核心数据不保存

Posted 2023-03-12

【中文标题】核心数据不保存

【英文标题】：Core Data Not Saving

【发布时间】：2014-08-17 13:42:29

【问题描述】：

我有一个使用核心数据框架的应用程序，我对它还很陌生。当我输入有关“飞行员”的信息并将其保存时，该实体的 NSLog 返回 null，我无法弄清楚他们为什么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

【问题讨论】：

欢迎来到 SOF。不鼓励代码“倾销”。你应该只发布你不确定的代码。

我认为您的意思是 respondsToSelector 不是 performSelector。但是，我怀疑这会解决您的问题。

我们可以看到您在应用委托中设置托管对象上下文的位置吗？

更改为respondsToSelector很重要，因为如果代理没有该选择器并且您尝试在代理上执行该选择器，您的应用程序将会崩溃。你会得到这些坏男孩之一，-[AppDelegate managedObjectContext]: unrecognized selector sent to instance <your_instance>

【参考方案1】：

似乎您的托管对象上下文为零。你为什么首先将它设置为零？检索它的正确方法是确保将应用委托转换为您的应用委托：

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

Apple 推荐的模式不使用应用委托。您应该为您的班级提供一个 @property 作为上下文，并从呈现视图控制器传递上下文（例如在 prepareForSegue 中）。

【讨论】：

那么在我有 = nil 的地方，我应该有应用委托吗？

他们在哪里将上下文设置为零？我没看到。他们似乎只是在初始化 ManagedObjectContext 指针。此外，尚不清楚他们是否在托管对象上下文中设置了持久化。

@user3927993 不，你的问题没有意义。也许你对此有点过头了。