iOS NSDictionary <--> NSString(JSON) in Objc

+ (NSString*)stringINJSONFormatForObject:(id)obj
{
    NSData *jsonData = [NSJSONSerialization dataWithJSONObject:obj
                                                       options:0 // If that option is not set, the most compact possible JSON will be generated
                                                         error:nil];

    NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
    jsonString = [jsonString stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];  //去除掉首尾的空白字符和换行字符

    return jsonString;
}

+ (NSDictionary *)dictForJSONString:(NSString *)str
{
    NSData *jsonData = [str dataUsingEncoding:NSUTF8StringEncoding];
    NSError *err;
    NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:jsonData
                                                        options:NSJSONReadingMutableContainers
                                                          error:nil];
    return dic;
}