proxy class of the array I wrote. The array proxy class provides the count: and objectAtIndex: methods. The object returned by objectAtIndex: is an NSDictionary. When I tried to return my proxy from the arrangedObjects: method, called both count: and objectAtIndex: but I also get an unrecognized selection error in my proxy class for the array for _valueForKeyPath:ofObjectAtIndex: It looked like a private method, so I did not continue to go that route.

I also thought about returning a smaller array of data from arrangedObjects: but could not figure out how I would determine which rows NSTableView was trying to display.

Is the data source the “right” way to interact with my existing data model, or is there some way to get NSArrayController working?

Answer 1

NSArrayController is already working, with proxies and indexes and lazy loading and all shabang. Have you tried using it as is? If after that you feel the need for microcontrol of data loading, use NSFetchRequest. Subclass NSArrayController and add an initializer along these lines:

 + (id)arrayControllerWithEntityName: (NSString *)entityName error:(NSError **)error { id newInstance = [[[self alloc] initWithContent:nil] autorelease]; [newInstance setManagedObjectContext:[[NSApp delegate] managedObjectContext]]; [newInstance setEntityName:entityName]; [newInstance setAutomaticallyPreparesContent:YES]; [newInstance setSelectsInsertedObjects:YES]; [newInstance setAvoidsEmptySelection:YES]; [newInstance setAlwaysUsesMultipleValuesMarker:YES]; NSFetchRequest *dontGobbleRequest = [[[NSFetchRequest alloc] init] autorelease]; //configure the request with fetchLimit and fetchOffset an' all that NSError *err; if ([newInstance fetchWithRequest:dontGobbleRequest merge:YES error:&err] == NO) { //better check docs whether merge:YES is what you want if(*error && err) { *error = err; } return nil; } return newInstance; } 

You will need to do some research on the various features and configurations, but you will get an image.