分析时从缓存加载UITableView数据

Question

我有一个嵌套查询，如下所示，即使我使用（或我认为我使用）解析缓存，加载也需要3-4秒。它没有像我预期的那样起作用。是否有可能在第一次启动时从缓存加载，然后从解析云中更新。我是否至少需要核心数据或sqlite3来与本地端的解析同步？

另外，当我使用"query.cachePolicy"表视图得到重复的结果时，我该如何正确使用它。

- (void) retrieveSnapsFromParse {
NSString *currentUserName = [PFUser currentUser].username;
PFQuery *retrieveSnaps = [PFQuery queryWithClassName:@"Snap"];
[retrieveSnaps whereKey:@"from" equalTo:[PFUser currentUser].username];
PFQuery *retrieveSnaps2 = [PFQuery queryWithClassName:@"Snap"];
[retrieveSnaps2 whereKey:@"to" equalTo:[PFUser currentUser].username];
PFQuery * query = [PFQuery orQueryWithSubqueries:@[retrieveSnaps, retrieveSnaps2]];
query.cachePolicy = kPFCachePolicyCacheThenNetwork;
[query orderByDescending:@"createdAt"];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
    if (!error) {
    for (PFObject *object in objects) {
            Snap *snap = [Snap new];
     if([currentUserName isEqualToString:[object objectForKey:@"to"]]) {
                snap.userName = [object objectForKey:@"from"];
                snap.sentOrReceived = @"Received";
                PFFile *snapImageFile = [object objectForKey:@"snappedimage"];
                [snapImageFile getDataInBackgroundWithBlock:^(NSData *data, NSError *error) {
                    if (!error) {
                        UIImage *snapImage = [UIImage imageWithData:data];
                        snap.snapImage = snapImage;
                    }
                }];
            } else if([currentUserName isEqualToString:[object objectForKey:@"from"]]) {
                snap.userName = [object objectForKey:@"to"];
                snap.sentOrReceived = @"Sent";
            }

            snap.opened = [object[@"opened"]boolValue];
            snap.counter = [object[@"second"]intValue];
            snap.objectId = [NSString stringWithFormat:@"%@",object.objectId];
            NSDate *createdAt = object.createdAt;
            snap.createdDate = createdAt;
    // Profile image for UICustomTableViewCell
      PFQuery *userQuery = [PFUser query];
            [userQuery whereKey:@"username" equalTo:snap.userName];
             userQuery.cachePolicy = kPFCachePolicyCacheElseNetwork;
            [userQuery getFirstObjectInBackgroundWithBlock:^(PFObject *object, NSError *error) {
                if (object) {
                    snap.userFirstName = [object objectForKey:@"firstname"];
                    PFFile *imageFile = [object objectForKey:@"profileimage"];
                    [imageFile getDataInBackgroundWithBlock:^(NSData *data, NSError *error) {
                        if (!error) {
                            UIImage *image = [UIImage imageWithData:data];
                            snap.userProfileImage = image;
                        }
                    }];
                    [snapsTemp addObject:snap];
                }
        snapsTable = snapsTemp;
                    [self.tableView reloadData];
            }];
     }
    }
}];

}

下面是我在cellForRowAtIndexPath上使用的代码；

cell.cellUserProfileImage.image = snap.userProfileImage;

也在可变数组的.m文件上

    @implementation SnapsVC
{
    NSMutableArray *snapsTable;
}

Answer 1

在我将以下代码放入cellForRowAtIndexPath而不是retrieveSnapsFromParse 后，它开始按预期工作

PFQuery *userQuery = [PFUser query];
[userQuery whereKey:@"username" equalTo:snap.userName];
userQuery.cachePolicy = kPFCachePolicyCacheElseNetwork;
[userQuery getFirstObjectInBackgroundWithBlock:^(PFObject *object, NSError *error) {
    if (object) {
        PFFile *imageFile = [object objectForKey:@"profileimage"];
        [imageFile getDataInBackgroundWithBlock:^(NSData *data, NSError *error) {
            if (!error) {
                cell.cellUserProfileImage.image = [UIImage imageWithData:data];
            }
        }];
        cell.cellUserFirstNameLabel.text = [object objectForKey:@"firstname"];
    }
}];