未保存Ios核心数据

我使用的是核心数据，我遇到了一个问题。当我保存数据且应用程序仍在运行时，我可以查看并获取已保存的数据

一旦应用程序关闭，所有字段都将删除，只保存对象。我可以在saveContext方法中看到这一点。 第一次启动时，当应用程序关闭时，saveContext方法被激活。我可以看到managedObjectContext对象正在插入新对象。 下次打开应用程序时，managedObjectContext会更新对象，以便我知道它会保存对象，但当我尝试检索对象时，它会找到

以下是插入对象的方式：

AppDelegate* appDelegate = [UIApplication sharedApplication].delegate;

    self.managedObjectContext = appDelegate.managedObjectContext;

    @try {
        UserData *userData  =[NSEntityDescription insertNewObjectForEntityForName:[UserTable tableName]                                               inManagedObjectContext:self.managedObjectContext];

        //Insert Values
        userData.facebookId=user.id;
        userData.name=user.name;
        userData.picoAccessToken=[PicoApiManager sharedInstance].accessToken;
        userData.picoExpire=[PicoApiManager sharedInstance].expires;
        userData.latitude=[NSNumber numberWithDouble:user.latitude];
        userData.longitude=[NSNumber numberWithDouble:user.longitude];
        userData.pushId=user.pushId;
        userData.isActive=[NSNumber numberWithBool:activeStatus];
    }
    @catch (NSException *exception) {
        NSLog(@"Insert exception - %@", exception.description);
    }

或

这是应用程序代理功能：

     - (void)saveContext
{
    NSError *error = nil;
    NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
    if (managedObjectContext != nil) {
        if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
             // Replace this implementation with code to handle the error appropriately.
             // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. 
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        } 
    }
}

#pragma mark - Core Data stack

// Returns the managed object context for the application.
// If the context doesn't already exist, it is created and bound to the persistent store coordinator for the application.
- (NSManagedObjectContext *)managedObjectContext
{
    if (_managedObjectContext != nil) {
        return _managedObjectContext;
    }

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil) {
        _managedObjectContext = [[NSManagedObjectContext alloc] init];
        [_managedObjectContext setPersistentStoreCoordinator:coordinator];
    }
    return _managedObjectContext;
}

// Returns the managed object model for the application.
// If the model doesn't already exist, it is created from the application's model.
- (NSManagedObjectModel *)managedObjectModel
{
    if (_managedObjectModel != nil) {
        return _managedObjectModel;
    }
    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Pico-Db" withExtension:@"momd"];
    _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
    return _managedObjectModel;
}

// Returns the persistent store coordinator for the application.
// If the coordinator doesn't already exist, it is created and the application's store added to it.
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
    if (_persistentStoreCoordinator != nil) {
        return _persistentStoreCoordinator;
    }

    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Pico.sqlite"];

    NSError *error = nil;
    _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }    

    return _persistentStoreCoordinator;
}

// Returns the URL to the application's Documents directory.
- (NSURL *)applicationDocumentsDirectory
{
    return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}

这就是我试图获取数据的方式：

  AppDelegate* appDelegate = [UIApplication sharedApplication].delegate;
    //2
    // initializing NSFetchRequest
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

    //Setting Entity to be Queried
    NSEntityDescription *entity = [NSEntityDescription entityForName:[UserTable tableName] inManagedObjectContext:appDelegate.managedObjectContext];


    [fetchRequest setEntity:entity];
    NSError* error;

    // Query on managedObjectContext With Generated fetchRequest
    NSArray *fetchedRecords = [appDelegate.managedObjectContext executeFetchRequest:fetchRequest error:&error];
    if (fetchedRecords.count >0) {
        return YES;
    }

    return NO;

---

插入数据后必须调用

-[AppDelegate saveContext]

，以便CoreData将更改持久化到磁盘。

NSManagedObjectContext

将在内存中存储更改，以便在应用程序仍处于活动状态时，您可以访问数据。但是，一旦应用程序终止，除非您调用

-[AppDelegate saveContext]

，否则这些更改将不会持久化

在第一个示例中尝试以下操作：

AppDelegate *appDelegate  = [UIApplication sharedApplication].delegate;
self.managedObjectContext = appDelegate.managedObjectContext;

@try {
    UserData *userData = [NSEntityDescription insertNewObjectForEntityForName:[UserTable tableName] inManagedObjectContext:self.managedObjectContext];

    //Insert Values
    userData.facebookId=user.id;
    userData.name=user.name;
    userData.picoAccessToken=[PicoApiManager sharedInstance].accessToken;
    userData.picoExpire=[PicoApiManager sharedInstance].expires;
    userData.latitude=[NSNumber numberWithDouble:user.latitude];
    userData.longitude=[NSNumber numberWithDouble:user.longitude];
    userData.pushId=user.pushId;
    userData.isActive=[NSNumber numberWithBool:activeStatus];

} @catch (NSException *exception) {
    NSLog(@"Insert exception - %@", exception.description);
}

// SAVE CONTEXT:
[appDelegate saveContext];

在第二个示例中尝试以下操作：

for (Picture *picture in Pictures) {
    // Checks if inserted picture is already inside the table

    AppDelegate* appDelegate  = [UIApplication sharedApplication].delegate;
    self.managedObjectContext = appDelegate.managedObjectContext;

    @try {
        PictureData *pictureData = [NSEntityDescription insertNewObjectForEntityForName:[PicturesTable tableName]inManagedObjectContext:self.managedObjectContext];

        //Insert Values
        pictureData.url=picture.source;
        pictureData.isNew=[NSNumber numberWithBool:YES];
        pictureData.isPick=[NSNumber numberWithBool:NO];
        pictureData.timeTaken=picture.time_taken;
        pictureData.albumData=[self getActiveAlbum];

    } @catch (NSException *exception) {
        NSLog(@"Insert exception - %@", exception.description);
    }
}

// SAVE CONTEXT:
[appDelegate saveContext];

要创建提取请求，请执行以下操作：

NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"YourEntityName"];
request.sortDescriptors = [NSSortDescriptor sortDescriptorWithKey:@"attributeName" ascending:YES];
request.predicate       = [NSPredicate predicateWithFormat:@"attribute == %@", 13];

NSError *error   = nil; // 
NSArray *results = [appDelegate.managedObjectContext executeFetchRequest:request error:&error];
if (!results) {
    NSLog(@"Error performing fetch request: %@", error.localizedDescription);
}

return ([results count] > 0); // There are more efficient ways of getting count from CoreData

---

在应用程序终止之前，在applicationWillTerminate中，我正在调用saveContext方法。那个电流？或者我每次插入数据时都需要调用此函数？

applicationWillTerminate

不保证被调用。不应依赖它来保存您的

NSManagedObjectContext

。上下文应该在插入数据后保存，或者在应用程序中的下一个逻辑点保存。嘿，抱歉，但由于某些原因，它没有帮助。我用来获取信息的代码可以吗？请看我更新的答案。当您只需将实体名称传递给

NSFetchRequest

初始值设定项时，不确定为什么需要麻烦地创建

NSEntityDescription

。

NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"YourEntityName"];
request.sortDescriptors = [NSSortDescriptor sortDescriptorWithKey:@"attributeName" ascending:YES];
request.predicate       = [NSPredicate predicateWithFormat:@"attribute == %@", 13];

NSError *error   = nil; // 
NSArray *results = [appDelegate.managedObjectContext executeFetchRequest:request error:&error];
if (!results) {
    NSLog(@"Error performing fetch request: %@", error.localizedDescription);
}

return ([results count] > 0); // There are more efficient ways of getting count from CoreData