NSFetchedResultsController titleForHeaderInSection with formatted NSDate

问题

In my Core Data app I am using a FetchedResultsController. Usually to set titles for headers in a UITableView you would implement the following method like so:

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section { 
    id <NSFetchedResultsSectionInfo> sectionInfo = [[<#Fetched results controller#> sections] objectAtIndex:section];
    return [sectionInfo name];
}

where [sectionInfo name] returns a NSString.

my sectionKeyPath is based on an NSDate and this all works fine apart from the section headers it gives me are the raw date description strings (e.g. 12/12/2009 12:32:32 +0100) which look a bit of a mess in a header!

So I want to use a date formatter on this to make a nice header like "Apr 17 2010" but I can't do that with the [sectionInfo name] as this is NSString! Any Ideas?

Many Thanks

回答1:

I found a solution:

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
    //Returns the title for each section header. Title is the Date.
    id <NSFetchedResultsSectionInfo> sectionInfo = [[fetchedResultsController sections] objectAtIndex:section];
    NSArray *objects = [sectionInfo objects];
    NSManagedObject *managedObject = [objects objectAtIndex:0];
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateStyle:NSDateFormatterMediumStyle];
    NSDate *headerDate = (NSDate *)[managedObject valueForKey:@"itemDate"];
    NSString *headerTitle = [formatter stringFromDate:headerDate];
    [formatter release];
    return headerTitle;
}

Please look over this, if you know of a better way please say!

Otherwise if your stuck with a similar problem I hope this helps!

回答2:

In iOS 4.0 and later, use the [NSDateFormatter localizedStringFromDate] class method and you won't have to worry about managing the NSDateFormatter instance. Otherwise this seems to be the only way to do it.

回答3:

This is the Swift version of the answer:

override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {        
    let sectionInfo = fetchedResultsController.sections![section]
    let objects = sectionInfo.objects
    if let topRecord:NSManagedObject = objects![0] as? NSManagedObject  {
        let formatter = DateFormatter()
        formatter.dateStyle = .medium
        return formatter.string(from: topRecord.value(forKey: "itemDate") as! Date)
    } else {
        return sectionInfo.indexTitle
    }
}

来源：https://stackoverflow.com/questions/2660105/nsfetchedresultscontroller-titleforheaderinsection-with-formatted-nsdate