Search on Core data backed UITable issue? - search

Question

Not sure if this is the right place (I am sure someone will let me know if it is not) I have a iPhone application that has a UITableview that is backed by core data. I want to perform a reducing search so that only the items starting with the characters entered into the search bar are shown. This is normally done with the delegate - (void)searchBar:(UISearchBar *)searchBar textDidChange:(NSString *)searchText no problem. I am a little confused as I am new to Core Data how to do this. One of the big problems as I see it is going to be updating the interface to let it know what to present. I assume an alternative NSFetchedResultsController needs to be sent to the UITableView is that correct?
So here are my issues:
1) I assume I need to create a NSFetchedResultsController with only the correct items in it then tell the UITableView to use this as the dataSource and reload the table?
2) is there a better way than executing a full sorted fetch and removing those objects that do not conform. ie is there a way of doing a select where type fetch?
Thanks in advance and sorry if this is a dumb question.
Regards
Damien

Answer 1

Yes, you will need a new NSFetchedResultsController.
You should use a NSPredicate in your new NSFetchRequest to filter by your search text.
For example, if your managed objects have a field "name" that should be filtered:
NSPredicate *pred = [NSPredicate predicateWithFormat:#"%K beginswith[c] %#", #"name", searchText];
[fetchRequest setPredicate:pred];

Answer 2

I used a slightly different solution: instead of relying on a different NSFetchedResultsController, I created a NSMutableArray (filteredListContent) in my table view controller, used to store the temporary data, as inspired by Apple sample code and Mugunth Kumar's tutorial.
In tableView:cellForRowAtIndexPath:, returning the appropriate data-source array:
if(receivedTableView == self.searchDisplayController.searchResultsTableView){
Objects* object = [self.filteredListContent objectAtIndex:indexPath.row];
cell.textLabel.text = object.name;
} else {
Objects* object = [self.unfilteredListContent objectAtIndex:indexPath.row];
cell.textLabel.text = object.name;
}
As in Apple's sample code, add pretty much the same method in other methods, such as
- (NSInteger)tableView:(UITableView *)receivedTableView numberOfRowsInSection:(NSInteger)section {
if(receivedTableView == self.searchDisplayController.searchResultsTableView){
return [self.filteredListContent count];
}
return [self.unfilteredListContent count];
}
As well as in tableView:didSelectRowAtIndexPath:...
Then conformed to UISearchDisplayDelegate protocol and added the following methods:
- (void)filterContentForSearchText:(NSString*)searchText
{
if (!self.filteredListContent) {
self.filteredListContent = self.filteredListContent = [[NSMutableArray alloc] init];
}
[self.filteredListContent removeAllObjects];
for (Objects *object in [self.coreDataStuffVariable.fetchedResultsController fetchedObjects])
{
NSPredicate *predicate = [NSPredicate predicateWithFormat:
#"(SELF contains[cd] %#)", searchText];
NSString * elementTitle = [NSString stringWithFormat:#"%#", object.name];
[elementTitle compare:searchText options:NSCaseInsensitiveSearch];
if([predicate evaluateWithObject:elementTitle])
{
[self.filteredListContent addObject:password];
}
}
}
- (BOOL)searchDisplayController:(UISearchDisplayController *)controller
shouldReloadTableForSearchString:(NSString *)searchString{
[self filterContentForSearchText:searchString];
// Return YES to cause the search result table view to be reloaded.
return YES;
}
Pretty simple. I guess it can end up badly if the core data objects are reloaded during a search, but well... if you can sleep knowing that then it may be a good solution!