Error : CoreData: error: Failed to call designated initializer on NSManagedObject class 'Product'

问题:

I start to use core data with ios 5. I have my product model :

Product.m :

#import "Product.h" @implementation Product     @dynamic category_id;     @dynamic label;     @dynamic price; @end 

Product.h :

#import <Foundation/Foundation.h> #import <CoreData/CoreData.h>  @interface Product : NSManagedObject    @property (nonatomic, retain) NSString *category_id;   @property (nonatomic, retain) NSString *label;   @property (nonatomic, retain) NSString *price; @end 

I try to parse an xml with a custom class using NSXMLParserDelegate. My xml looks like :

<section id="2">   <label>Animaux</label>   <image>Images/Rayons/Bandeau/Animaux.png</image>   <key>Images/Rayons/Bandeau/Animaux.png</key>   <products>      <Product id="21">         <category_id>Chat</category_id>         <label>Aliments pour chat</label>         <price>2.00</price>      </Product>      <Product id="1286">         <category_id>Chat</category_id>         <label>Boite de paté</label>         <price>0.00</price>      </Product>   </products> </sections> 

When i have a balise Product, I build my model like this :

item = [[NSClassFromString(className) alloc] init]; 

And when i have a property as category_id, i do :

[item setValue:currentNodeContent forKey:elementName]; 

And i got the error :

CoreData: error: Failed to call designated initializer on NSManagedObject class 'Product'

Any idea?

回答1:

The docs for NSManagedObject state that the dedicated intializer is:

initWithEntity:insertIntoManagedObjectContext: 

which is why that is failing. Most of the examples I have seen suggest you should get a new object like this

[NSEntityDescription entityForName:@"MyClass" inManagedObjectContext:self.managedObjectContext]]; 

So you could try something like:

[NSEntityDescription entityForName:className inManagedObjectContext:self.managedObjectContext]]; 

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