盖伊希望你没事。
我是iPhone开发的新手。我正在使用核心数据创建一个简单的应用程序在我保存数据的应用程序期间，它工作正常，然后我检索数据，它也工作正常。但是，当我重新启动应用程序时，所有数据都将丢失。
在启动应用程序时，在ViewDidLoad函数中，我正在检索具有在工作应用程序中检索的相同功能的数据。
保存数据方法：
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];
}
检索数据方法：
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
这里有什么不对吗？ 我希望尽早得到好的答案。
答案 0 :(得分：6)
在应用程序的生命周期的某个时刻，您需要在save上致电NSManagedObjectContext，否则您的更改将不会保留到NSPersistentStore。例如，在应用程序委托的applicationDidEnterBackground:方法中。
NSError *saveError = nil;
if( ![[self managedObjectContext] save:&saveError] ) {
// deal with error...
}
我假设您的应用程序委托设置并维护核心数据堆栈，就像Apple模板一样......
答案 1 :(得分：4)
在AppDelegate中：
- (void)applicationWillTerminate:(UIApplication *)application
{
// Saves changes in the application's managed object context before the application terminates.
[self saveContext];
}
早期版本的Xcode模板中的-saveContext可能是-save。
而且，您可以在其他类中调用-save或-saveContent方法：
[(AppDelegate *)[UIApplication sharedApplication] saveContext];
答案 2 :(得分：0)
我没有看到您将保存放在代码中的位置。您需要告知managedcontext要保存。你这样做取决于你的应用程序和设计。如果您认为它已经在您的应用程序中某处添加了一些NSLog来尝试调试或使用调试工具来实际进入您的代码。
这是一个简单的解决方案。祝你好运。
答案 3 :(得分：0)
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NSManagedObjectContext所做的任何更改都是临时的。尝试将此添加到方法的末尾：
if (![context save:&error]) {
NSLog(@"Couldn't save: %@", error);
}
答案 4 :(得分：0)
需要保存此上下文
CoreDataManager * context = [CoreDataManager sharedInstance];
...
..
...
...
.....
...
[context saveContext];