Data lost during application restart (master data)

Question

I hope everything will be fine with you.

I am new to iPhone development. I am creating a simple application using basic data. During the application, when I save the data, it works fine, and then I retrieve the data, it also works fine. But when I restart the application, all data is lost.

When I run the application in the ViewDidLoad function, I get data with the same function that I retrieve during the working application.

Saving data method:

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]; } 

Extract data method:

  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]; 

Application Delegation Code

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

Is something wrong here? I hope to get good answers as early as possible.

Answer 1

At some point in the application life cycle, you need to call save in NSManagedObjectContext , or your changes will not be saved to NSPersistentStore . For example, in delegate deletion applicationDidEnterBackground:

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

I assume that your application delegate installs and supports the Core Data stack, for example, Apple templates ...

Answer 2

In the AppDelegate app:

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

-saveContext may be -save in an earlier version of the Xcode template.

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And what more, you can simply call the -save or -saveContent in other classes:

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

Answer 3

I do not see where you put the save in code. You need to specify a managed context to save. Where you do this depends on your application and design. If you think this is already in your applications, add some NSLog to try and debug or use a debugger tool to actually enter your code.

This is easy to fix. Good luck.

Answer 4

NSManagedObjectContext provides a notepad: you can do whatever you want with your objects, but you need to keep it at the end. Any changes you make to the NSManagedObjectContext are temporary until you save them. Try adding this to the end of your method:

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

Answer 5

this context needs to be maintained
CoreDataManager * context = [CoreDataManager sharedInstance];
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[context saveContext];