UITableView显示数据，然后立即变为空白

我使用CoreData从web服务中提取数据，然后将其放入tableview。当视图首次加载数据时，数据显示在tableview中，但在一瞬间，所有数据都消失了。这可能与delete代码有关（在上传新数据之前，我使用该代码清除CoreData实体），因为如果没有该代码，tableview就可以工作。我已经包含了所有用于设置数据、将数据加载到表视图、删除数据并重新加载数据的代码

代码可以在下面找到。。。感谢您的帮助。谢谢

- (void)viewDidLoad {

[super viewDidLoad];
[self findSelectedCategories];
[self setUpData];
}


- (void) findSelectedCategories {

NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"ExploreCat"];
selectedCategoriesFilter = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
}




- (void) deleteEntityData {

NSLog(@"Delete code being called");

NSManagedObjectContext *context = [self managedObjectContext];
NSFetchRequest *fetch = [[NSFetchRequest alloc] init];
[fetch setEntity:[NSEntityDescription entityForName:@"ExploreView" inManagedObjectContext:context]];
[fetch setIncludesPropertyValues:NO];

NSError *error = nil;
NSArray *entities = [context executeFetchRequest:fetch error:&error];
for (NSManagedObject * exploreView in entities) {
    [context deleteObject:exploreView];

    if (![context save:&error]) {
        NSLog(@"Can't Save! %@ %@", error, [error localizedDescription]);
    };

}

[self.tableView reloadData];
}


- (void) setUpData {

//Create the string with the userID for the get request here
NSLog(@"SetUpData being called");

//Initialize AFHTTPRequestOperationManager with Dribbble API base URL
_operationManager = [[AFHTTPRequestOperationManager alloc] initWithBaseURL:[NSURL URLWithString:@"http://www.karmo.com/explore/index"]];

[_operationManager GET:@"?user_id=5332bb35c9f9550b008ed49c" parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {

    //Success - Runs if connection is made and data recieved
    [self deleteEntityData];

    //Extrat parsed JSON file into objects to prepare for Core Data import -- Should verify if I can skip and go directly into Core Data
    for (int i = 0; i < [[responseObject valueForKey:@"belief"] count]; i++) {

        NSString * topicID = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"_id"];
        NSString * title = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"title"];
        NSString *body = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"body"];
        NSString * category = [[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"category"];
        NSNumber * nFor = @([[[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"nFor"] intValue]);
        NSNumber * nAgainst = @([[[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"nAgainst"] intValue]);
        NSNumber *totalVotes = @([nFor integerValue] + [nAgainst integerValue]);
        NSString * vote = [[[responseObject valueForKey:@"belief"] objectAtIndex:i] valueForKey:@"vote"];
        NSString *beliefID = [[[responseObject valueForKey:@"belief"] objectAtIndex:i] valueForKey:@"_id"];
        NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
        [dateFormat setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"];
        NSDate *createdAt = [dateFormat dateFromString:[[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"createdAt"]];
        NSDate *updatedAt = [dateFormat dateFromString:[[[[responseObject valueForKey:@"belief"] valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"updatedAt"]];


        NSManagedObjectContext *context = [self managedObjectContext];
        // Create a new managed object
        NSManagedObject *newExplore = [NSEntityDescription insertNewObjectForEntityForName:@"ExploreView"
                                                                    inManagedObjectContext:context];


        [newExplore setValue:topicID forKey:@"topicID"];
        [newExplore setValue:title forKey:@"title"];
        [newExplore setValue:body forKey:@"body"];
        [newExplore setValue:category forKey:@"category"];
        [newExplore setValue:nFor forKey:@"nFor"];
        [newExplore setValue:nAgainst forKey:@"nAgainst"];
        [newExplore setValue:vote forKey:@"vote"];
        [newExplore setValue:totalVotes forKey:@"totalVotes"];
        [newExplore setValue:beliefID forKey:@"beliefID"];
        [newExplore setValue:createdAt forKey:@"createdAt"];
        [newExplore setValue:updatedAt forKey:@"updatedAt"];


        // Save the object to persistent store
        NSError *error = nil;
        if (![context save:&error]) {
            NSLog(@"Can't Save! %@ %@", error, [error localizedDescription]);
        }
    }


    for (int i = 0; i < [[responseObject valueForKey:@"topic"] count]; i++) {

        NSString * topicID = [[[responseObject valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"_id"];
        NSString * title = [[[responseObject valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"title"];
        NSString *body = [[[responseObject valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"body"];
        NSString * category = [[[responseObject valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"category"];
        NSNumber * nAgainst = @([[[[responseObject  valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"nAgainst"] intValue]);
        NSNumber * nFor = @([[[[responseObject valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"nFor"] intValue]);
        NSNumber *totalVotes = @([nFor integerValue] + [nAgainst integerValue]);
        NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
        [dateFormat setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"];
        NSDate *createdAt = [dateFormat dateFromString:[[[responseObject  valueForKey:@"topic"] objectAtIndex:i] valueForKey:@"createdAt"]];

        NSManagedObjectContext *context = [self managedObjectContext];
        // Create a new managed object
        NSManagedObject *newExplore = [NSEntityDescription insertNewObjectForEntityForName:@"ExploreView"
                                                                    inManagedObjectContext:context];


        [newExplore setValue:topicID forKey:@"topicID"];
        [newExplore setValue:title forKey:@"title"];
        [newExplore setValue:body forKey:@"body"];
        [newExplore setValue:category forKey:@"category"];
        [newExplore setValue:nFor forKey:@"nFor"];
        [newExplore setValue:nAgainst forKey:@"nAgainst"];
        [newExplore setValue:totalVotes forKey:@"totalVotes"];
        [newExplore setValue:createdAt forKey:@"createdAt"];

        NSError *error = nil;
        // Save the object to persistent store
        if (![context save:&error]) {
            NSLog(@"Can't Save! %@ %@", error, [error localizedDescription]);
        }
    }



} failure:^(AFHTTPRequestOperation *operation, NSError *error) {

    //Failure

    NSLog(@"Failed to fetch shots from Karmo API!");
    UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"Unable to Connect"
                                                   message:@"We were not able to connect to the karmo database. Some data may be out of date."
                                                  delegate:self
                                         cancelButtonTitle:@"Ok"
                                         otherButtonTitles: nil];
    [alert show];

} ];


[self fetchData];}



- (void) fetchData {

NSLog(@"FetchData being called");

[exploreSortData removeAllObjects];
[exploreTableData removeAllObjects];
self.timeSortButton.backgroundColor = [UIColor clearColor];
self.voteSortButton.backgroundColor = [UIColor lightGrayColor];
NSMutableArray *subPredicates = [[NSMutableArray alloc] init];

// Fetch the recipes from persistent data store
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"ExploreView"];
exploreSortData = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];

//Would probably need to call the category slelctions here. Use an if statment to capture so if non are seletced that all the categories are displayed

if ([selectedCategoriesFilter count] > 0 ) {

    for (int i = 0; i < [selectedCategoriesFilter count]; i++) {
        NSPredicate *newPredicate = [NSPredicate predicateWithFormat:@"category ==[c] %@",[[selectedCategoriesFilter objectAtIndex:i]valueForKey:@"categorySelected"]];
        [subPredicates addObject:newPredicate];

    }


    NSPredicate *combinedPredicate = [NSCompoundPredicate orPredicateWithSubpredicates:subPredicates];

    NSArray *filterData = [[NSArray alloc]init];
    filterData = [exploreSortData filteredArrayUsingPredicate:combinedPredicate];

    NSSortDescriptor *voteDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"totalVotes" ascending:NO];

    NSMutableArray * descriptors = [[NSArray arrayWithObjects:voteDescriptor, nil]mutableCopy];
    exploreTableData  = [[filterData sortedArrayUsingDescriptors:descriptors]mutableCopy];
    [self.tableView reloadData];


} else {

    NSSortDescriptor *voteDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"totalVotes" ascending:NO];

    NSMutableArray * descriptors = [[NSArray arrayWithObjects:voteDescriptor, nil]mutableCopy];
    exploreTableData  = [[exploreSortData sortedArrayUsingDescriptors:descriptors]mutableCopy];
    [self.tableView reloadData];


}}



- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

if ([[[exploreTableData objectAtIndex:indexPath.row] valueForKey:@"beliefID"] isEqualToString:@"0"]) {

    ExploreVoteCell *cell = (ExploreVoteCell *) [tableView dequeueReusableCellWithIdentifier:@"ExploreVote" forIndexPath:indexPath];


     NSDate * topicDate = [[exploreTableData objectAtIndex:indexPath.row] valueForKey:@"createdAt"];
     NSString *currentDateString;
     NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
     [dateFormat setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"];
     currentDateString = [dateFormat stringFromDate:[NSDate date]];
     NSDate *currentDate = [dateFormat dateFromString:currentDateString];
     NSCalendar *gregorianCalendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
     NSDateComponents *dayComponents = [gregorianCalendar components:NSDayCalendarUnit
     fromDate:topicDate
     toDate:currentDate
     options:0];
     NSString *dayDifference = [NSString stringWithFormat:@"%@d", [@([dayComponents day]) stringValue]];
     NSString *voteCount = [[[exploreTableData objectAtIndex:indexPath.row] valueForKey: @"totalVotes"]stringValue];


    [cell.topicTitle setText:[[exploreTableData objectAtIndex:indexPath.row] valueForKey:@"title"]];
    [cell.votesCount setText:voteCount];
    [cell.timeDayCount setText:dayDifference];

    return cell;

} else {

    ExploreBeliefCell *cell = (ExploreBeliefCell *) [tableView dequeueReusableCellWithIdentifier:@"ExploreBelief" forIndexPath:indexPath];

    UISwipeGestureRecognizer *gesture = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(swipeRightChangeVote:)];
    gesture.direction = UISwipeGestureRecognizerDirectionRight;
    [cell addGestureRecognizer:gesture];

    [cell.topicTitle setText:[[exploreTableData objectAtIndex:indexPath.row] valueForKey:@"title"]];

    return cell;

}}

-（void）viewDidLoad{
[超级视图下载]；
[自选类别]；
[自我设置数据]；
}
-（无效）已查找的选定类别{
NSManagedObjectContext*managedObjectContext=[self-managedObjectContext]；
NSFetchRequest*fetchRequest=[[NSFetchRequest alloc]initWithEntityName:@“ExploreCat”]；
selectedCategoriesFilter=[[managedObjectContext executeFetchRequest:fetchRequest错误：nil]mutableCopy]；
}
-（void）deleteEntityData{
NSLog（@“删除正在调用的代码”）；
NSManagedObjectContext*上下文=[self-managedObjectContext]；
NSFetchRequest*fetch=[[NSFetchRequest alloc]init]；
[fetch setEntity:[NSEntityDescription entityForName:@“ExploreView”inManagedObjectContext:context]]；
[获取集合IncludePropertyValue:否]；
n错误*错误=nil；
NSArray*entities=[context executeFetchRequest:获取错误：&error]；
对于（NSManagedObject*实体中的exploreView）{
[上下文删除对象：exploreView]；
如果（！[上下文保存：&错误]）{
NSLog（@“无法保存！%@%@），错误，[错误本地化描述]；
};
}
[self.tableView重载数据]；
}
-（无效）设置数据{
//在此处为get请求创建带有用户ID的字符串
NSLog（@“正在调用的设置数据”）；
//使用Dribble API基本URL初始化AFHTTPRequestOperationManager
_operationManager=[[AFHTTPRequestOperationManager alloc]initWithBaseURL:[NSURL URLWithString:@]http://www.karmo.com/explore/index"]];
[\u operationManager GET:@”？用户id=5332bb35c9f9550b008ed49c“参数：无成功：^（AFHTTPRequestOperation*操作，id响应对象）{
//成功-如果建立连接并接收数据，则运行
[自删除实体数据]；
//Extrat将JSON文件解析为对象以准备核心数据导入——应该验证我是否可以跳过并直接进入核心数据
对于（int i=0；i<[responseObject valueForKey:@“信念”]计数]；i++）{
NSString*topicID=[[[responseObject valueForKey:@“信念”]valueForKey:@“主题”]objectAtIndex:i]valueForKey:@“您的id”]；
NSString*title=[[[[responseObject valueForKey:@“信念”]valueForKey:@“主题”]objectAtIndex:i]valueForKey:@“标题”]；
NSString*body=[[[[responseObject valueForKey:@“信念”]valueForKey:@“主题”]objectAtIndex:i]valueForKey:@“主体”]；
NSString*category=[[[responseObject valueForKey:@“信念”]valueForKey:@“主题”]objectAtIndex:i]valueForKey:@“类别”]；
NSNumber*NnE=@（[responseObject valueForKey:@“信念”]valueForKey:@“主题”]objectAtIndex:i]valueForKey:@“nE”]intValue]）；
NSNumber*nAgainst=@（[responseObject valueForKey:@“信念”]valueForKey:@“主题”]objectAtIndex:i]valueForKey:@“nAgainst”]intValue]）；
NSNumber*TotalVoces=@（[nN整型值]+[nAgainst整型值]）；
NSString*vote=[[responseObject valueForKey:@“信念”]objectAtIndex:i]valueForKey:@“投票”]；
NSString*beliefID=[[responseObject valueForKey:@“信念”]objectAtIndex:i]valueForKey:@“\u id”]；
NSDateFormatter*dateFormat=[[NSDateFormatter alloc]init]；
[dateFormat setDateFormat:@“yyyy-MM-dd'T'HH:MM:ss.SSS'Z'”；
NSDate*createdAt=[dateFormat dateFromString:[[[[responseObject valueForKey:@“信念”]valueForKey:@“主题”]objectAtIndex:i]valueForKey:@“createdAt”]；
NSDate*updatedAt=[dateFormat dateFromString:[[[[responseObject valueForKey:@“信念”]valueForKey:@“主题”]objectAtIndex:i]valueForKey:@“updatedAt”]；
NSManagedObjectContext*上下文=[self-managedObjectContext]；
//创建新的托管对象
NSManagedObject*newExplore=[NSEntityDescription insertNewObjectForEntityForName:@“ExploreView”
inManagedObjectContext:context]；
[newExplore setValue:topicID forKey:@“topicID”]；
[newExplore setValue:title forKey:@“title”]；
[newExplore setValue:body forKey:@“body”]；
[newExplore setValue:category forKey:@“category”]；
[newExplore setValue:nForkey:@“nForkey”]；
[newExplore setValue:nAgainst forKey:@“nAgainst”]；
[newExplore setValue:vote forKey:@“vote”]；
[newExplore setValue:TotalVoces-forKey:@“TotalVoces”]；
[newExplore setValue:beliefID forKey:@“beliefID”]；
[newExplore setValue:createdAt forKey:@“createdAt”]；
[newExplore setValue:updatedAt forKey:@“updatedAt”]；
//将对象保存到持久存储
n错误*错误=nil；
如果（！[上下文保存：&错误]）{
NSLog（@“无法保存！%@%@），错误，[错误本地化描述]；
}
}
对于（int i=0；i<[responseObject valueForKey:@“topic”]计数]；i++）{
NSString*topicID=[[responseObject valueForKey:@“topic”]objectAtIndex:i]valueForKey:@“U id”]；
NSString*title=[[responseObject valueForKey:@“topic”]objectAtIndex:i]valueForKey:@“title”]；
NSString*body=[[responseObject valueForKey:@“topic”]objectAtIndex:i]valueForKey:@“body”]；
NSString*category=[[responseObject valueForKey:@“topic”]objectAtIndex:i]valueForKey:@“category”]；
NSNumber*nAgainst=@（[[[responseObject valueForKey:@“topic”]objectAtIndex:i]valueForKey:@“nAgainst”]intValue]）；
NSNumber*NnE=@（[[[responseObject valueForKey:@“topic”]objectAtIndex:i]valueForKey:@“NnE”]intValue]）；
NSNumber*TotalVoces=@（[NnIntegerValue]+[nAgainst integerVa
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(modalDidChange:) name:NSManagedObjectContextObjectsDidChangeNotification object:yourManagedObjectContext];

- (void)modalDidChange:(NSNotification *)note
{
    NSSet *updatedObjects = [[note userInfo] objectForKey:NSUpdatedObjectsKey];
    NSSet *deletedObjects = [[note userInfo] objectForKey:NSDeletedObjectsKey];
    NSSet *insertedObjects = [[note userInfo] objectForKey:NSInsertedObjectsKey];

}