NSManagedObjectContext，声明在哪里？

Question

对不起，接下来的新事物。非常感谢您的耐心。

当添加一个新的对象，以核心数据，正确的初始化是这样的：

- (id)initWithEntity:(NSEntityDescription *)entity insertIntoManagedObjectContext: (NSManagedObjectContext *)context 

好，所以initWithEntity部分我明白了。我的核心数据模型中只有一个实体，所以我把它放在那里。上下文是我困惑的地方。首先，在哪里声明上下文，还是我需要声明它？只需键入self.ManagedObjectContext不起作用，也不自动完成。也许因为我试图从我的AddViewController中调用此方法是原因，所以即使我输入Car.ManagedObjectContext或AppDelegate.ManagedObjectContext也会发生同样的情况。我猜我可以在我的care-data生成的模型类（Car.h）中声明它，但它实际上做了什么？

我在这里不理解什么？对于新问题抱歉。我真的一直在想这个问题好几个小时。

这是我的代码。

car.h：

@interface Car : NSManagedObject 

@property (nonatomic, retain) NSString * brand; 
@property (nonatomic, retain) NSString * model; 
@property (nonatomic, retain) NSString * year; 
@property (nonatomic, retain) NSString * color; 
@property (nonatomic, retain) NSNumber * engineSize; 
@property (nonatomic, retain) NSNumber * weight; 
@property (nonatomic, retain) id image; 

@end 

car.m: 

#import "Car.h" 


@implementation Car 

@dynamic brand; 
@dynamic model; 
@dynamic year; 
@dynamic color; 
@dynamic engineSize; 
@dynamic weight; 
@dynamic image; 

@end 

addViewController.h（不包括AppDelegate的，因为这一切都非常标准，似乎很好地工作我所做的编码是在addview控制器）：

#import <Cocoa/Cocoa.h> 

@interface AddViewController : NSWindowController{ 
    } 

@property (weak) IBOutlet NSTextField *brandField; 
@property (weak) IBOutlet NSTextField *modelField; 
@property (weak) IBOutlet NSTextField *yearField; 
@property (weak) IBOutlet NSTextField *weightField; 
@property (weak) IBOutlet NSTextField *engineSizeField; 
@property (weak) IBOutlet NSTextField *colorField; 
@property (weak) IBOutlet NSImageView *imageField; 


- (IBAction)saveCar:(id)sender; 

@end 

AddViewController.m: 


#import "AddViewController.h" 
#import "AppDelegate.h" 
#import "Car.h" 
@interface AddViewController() 

@end 

@implementation AddViewController 
@synthesize brandField; 
@synthesize modelField; 
@synthesize yearField; 
@synthesize engineSizeField; 
@synthesize weightField; 
@synthesize colorField; 
@synthesize imageField; 



- (id)initWithWindow:(NSWindow *)window 
{ 
    self = [super initWithWindow:window]; 
    if (self) { 
     // Initialization code here. 
    } 

    return self; 
} 

- (void)windowDidLoad 
{ 
    [super windowDidLoad]; 

    // Implement this method to handle any initialization after your window controller's window has been loaded from its nib file. 
} 

- (IBAction)saveCar:(id)sender { 
    NSManagedObjectContext *context = [Car managedObjectContext]; //This doesn't work here "no known class method" 


    Car *newCar = [[Car alloc] initWithEntity:@"Car" insertIntoManagedObjectContext:Car.managedObjectContext]; //compiler complains about this, property not found. 


    newCar.brand = [brandField stringValue]; 
    newCar.model = [modelField stringValue]; 
    newCar.year = [yearField stringValue]; 
    newCar.weight = [weightField objectValue]; 
    newCar.engineSize = [engineSizeField objectValue]; 
    newCar.color = [colorField stringValue]; 
    newCar.image = imageField; 


} 


@end 

Answer 1

您需要创建一个managedObjectContext。 它通常在appDelegate中完成。 苹果有一篇很好的文章：Apple documentation