Iphone iOS+；Parse.com:kPFCachePolicyCacheThenNetwork，检索数据两次

我已经使用Parse.com

我想先从缓存检索数据&然后从网络

为此，我使用了kPFCachePolicyCacheThenNetwork缓存策略，这是我所需要的

PFQuery *employesquery = [PFQuery queryWithClassName:@"employesTable"];
    [employesquery whereKey:@"UserID" equalTo:[PFUser currentUser]];
    [employesquery includeKey:@"empID"];
    [employesquery includeKey:@"empID.user"];

    MBProgressHUD *hud = [MBProgressHUD showHUDAddedTo:self.navigationController.view  animated:YES];


//APPLIES CACHE... ********
        employesquery.cachePolicy = kPFCachePolicyCacheThenNetwork;

    [employesquery findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
        [hud hide:YES];
        NSMutableArray *empData = [[NSMutableArray alloc] init];
        for (PFObject *object in objects)
        {
            //Getting Data For Item
            PFObject *employeeObject = [object objectForKey:@"empID"];
            [empData addObject:employeeObject];
        }
        [self fetchEmployeeData:empData];

    }];

但使用此方法，每个数据检索两次可重复的数据

如何避免此重复数据，

一旦数据从网络中获取，先前显示的数据（使用缓存）将被清除/隐藏

我尝试了

[PFQuery clearlallcachedresults]

已清除所有缓存，以便下次迭代时缓存中没有数据。
使用
kPFCachePolicyCacheThenNetwork
作为缓存策略时，您的回调始终会触发两次。这是因为策略是使用缓存，然后转到网络，而不是专门使用缓存

解决方案是跟踪块被调用的次数，以便确定是从网络获取缓存结果还是新结果。Parse have.
必须清除数据数组，该数组用于在块findobjectsinbackgroundithblock:^（NSArray*objects，NSError*error）中从Parse查询存储对象

-（无效）刷新数据
{
PFUser*currentUser=[PFUser currentUser]；
NSPredicate*谓词=[NSPredicate谓词WithFormat:[NSString stringWithFormat:@“%@=”%@“或%@=”%@“，
kMessageUserSendIdKey，currentUser.objectId，
kMessageUserReceiveIdKey，currentUser.objectId]]；
PFQuery*query=[PFQuery queryWithClassName:kMessageClassKey谓词：谓词]；
[查询添加下降顺序：kMessageTimeCreatedKey]；
[查询includeKey:kMessageUserSendKey]；
[查询includeKey:kMessageUserReceiveKey]；
[查询setCachePolicy:kPFCachePolicyCacheThenNetwork]；
[查询findObjectsInBackgroundWithBlock:^（NSArray*对象，NSError*错误）{
如果（！错误）{
//TODO:清除数据数组
self.messagesDataArray=[NSMutableArray new]；
如果（objects.count>0）{
[self.messagesDataArray addObject:objects[0]]；
for（int i=1；i

- (void)refreshData
{
    PFUser *currentUser = [PFUser currentUser];

    NSPredicate *predicate = [NSPredicate predicateWithFormat:[NSString stringWithFormat:@"%@ = '%@' OR %@ = '%@'",
                                                           kMessageUserSendIdKey, currentUser.objectId,
                                                           kMessageUserReceiveIdKey, currentUser.objectId]];

PFQuery *query = [PFQuery queryWithClassName:kMessageClassKey predicate:predicate];
[query addDescendingOrder:kMessageTimeCreatedKey];
[query includeKey:kMessageUserSendKey];
[query includeKey:kMessageUserReceiveKey];
[query setCachePolicy:kPFCachePolicyCacheThenNetwork];

[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
    if (!error) {
        // TODO: Clear the data array
        self.messagesDataArray = [NSMutableArray new];

        if (objects.count > 0) {
            [self.messagesDataArray addObject:objects[0]];
            for (int i = 1; i < objects.count; i++) {
                PFObject *messageChat = [objects objectAtIndex:i];
                if (![self isExistWithMessageChat:messageChat]){
                    [self.messagesDataArray addObject:messageChat];
                }
            }
            [self.tableView reloadData];
        }
     }
     else {
        NSLog(@"Error: %@ %@", error, [error userInfo]);
     }
   }];
}