As a follow-up question to a previous post: filtering content for UITableView
When filtering a data set for UITableViews, assuming I used NSPredicate per the recommendation in the previous post, does the general idea look like this:
NSArray *allData;
NSMutableArray *filteredData;
- When the filter button is pressed, use NSPredicate to populate
- filteredData Reload the table with
[tableView reloadData];
In my tableView datasource and delegate methods, I’d basically check if the filter button was on, and if it was show the filteredData, if not, show allData.
The thing I am unsure about, in one of the WWDC 2010 videos about tableviews, they say that reloadData is an expensive operation, and you should be updating your view instead using insert/delete/replace methods for the tableView. And the animation also gives the user context of what is happening. So if that is the case, do you still use reloadData? I can’t seem to figure out how the tableViews would know what to show if the filter was turned on and reloadData was not called. I’m assuming that you would have to reloadData if a filter was on, and then also update the view with the insert/delete/replace methods for the animation if you wanted to give the user some context of what is happening. Is that right? Thanks.
If I understand you correctly the dataset isn’t changing just the order in which it’s being displayed,(Filtered). If this is the case calling reload data is the correct thing to do. Using the insert/remove/delete animations is primarily for editing a tableview(when in editing mode). Or when receiving “more” data or data updates(like from iCloud). I’ve only found calling reload data on a tableview to be expensive if the dataSource is extremely large with uncached images or some other large slow reading data(as in restful XML calls to remote servers). If your dealing primarily with text and/or small cached images it shouldn’t be any problem at all. If the filtering is removing or adding items to your array, you need to track where in the tableview they are , by index path , remove them, and then add the new pieces. Keeping more than one array around for a single datasource is way more expensive given the platform. Memory management is priority when we’re dealing with iOS, IMHO.
One other thing to note here is the actual insertion and/or deletion of rows or sections has to be inside of an animation block begining with [beginUpdates] and finishing with [endUpdates]. Unless your doing it from inside the editing delegate methods.