ios - 数据 : issue in another function after fetching data from core data

Question

我是 coredata 的新手，几天前我开始使用 core data。如果我以当前方法记录数据，我已经编写了一个谓词来从 coredata 中获取数据，它工作正常。如果我用另一种方法记录数据，它会显示“数据:”

<Profile: 0x16451ba0> (entity: Profile; id: 0x1633c150 <x-coredata://41971DAD-4658-4C38-9D14-7FDFFA57E032/Profile/p6> ; data: <fault>)

-(void)populateCurrentUserData{

       self.blockListArray = [self dataForJid:[[DataManager sharedHandler]userToken]];
   Profile *profile = [self.blockListArray objectAtIndex:0];
          NSLog(@"Data is :%@",profile.userId);//prints nil
      NSLog(@"Data is :%@",self.blockListArray); //"<Profile: 0x17bb23f0> (entity: Profile; id: 0x17bb1fe0 <x-coredata://41971DAD-4658-4C38-9D14-7FDFFA57E032/Profile/p1> ; data: <fault>)"

 }

-(NSArray *)dataForJid:(NSString *)inJid{
   NSArray *data = [[NSArray alloc]init];
   NSError *error;
   self.dataArray = [[NSMutableArray alloc]init];
   MKAUserProfileCoreData *storage = [[MKAUserProfileCoreData alloc]init];
   NSManagedObjectContext *moc = [storage managedObjectContext];
   NSEntityDescription *entity = [NSEntityDescription   entityForName:@"Profile" inManagedObjectContext:moc];
   NSFetchRequest *request = [[NSFetchRequest alloc]init];
   NSPredicate *profilePredicate = [NSPredicate predicateWithFormat:@"userId = %@", inJid];
   [request setPredicate:profilePredicate];
   [request setEntity:entity];
   [request setReturnsObjectsAsFaults:NO];
   data = [moc executeFetchRequest:request error:&error];
   NSLog(@"Data is :%@",data); //This log works fine

return data;

/.h
#import <Foundation/Foundation.h>

 @interface MKAUserProfileCoreData : NSObject
{
 NSManagedObjectModel *managedObjectModel;
 NSManagedObjectContext *managedObjectContext;
 NSPersistentStoreCoordinator *persistentStoreCoordinator;
}
@property (nonatomic, strong, readonly) NSManagedObjectModel *managedObjectModel;
@property (nonatomic, strong, readonly) NSManagedObjectContext   *managedObjectContext;
@property (nonatomic, strong, readonly) NSPersistentStoreCoordinator *persistentStoreCoordinator;
@end

/.m


 #import "MKAUserProfileCoreData.h"
 #import <CoreData/CoreData.h>

 @implementation MKAUserProfileCoreData
- (NSManagedObjectContext *) managedObjectContext {

 if (managedObjectContext != nil) {
    return managedObjectContext;
 }

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

   - (NSManagedObjectModel *)managedObjectModel {

   if (managedObjectModel != nil) {
    return managedObjectModel;
  }
   managedObjectModel = [NSManagedObjectModel mergedModelFromBundles:nil];
   return managedObjectModel;
}





  - (NSPersistentStoreCoordinator *)persistentStoreCoordinator {

  if (persistentStoreCoordinator != nil) {
    return persistentStoreCoordinator;
  }

 NSURL *storeUrl = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory] stringByAppendingPathComponent: @"splashUserProfile.sqlite"]];

NSError *error = nil;
persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc]
                              initWithManagedObjectModel:[self managedObjectModel]];
if (![persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType
                                              configuration:nil URL:storeUrl options:@{NSMigratePersistentStoresAutomaticallyOption:@YES, NSInferMappingModelAutomaticallyOption:@YES} error:&error]) {
    NSLog(@"Error is %@",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. If it is not possible to recover from the error, display an alert panel that
     instructs the user to quit the application by pressing the Home button.

     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.
     */
    abort();
   }

   return persistentStoreCoordinator;
}

 - (NSString *)applicationDocumentsDirectory {
NSString *path = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,  NSUserDomainMask, YES) lastObject];
//NSLog(@"Path is %@", path);
return path;
 }

 @end

Answer 1

问题是 storage 和 moc 都是在 dataForJid: 中本地创建的。当该方法完成时，这两个变量都将被释放。因此 NSManagedObjects 变得无效。您需要保持对 CoreData 堆栈的强引用 - 例如，将 MKAUserProfileCoreData 设为单例，或者直接在 View Controller 中构建堆栈。