在PFQueryTableViewController中self.objects为空

Question

我正在尝试使用PFQueryTableViewController在不同的部分显示数据。 https://parse.com/questions/using-pfquerytableviewcontroller-for-uitableview-sections中建议的代码似乎有效，但我无法在self.objects上加载数据。这是我的代码：

#import "AKAdminViewStudentsViewController.h"

@interface AKAdminViewStudentsViewController ()

@property (strong, nonatomic) NSMutableDictionary *sections;
@property (strong, nonatomic) NSMutableDictionary *sectionToClassMap;

@end

@implementation AKAdminViewStudentsViewController

@synthesize sections = _sections;
@synthesize sectionToClassMap = _sectionToClassMap;

- (id)initWithCoder:(NSCoder *)aDecoder
{
    self = [super initWithCoder:aDecoder];
    if (self) {
        self.parseClassName = @"Students";
    }

    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.

    [self.tableView reloadData];

    NSLog(@"sections found: %@", self.sections); // returns null
    NSLog(@"sectionToClassMap: %@", self.sectionToClassMap); // returns null
    NSLog(@"objects in table: %@", self.objects); // this found to be empty
}

...

#pragma mark - Tableview methods

- (PFQuery *)queryForTable
{
    PFQuery *queryStudents = [PFQuery queryWithClassName:@"Students"];
    [queryStudents whereKey:@"student_admin" equalTo:[PFUser currentUser]];

    if ([self.objects count]==0) {
        queryStudents.cachePolicy = kPFCachePolicyCacheThenNetwork;
    }

    [queryStudents orderByAscending:@"class_name"];
    return queryStudents;
}

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return self.sections.allKeys.count;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    NSString *className = [self classForSection:section];
    NSArray *rowIndicesInSection = [self.sections objectForKey:className];

    return rowIndicesInSection.count;
}

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
{
    NSString *className = [self classForSection:section];

    return className;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath object:(PFObject *)object
{
    static NSString *CellIdentifier = @"Students";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

    if (cell==nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier];
    }

    // Configure cell
    cell.textLabel.text = [NSString stringWithFormat:@"%@", object[@"full_name"]];
    NSDateFormatter *formatDate = [[NSDateFormatter alloc] init];
    [formatDate setDateStyle:NSDateFormatterShortStyle];
    cell.detailTextLabel.text = [NSString stringWithFormat:@"%@", [formatDate stringFromDate:object[@"createdAt"]]];

    return cell;
}

#pragma mark - Helper methods

- (void)objectsDidLoad:(NSError *)error
{
    [super objectsDidLoad:error];

    // Clear data before loading
    [self.sections removeAllObjects];
    [self.sectionToClassMap removeAllObjects];

    NSInteger section = 0;
    NSInteger rowIndex = 0;
    for (PFObject *object in self.objects) {
        NSString *className = [object objectForKey:@"class_name"];
        NSMutableArray *objectsInSection = [self.sections objectForKey:className];
        if (!objectsInSection) {
            objectsInSection = [NSMutableArray array];

            // Create new section for new class found
            [self.sectionToClassMap setObject:className forKey:[NSNumber numberWithInt:section++]];
        }

        [objectsInSection addObject:[NSNumber numberWithInt:rowIndex++]];
        [self.sections setObject:objectsInSection forKey:className];
    }
}

- (PFObject *)objectAtIndexPath:(NSIndexPath *)indexPath
{
    NSString *className = [self classForSection:indexPath.section];

    NSArray *rowIndicesInSection = [self.sections objectForKey:className];

    NSNumber *rowIndex = [rowIndicesInSection objectAtIndex:indexPath.row];

    return [self.objects objectAtIndex:[rowIndex intValue]];
}

- (NSString *)classForSection:(NSInteger)section
{
    return [self.sectionToClassMap objectForKey:[NSNumber numberWithInt:section]];
}

@end

当我查看NSLog数据时，self.objects为空。我知道这就是为什么没有显示数据的原因，并且想要一些建议来解决这个问题！感谢。