ios - NSSortDescriptor 排序正值

Question

在我的核心数据中，我要求 x 个按距离 (NSNumber[double]) 升序排序的对象。问题是它还给我返回负数。我知道这是有道理的，但我只想要正数，我该怎么做？

NSManagedObjectContext *context = generateManagedObjectContext();

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:kCORE_DATA_ALL_TRAPS_ENTITY inManagedObjectContext:context];
    [fetchRequest setEntity:entity];

    // Specify how the fetched objects should be sorted
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:DISTANCE_TO_CLOSE_POINT ascending:YES];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObjects:sortDescriptor, nil]];

    // Limit the restlus to specific number
    [fetchRequest setFetchLimit:numberOfTraps];

    NSError *error = nil;
    NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
    if (fetchedObjects == nil || fetchedObjects.count == 0) {
        NSLog(@"%s error: %@", __PRETTY_FUNCTION__, error.localizedDescription);
        return nil;
    }

Answer 1

试试这个，

 NSPredicate *predicate = [NSPredicate predicateWithFormat:@"distance >= %d", 0];

[fetchRequest setPredicate:predicate];