Question

使用核心数据，如何初始化IVAR值？ Analyzer给出了错误“消息表达式中的接收器是未初始化的值”

以下是我的代码片段，用于调用在分析器中引发问题的对象：

CDCamera *camForAnnotation;

for(CDCamera *cams in fetchedObjects){  

    NSSet *annotSet = cams.annotation;

    for (CDAnnotations *myannos in annotSet){           

        if (annotationIdentifer == [myannos objectID]) {
            // found camera for annotation
            camForAnnotation = cams;
            bearing = myannos.bearing;
            break;
        }

    }               

}
double aov =  [camForAnnotation.aov doubleValue] //Receiver in message expression is an uninitialized value

这是我的CDCamera .h：

#import <CoreData/CoreData.h>

@class CDAnnotations;

@interface CDCamera :  NSManagedObject  
{
}
@property (nonatomic, retain) NSString * notes;
@property (nonatomic, retain) NSNumber * lfl;
@property (nonatomic, retain) NSNumber * ccd_h;
@property (nonatomic, retain) NSNumber * aov;
@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) NSNumber * monitor_d_size;
@property (nonatomic, retain) NSSet* annotation;

@end


@interface CDCamera (CoreDataGeneratedAccessors)
- (void)addAnnotationObject:(CDAnnotations *)value;
- (void)removeAnnotationObject:(CDAnnotations *)value;
- (void)addAnnotation:(NSSet *)value;
- (void)removeAnnotation:(NSSet *)value;
- (NSManagedObjectID *) getNSManagedObjectID;
@end

这是我的.m

#import "CDCamera.h"
#import "CDAnnotations.h"

@implementation CDCamera 

@dynamic notes;
@dynamic lfl;
@dynamic ccd_h;
@dynamic aov;
@dynamic name;
@dynamic monitor_d_size;
@dynamic annotation;

- (NSManagedObjectID *) getNSManagedObjectID{

    return [self objectID];

}

@end

感谢您的帮助。

Answer 1

如果for循环中没有任何内容匹配，则无法保证在camForAnnotation中有值。

在声明它时应该将值初始化为nil，并且可能将后续代码包装在if语句中以保存运行任何内容，如果camForAnnotation仍为nil。

Answer 2

菲尔，

Core Data具有在获取对象时调用的方法。这些用于自定义初始化。 -awakeFromFetch，-awakeFromInsert和-awakeFromSnapshotEvents:是您应该检查的方法。

安德鲁

核心数据 - 消息表达式中的接收器是未初始化的值

2 个答案: