對變形屬性

Question

奇怪警告我是用變形的屬性，一切都做工精細，而不是這些警告：

15.10.11 22:14:07,191 cdtool: CoreData: warning: no NSValueTransformer with class name 'ArrayToDataTransformer' was found for attribute 'directions' on entity 'DatabaseConnections' 
15.10.11 22:14:07,191 cdtool: CoreData: warning: no NSValueTransformer with class name 'ArrayToDataTransformer' was found for attribute 'updateChoices' on entity 'DatabaseConnections' 
15.10.11 22:14:07,193 cdtool: CoreData: warning: no NSValueTransformer with class name 'ArrayToDataTransformer' was found for attribute 'testingResult' on entity 'DestinationsListWeBuy' 

可有人告訴如何走出這一警告。 當然，一切都是正確的，屬性是可選的，可轉換的。 波紋管是一個類實現：

#import <Foundation/Foundation.h> 

@interface ArrayToDataTransformer : NSValueTransformer { 

} 

@end 



#import "ArrayToDataTransformer.h" 


@implementation ArrayToDataTransformer 

+ (BOOL)allowsReverseTransformation { 
    return YES; 
} 

+ (Class)transformedValueClass { 
    return [NSData class]; 
} 

- (id)transformedValue:(id)value { 
    //Take an NSArray archive to NSData 
    NSData *data = [NSKeyedArchiver archivedDataWithRootObject:value]; 
    return data; 
} 

- (id)reverseTransformedValue:(id)value { 
    //Take NSData unarchive to NSArray 
    NSArray *array = (NSArray*)[NSKeyedUnarchiver unarchiveObjectWithData:value]; 
    return array; 
} 

@end 

Answer 1

之前，你可以叫你有註冊一個自定義的變壓器：

+[NSValueTransformer setValueTransformer:forName:] 

...否則，運行時不知道變壓器存在。