Question

我有一个使用核心数据框架的应用程序，我对它很新。当我输入关于“pilot”的信息并保存它时，该实体的NSLog返回null，我无法弄清楚为什么他们不保存任何帮助将不胜感激。

#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>
#import <Foundation/Foundation.h>
#import "Pilot.h"




@interface PilotViewController : UIViewController <UIImagePickerControllerDelegate, UINavigationControllerDelegate,UIPopoverControllerDelegate, ABPeoplePickerNavigationControllerDelegate>







@property (weak, nonatomic       ) IBOutlet UITextField                 *nameField;
@property (weak, nonatomic       ) IBOutlet UITextField                 *phoneField;
@property (weak, nonatomic       ) IBOutlet UITextField                 *insuranceField;
@property (weak, nonatomic       ) IBOutlet UITextField                 *emailField;




@property (strong                ) NSManagedObject                      *pilot;



- (IBAction)cancel:(id)sender;
- (IBAction)save:(id)sender;




#import "PilotViewController.h"

@interface PilotViewController ()


@end

@implementation PilotViewController
@synthesize pilot;




#pragma mark Core Data Managed Object

- (NSManagedObjectContext *)managedObjectContext {
    NSManagedObjectContext *context = nil;
    id delegate                     = [[UIApplication sharedApplication] delegate];
    if ([delegate performSelector:@selector(managedObjectContext)]) {
        context                         = [delegate managedObjectContext];
    }
    return context;
}

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self                            = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization



    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


#pragma mark Save and Cancel Buttons

- (IBAction)cancel:(id)sender {
    [self dismissViewControllerAnimated:YES completion:nil];
}

- (IBAction)save:(id)sender {
    NSManagedObjectContext *context = [self managedObjectContext];

    if (self.pilot) {


        //Update existing pilot information

        [self.pilot setValue:self.nameField.text forKey:@"pilotName"];
        [self.pilot setValue:self.phoneField.text forKey:@"pilotPhone"];
        [self.pilot setValue:self.insuranceField.text forKey:@"pilotInsurance"];
        [self.pilot setValue:self.emailField.text forKey:@"pilotEmail"];



    } else {


        // Create a new managed object
        NSManagedObject *newPilot       = [NSEntityDescription insertNewObjectForEntityForName:@"Pilot" inManagedObjectContext:context];

        [newPilot setValue:self.nameField.text forKey:@"pilotName"];
        [newPilot setValue:self.phoneField.text forKey:@"pilotPhone"];
        [newPilot setValue:self.insuranceField.text forKey:@"pilotInsurance"];
        [newPilot setValue:self.emailField.text forKey:@"pilotEmail"];
        {
        NSString *pilotName = [pilot valueForKey:@"pilotName"];
            NSLog( @"%@",pilotName);

        //NSLog(@"Value of pilotName = %@",pilot);
            }

    NSError *error                  = nil;
    // Save the object to persistent store
    if (![context save:&error]) {
        NSLog(@"Can't Save! %@ %@", error, [error localizedDescription]);


    [self dismissViewControllerAnimated:YES completion:nil];
}
}
}
@end

Answer 1

似乎您的托管对象上下文为零。你为什么一开始就把它设置为零？检索它的正确方法是确保将应用代理强制转换为您的应用代理：

AppDelegate *delegate = (AppDelegate*) [[UIApplication sharedApplication] delegate];
return delegate.manageObjectContext;

Apple推荐的模式不使用app delegate。您应该为上下文提供@property上下文，并从呈现视图控制器传递上下文（例如，在prepareForSegue中）。

核心数据不节省

1 个答案: