-(NSString*)countryNameByCode:(NSString*)countryCode{NSString*identifier=[NSLocalelocaleIdentifierFromComponents:@{NSLocaleCountryCode:countryCode}];NSString*countryName=[[NSLocalecurrentLocale]displayNameForKey:NSLocaleIdentifiervalue:identifier];returncountryName;}这返回了nil。为什么？ 最佳

-(NSString*)countryNameByCode:(NSString*)countryCode{NSString*identifier=[NSLocalelocaleIdentifierFromComponents:@{NSLocaleCountryCode:countryCode}];NSString*countryName=[[NSLocalecurrentLocale]displayNameForKey:NSLocaleIdentifiervalue:identifier];returncountryName;}这返回了nil。为什么？ 最佳