Question

我创建了一个链接到saveButton的IBAction，当我在IBAction中调用所有核心数据方法时，它可以在以下代码中正常工作：

- (IBAction)saveButtonTap:(id)sender{
    NSManagedObjectContext *context = [self managedObjectContext];
    NSManagedObject *object = [NSEntityDescription insertNewObjectFor:@"Person" inManagedContext:context];

    [self setValue:firstNameTextField.text forKey:@"firstName"];
    [self setValue:lastNameTextField.text  forKey:@"lastName"];

    NSError *error   = nil;
    if (![context save:&error])
        NSLog(@"Can't save transaction - %@ || %@ ", error, [error localizedDescription]);

}

当我将核心数据保存方法分离如下时，保存的firstName和lastName，在获取时显示为null。它没有返回错误，但我在谷歌搜索一整天后都不知道。有人能指出我的代码有什么问题吗？

Person.h + Person.m

@interface Person : NSManagedObject

@property(strong) NSString *firstName;
@property(strong) NSString *lastName;

- (void)save;
@end

@implementation Person

@synthesize firstName;
@synthesize lastName;

- (void)save{
    [self setValue:self.firstName forKey:@"firstName"];
    [self setValue:self.lastName  forKey:@"lastName"];
}
@end

mainViewController.h + mainViewController.m

@interface mainViewController : UIViewController

@property(strong) ManagedObjectContext *context;
@property(strong) Person *person;

- (IBAction)saveButtonTap:(id)sender;
@end

@implementation mainViewController

@synthesize context;
@synthesize person;

- (void)viewDidLoad{
    // ... some view did Load rituals
    if(context == nil){
        context = [self managedObjectContext]; // Assume this method calls for managed object context from shared application.
    }

    if(person == nil){
        person = [NSEntityDescription insertNewObjectFor:@"Person" inManagedContext:context];
    }
}

- (IBAction)saveButtonTap:(id)sender{

    person.firstName = firstNameTextField.text;
    person.lastName  = lastNameTextField.text;

    [self.person save];

    NSError *error   = nil;
    if (![context save:&error])
        NSLog(@"Can't save transaction - %@ || %@ ", error, [error localizedDescription]);
}
@end

Answer 1

Person不需要保存功能。

person.firstName = firstNameTextField.text

相当于

[self setValue：self.firstName forKey：@“firstName”];

你需要的是这样的：

（IBAction为）saveButtonTap：（ID）发送方{

person.firstName = firstNameTextField.text;

person.lastName = lastNameTextField.text;

NSError * error = nil;

if（！[context save：＆amp; error]）
NSLog(@"Can't save transaction - %@ || %@ ", error, [error localizedDescription]);
}

但是，我不确定这是否是问题的原因。试试吧，让我知道。

获取托管对象返回null

1 个答案: