使用 CoreData 的 UITableViewController class 中的 NSManagedObjectContext 为 nil
NSManagedObjectContext is nil in the UITableViewController class using CoreData
我需要在 CoreData 的 UITableViewController 中显示一些元素,但是 NSManagedObjectContext 实例(称为 *managedObjectContext)在应用程序启动时为 nil。
这是我的UITableViewController.h
@interface TableViewController : UITableViewController
@property(nonatomic,strong) NSArray *listaElementi;
@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext; //si occupa di gestire come sono strutturate le entity
@end
这是我的UITableViewController.m
- (void)viewDidLoad {
[super viewDidLoad];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
entityForName:@"Stato" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
NSError *error;
self.listaElementi = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
self.title = @"Stati";
最后这是我的 AppDelegate.m
@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;
- (NSManagedObjectModel *)managedObjectModel {
// The managed object model for the application. It is a fatal error for the application not to be able to find and load its model.
if (_managedObjectModel != nil) {
return _managedObjectModel;
}
NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Model" withExtension:@"momd"]; //SETTARE BENE IL MODELLO
_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
return _managedObjectModel;
}
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
// The persistent store coordinator for the application. This implementation creates and return a coordinator, having added the store for the application to it.
if (_persistentStoreCoordinator != nil) {
return _persistentStoreCoordinator;
}
// Create the coordinator and store
_persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Database.sqlite"];
NSError *error = nil;
NSString *failureReason = @"There was an error creating or loading the application's saved data.";
if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
// Report any error we got.
NSMutableDictionary *dict = [NSMutableDictionary dictionary];
dict[NSLocalizedDescriptionKey] = @"Failed to initialize the application's saved data";
dict[NSLocalizedFailureReasonErrorKey] = failureReason;
dict[NSUnderlyingErrorKey] = error;
error = [NSError errorWithDomain:@"YOUR_ERROR_DOMAIN" code:9999 userInfo:dict];
// Replace this 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();
}
return _persistentStoreCoordinator;
}
- (NSManagedObjectContext *)managedObjectContext {
// Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.)
if (_managedObjectContext != nil) {
return _managedObjectContext;
}
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (!coordinator) {
return nil;
}
_managedObjectContext = [[NSManagedObjectContext alloc] init];
[_managedObjectContext setPersistentStoreCoordinator:coordinator];
return _managedObjectContext;
}
你能帮帮我吗?当我创建项目时,我没有选中添加核心数据框,但是我手动实现了所有,我只是创建了模型,我只是在数据库中插入了一些元素,这可能是问题的原因吗?
在 viewDidLoad 中试试这个
<pre>
- (void)viewDidLoad {
[super viewDidLoad];
AppDelegate *delgate = (AppDelegate *)[[UIApplication
sharedApplication]delegate];
self.managedObjectContext = delegate.managedObjectContext;
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
entityForName:@"Stato" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
NSError *error;
self.listaElementi = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];</p>
<p>}
</pre>
我需要在 CoreData 的 UITableViewController 中显示一些元素,但是 NSManagedObjectContext 实例(称为 *managedObjectContext)在应用程序启动时为 nil。
这是我的UITableViewController.h
@interface TableViewController : UITableViewController
@property(nonatomic,strong) NSArray *listaElementi;
@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext; //si occupa di gestire come sono strutturate le entity
@end
这是我的UITableViewController.m
- (void)viewDidLoad {
[super viewDidLoad];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
entityForName:@"Stato" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
NSError *error;
self.listaElementi = [managedObjectContext executeFetchRequest:fetchRequest error:&error];
self.title = @"Stati";
最后这是我的 AppDelegate.m
@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;
- (NSManagedObjectModel *)managedObjectModel {
// The managed object model for the application. It is a fatal error for the application not to be able to find and load its model.
if (_managedObjectModel != nil) {
return _managedObjectModel;
}
NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Model" withExtension:@"momd"]; //SETTARE BENE IL MODELLO
_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
return _managedObjectModel;
}
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
// The persistent store coordinator for the application. This implementation creates and return a coordinator, having added the store for the application to it.
if (_persistentStoreCoordinator != nil) {
return _persistentStoreCoordinator;
}
// Create the coordinator and store
_persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Database.sqlite"];
NSError *error = nil;
NSString *failureReason = @"There was an error creating or loading the application's saved data.";
if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
// Report any error we got.
NSMutableDictionary *dict = [NSMutableDictionary dictionary];
dict[NSLocalizedDescriptionKey] = @"Failed to initialize the application's saved data";
dict[NSLocalizedFailureReasonErrorKey] = failureReason;
dict[NSUnderlyingErrorKey] = error;
error = [NSError errorWithDomain:@"YOUR_ERROR_DOMAIN" code:9999 userInfo:dict];
// Replace this 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();
}
return _persistentStoreCoordinator;
}
- (NSManagedObjectContext *)managedObjectContext {
// Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.)
if (_managedObjectContext != nil) {
return _managedObjectContext;
}
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (!coordinator) {
return nil;
}
_managedObjectContext = [[NSManagedObjectContext alloc] init];
[_managedObjectContext setPersistentStoreCoordinator:coordinator];
return _managedObjectContext;
}
你能帮帮我吗?当我创建项目时,我没有选中添加核心数据框,但是我手动实现了所有,我只是创建了模型,我只是在数据库中插入了一些元素,这可能是问题的原因吗?
在 viewDidLoad 中试试这个
<pre>
- (void)viewDidLoad {
[super viewDidLoad];
AppDelegate *delgate = (AppDelegate *)[[UIApplication
sharedApplication]delegate];
self.managedObjectContext = delegate.managedObjectContext;
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
entityForName:@"Stato" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
NSError *error;
self.listaElementi = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];</p>
<p>}
</pre>