*)URLJSONTransformer { return [NSValueTransformer valueTransformerForName:MTLURLValueTransformerName ]; } + (NSValueTransformer *)HTMLURLJSONTransformer { return [NSValueTransformer valueTransformerForName:MTLURLValueTransformerName]; } + (NSValueTransformer *)stateJSONTransformer { return [NSValueTransformer mtl_valueMappingTransformerWithDictionary:@{ @"open ": @(GHIssueStateOpen), @"closed": @(GHIssueStateClosed) }]; } + (NSValueTransformer
You access an attribute as a non-standard type, but behind the scenes Core Data uses an instance of NSValueTransformer
- (void)layout; // 计算布局 @end MVideo.m #import "MVideo.h" #import "MTLValueTransformer.h" #import "NSValueTransformer
NSCoding协议并实现required方法(initWithCoder:方法和encodeWithCoder:方法); xcdatamodeld文件中该特性数据类型选择为Transformable 创建一个NSValueTransformer