从Firebase数据库检索数据并填充UITableViewController

Question

使用Firebase数据库中的数据填充表视图时遇到一些问题。我的NSMutableArray在块内始终为空。如何用从数据库中获取的数据填充tableView？

仅目标C

到目前为止，我已经以这种方式实现了代码

@interface UserSearchController ()
@property (nonatomic, strong) NSMutableArray *users;
@end

@implementation UserSearchController

-(void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];

    [self.tableView registerClass:[UITableViewCell class] forCellReuseIdentifier:@"cellID"];

    [self retrieveAllUser];
}

-(void)retrieveAllUser {

    FIRDatabaseReference *dbRef = FIRDatabase.database.reference;

    _users = NSMutableArray.new;

    [[[dbRef child:kUserAccFolder] queryOrderedByChild:kUserAccEmail]
     observeEventType:FIRDataEventTypeChildAdded withBlock:^(FIRDataSnapshot *snapshot) {

         [self.users addObject:snapshot.value[kUserAccName]];
         [self.tableView reloadData];
     }];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return _users.count;
}


- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"cellID" forIndexPath:indexPath];

    cell.textLabel.text = [NSString stringWithFormat:@"%@",self.users[indexPath.row]];

    return cell;
}