Objective c 重新启动应用程序时数据丢失（核心数据）

伙计，希望你没事

我是iPhone开发新手。我正在使用核心数据创建一个简单的应用程序。在应用程序中，当我保存数据时，它工作正常，然后我检索数据时，它也工作正常。但是当我重新启动我的应用程序时，所有的数据都丢失了

启动应用程序时，在ViewDidLoad函数中，我使用在工作应用程序期间检索的相同函数检索数据

保存数据的方法：

    NSManagedObjectContext *context=[app managedObjectContext];
    Contacts *data=[NSEntityDescription insertNewObjectForEntityForName:@"Contacts" inManagedObjectContext:context];
    if(nameField.text.length <=0 || phoneField.text.length <=0 )
    {

        UIAlertView *alert=[[UIAlertView  alloc]initWithTitle:@"Warning!" message:@"Please enter some data." delegate:self cancelButtonTitle:@"Ok" otherButtonTitles: nil];
        [alert show];
    }
    else
    {
        data.name = nameField.text;
        data.phone = phoneField.text;
        NSLog(data.name);
        NSLog(data.phone);
        [self.navigationController popToRootViewControllerAnimated:YES];

    }

    NSEntityDescription *entity=[NSEntityDescription entityForName:@"Database" inManagedObjectContext:context];

    NSFetchRequest *fetchRequest=[[NSFetchRequest alloc]init];

    [fetchRequest setFetchBatchSize:20];

    [fetchRequest setEntity:entity];

    NSSortDescriptor *sorting = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];

    NSArray *sorted_Array=[NSArray arrayWithObject:sorting];

    [fetchRequest setSortDescriptors:sorted_Array];

    NSError *error;

    NSMutableArray *tArray=[[context executeFetchRequest:fetchRequest error:&error]mutableCopy];

    [self setArray:tArray];
    [self.tableView reloadData];

应用程序代理代码

#import "ZAppDelegate.h"
#import "Contacts.h"

@implementation ZAppDelegate

@synthesize window = _window;
@synthesize managedObjectContext = __managedObjectContext;
@synthesize managedObjectModel = __managedObjectModel;
@synthesize persistentStoreCoordinator = __persistentStoreCoordinator;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.

    TableViewController *TVC=[[TableViewController alloc]init];

    TVC.MOcontext=self.managedObjectContext;

    UINavigationController *nvgc=[[UINavigationController alloc]initWithRootViewController:TVC];
    self.window.rootViewController=nvgc;


    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}

- (void)applicationWillResignActive:(UIApplication *)application
{
    /*
     Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
     Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
     */
}

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    /*
     Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later. 
     If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
     */
}

- (void)applicationWillEnterForeground:(UIApplication *)application
{
    /*
     Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.
     */
}

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    /*
     Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
     */
}

- (void)applicationWillTerminate:(UIApplication *)application
{
    // Saves changes in the application's managed object context before the application terminates.
    [self saveContext];
}

- (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]);
            abort();
        } 
    }
}

#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:@"Diary" 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:@"Diary.sqlite"];

    NSError *error = nil;
    __persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    if (![__persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&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. 

         Typical reasons for an error here include:
         * The persistent store is not accessible;
         * The schema for the persistent store is incompatible with current managed object model.
         Check the error message to determine what the actual problem was.


         If the persistent store is not accessible, there is typically something wrong with the file path. Often, a file URL is pointing into the application's resources directory instead of a writeable directory.

         If you encounter schema incompatibility errors during development, you can reduce their frequency by:
         * Simply deleting the existing store:
         [[NSFileManager defaultManager] removeItemAtURL:storeURL error:nil]

         * Performing automatic lightweight migration by passing the following dictionary as the options parameter: 
         [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

         Lightweight migration will only work for a limited set of schema changes; consult "Core Data Model Versioning and Data Migration Programming Guide" for details.

         */
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }    

    return __persistentStoreCoordinator;
}

#pragma mark - Application's Documents directory

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

@end

这里有什么问题吗？

---

我希望尽早得到好的答案。

在应用程序生命周期的某个时刻，您需要在

NSManagedObjectContext

上调用

save

，否则您所做的更改将不会持久保存到

NSPersistentStore

。例如，在应用程序委托的

applicationidenterbackground:

方法中

NSError *saveError = nil;
if( ![[self managedObjectContext] save:&saveError] ) {
   //  deal with error...
}

---

我假设您的应用程序代理像Apple模板一样设置和维护核心数据堆栈…

我看不出您在代码中的保存位置。您需要告诉managedcontext保存。你在哪里做这取决于你的应用程序和设计。如果您认为它已经存在于您的应用程序中的某个地方，请添加一些NSLog以尝试和调试，或者使用调试器工具实际进入您的代码

这很容易解决。祝你好运。

在应用程序中代表：

- (void)applicationWillTerminate:(UIApplication *)application
{
  // Saves changes in the application's managed object context before the application terminates.
  [self saveContext];
}

在早期版本的Xcode模板中，

-saveContext

可能是

-save

---

此外，您还可以在其他类中调用

-save

或

-saveContent

方法：

[(AppDelegate *)[UIApplication sharedApplication] saveContext];

---

NSManagedObjectContext提供了一个便笺簿：您可以对对象执行任何操作，但需要在最后保存它。在保存NSManagedObjectContext之前，对其所做的任何更改都是临时的。尝试将以下内容添加到方法末尾：

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

---

需要保存此上下文
CoreDataManager*上下文=[CoreDataManager sharedInstance]
…
..
…
…
..…
…

---

[上下文保存上下文]

在您发布的代码中，您从未发送

NSManagedObjectContext

save消息。您所做的更改不会持久保存到

NSPersistentStore

。@alanduncan:谢谢您的重播。我可以知道如何在NSPersistentStore中持久化我的更改吗？伙计，同样的事情也发生在我身上，但是使用Visual Studio 2012和EntityFramework在VB.NET&DB=SQL Server 2012 Express中运行控制台应用程序。数据保存时使用.SaveChanges（我在每个循环结束时运行该命令，每个循环写入另一行）。现在，当我在调试模式下关闭应用程序时，数据仍然存在。没问题。但是，当我通过IDE以调试模式重新启动应用程序时，上次运行应用程序时写入的所有数据（上次执行时保存的数据）都将被删除&不再存在。快把我逼疯了。你能解决它吗？有人读了这篇文章能帮上忙吗？我也有同样的问题。我的代码适用于iOs 6.0和iOs 5.0，但不适用于iOs 7.0及更高版本。。。。你有办法解决吗？@aladuncan：：我在应用程序的生命周期中调用按钮保存操作。这不好吗？尽管使用此按钮操作保存了

NSManagedObject

上下文，还是没有保存数据？通常，当应用程序进入后台时，您还需要保存上下文。否则，当用户点击home（主页）按钮时会发生什么情况，然后你的应用程序会被杀死？您是否正在检查

save

方法的结果以确保没有错误？@aladuncan:：Yes！我检查了save方法，放置断点，逐行调试它。它很好用。每当我的应用程序启动时，都会调用retrieve方法，但它不会给出任何结果。我无法检查数据是否保存（持久化）在数据文件中。我假设，就像.NET一样，当我们使用SQL Server创建数据库时，它会创建一个SQL Server DB文件，计算该文件的大小，我可以检查该文件是否不保存数据。所以在iOS中，有没有类似于.NET的东西？我使用了NSLog和调试器工具。应用程序在运行时工作正常，它保存数据，检索数据，但当我重新启动它时，所有数据都消失了。NSPersistant存储中的更改通常在app delegate.m中，当您如上所示由另一个人保存到上下文时，它将与app delegate.m文件一起保存；您是否介意在app delegate.m文件中显示代码以及显式保存的位置。我很乐意提供帮助，但我需要查看这两部分的代码。使用NSLog做得很好。这是一种很好的调试方法，也可以使用调试器。坚持下去！：：谢谢你的回答，我真的很抱歉很晚才重播你。我已经用appDelegate.m代码更新了我的问题。请查看appDelegate.m部分。我明确保存的部分是保存数据的方法，我已经在顶部提到过。