Question

运行我的应用程序时，我不断收到此错误：“CoreData：错误：无法在NSManagedObject类上调用指定的初始化程序”Ambulance“”。我已经在堆栈溢出上看到了这个问题，但我不确定如何在我的情况下实现解决方案。有什么想法吗？

Ambulance.h

#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>


@interface Ambulance : NSManagedObject

@property (nonatomic, retain) NSString * ambulanceID;
@property (nonatomic, retain) NSNumber * distance;
@property (nonatomic, retain) NSNumber * etaDistance;
@property (nonatomic, retain) NSString * emsID;
@property (nonatomic, retain) NSString * lat;
@property (nonatomic, retain) NSString * lng;
@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) NSNumber * occupancy;
@property (nonatomic, retain) NSString * type;
@property (nonatomic, retain) NSString * websocketServer;
@property (nonatomic, retain) NSNumber * seconds;
@property (nonatomic, retain) id eta;

+(Ambulance *)nearestAmbulanceByType:(NSString *)type;


- (id)initWithCoder:(NSCoder *)decoder;
- (void)encodeWithCoder:(NSCoder *)encoder;


@end

Ambulance.m

#import "Ambulance.h"


@implementation Ambulance

@synthesize ambulanceID;
@synthesize distance;
@synthesize etaDistance;
@synthesize emsID;
@synthesize lat;
@synthesize lng;
@synthesize name;
@synthesize occupancy;
@synthesize type;
@synthesize websocketServer;
@synthesize seconds;
@synthesize eta;


+(Ambulance *)nearestAmbulanceByType:(NSString *)type {
NSArray *sortedArray = [Ambulance findByAttribute:@"type" withValue:type         andOrderBy:@"distance" ascending:YES];
return [sortedArray first];
 }


  - (void)encodeWithCoder:(NSCoder *)encoder {
//Encode properties, other class variables, etc
[encoder encodeObject:self.ambulanceID forKey:@"ambulanceID"];
[encoder encodeObject:self.distance forKey:@"distance"];
[encoder encodeObject:self.etaDistance forKey:@"etaDistance"];
[encoder encodeObject:self.emsID forKey:@"emsID"];
[encoder encodeObject:self.lat forKey:@"lat"];
[encoder encodeObject:self.lng forKey:@"lng"];
[encoder encodeObject:self.name forKey:@"name"];
[encoder encodeObject:self.occupancy forKey:@"occupancy"];
[encoder encodeObject:self.type forKey:@"type"];
[encoder encodeObject:self.websocketServer:@"websocketServer"];
[encoder encodeObject:self.seconds forKey:@"seconds"];
[encoder encodeObject:self.eta forKey:@"eta"];

}

- (id)initWithCoder:(NSCoder *)decoder {


if((self = [super init])) {
    //decode properties, other class vars


    self.ambulanceID = [decoder decodeObjectForKey:@"ambulanceID"];
    self.distance = [decoder decodeObjectForKey:@"distance"];
    self.etaDistance = [decoder decodeObjectForKey:@"etaDistance"];
    self.emsID = [decoder decodeObjectForKey:@"emsID"];
    self.lat = [decoder decodeObjectForKey:@"lat"];
    self.lng = [decoder decodeObjectForKey:@"lng"];
    self.name = [decoder decodeObjectForKey:@"name"];
    self.occupancy = [decoder decodeObjectForKey:@"occupancy"];
    self.type = [decoder decodeObjectForKey:@"type"];
    self.websocketServer = [decoder decodeObjectForKey:@"websocketServer"];
    self.seconds = [decoder decodeObjectForKey:@"seconds"];
    self.eta = [decoder decodeObjectForKey:@"eta"];

}
return self;
}

Answer 1

您应该为initWithEntity:insertIntoManagedObjectContext:子类使用除NSManagedObject之外的任何其他初始化程序。

来自文档：

重要说明：此方法是指定的初始化程序 NSManagedObject。您不能简单地初始化托管对象发送它。

您确定必须在子类中使用NSCoding吗？存储objectID可能就足够了，因为您的对象存在于NSManagedObjectContext中，并且可能会持久存在。

如果您真的依赖于NSCoding，则必须确定并将适当的NSManagedObjectContext提供给initWithEntity:insertIntoManagedObjectContext:中的initWithCoder:。

Answer 2

不确定这与RestKit有什么关系以及您认为需要支持编码的原因。

假设您正在使用RestKit，您应该能够更改为：

- (id)initWithCoder:(NSCoder *)decoder {
    NSManagedObjectContext *moc = [RKManagedObjectStore defaultStore].mainQueueManagedObjectContext;
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Ambulance" inManagedObjectContext:moc];

    if((self = [super initWithEntity:entity insertIntoManagedObjectContext:moc])) {
    ...

如果您没有使用RestKit，那么您将需要一种不同的方式来获取MOC。

CoreData：错误：使用NSCoding时无法在NSManagedObject类上调用指定的初始化程序

2 个答案: