字典、数组和json字符串的相互转化

+ (nullable id)JSONObjectWithData:(NSData *)data options:(NSJSONReadingOptions)opt error:(NSError **)error;

+ (nullable NSData *)dataWithJSONObject:(id)obj options:(NSJSONWritingOptions)opt error:(NSError **)error;

//将jsonString转化为字典
- (NSDictionary *)transformStringIntoDictionary:(NSString *)jsonString {
//先将jsonString转化为NSData类型数据
NSData *data = [jsonString dataUsingEncoding:NSUTF8StringEncoding];

NSError *error;

//将NSData类型转化为NSDictionary类型，也可以转化为NSArray类型
NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:&error];

return dic;
}

//将字典／数组转化为jsonString
- (NSString *)transformDictionaryIntoString:(NSDictionary *)dictionary {

NSError *error;

//先将NSDictonary转化为NSData类型
NSData *data = [NSJSONSerialization dataWithJSONObject:dictionary options:NSJSONWritingPrettyPrinted error:&error];

//再把NSdata类型转化为String类型
NSString *jsonString = [[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding];

return jsonString;
}