Question

我收到JSON格式的回复，过去从未解析过，所以有人可以帮我理解这一点。这是我得到的Json回应：

Twitter回复：

(
    {
        contributors = "<null>";
        coordinates = "<null>";
        "created_at" = "Tue Nov 29 15:48:35 +0000 2011";
        entities =         {
            hashtags =             (
            );
            media =             (
                                {
                    "display_url" = "pic.twitter.com/650E1WRY";
                    "expanded_url" = "http://twitter.com/ashu1702/status/141544088850796545/photo/1";
                    id = 141544088854990848;
                    "id_str" = 141544088854990848;
                    indices =                     (
                        22,
                        42
                    );
                    "media_url" = "http://p.twimg.com/AfbdmVBCEAAPJvT.jpg";
                    "media_url_https" = "https://p.twimg.com/AfbdmVBCEAAPJvT.jpg";
                    sizes =                     {
                        large =                         {
                            h = 279;
                            resize = fit;
                            w = 215;
                        };
                        medium =                         {
                            h = 279;
                            resize = fit;
                            w = 215;
                        };
                        small =                         {
                            h = 279;
                            resize = fit;
                            w = 215;
                        };
                        thumb =                         {
                            h = 150;
                            resize = crop;
                            w = 150;
                        };
                    };
                    type = photo;
                    url = "http://t.co/650E1WRY";
                }
            );
            urls =             (
            );
            "user_mentions" =             (
            );
        };
        favorited = 0;
        geo = "<null>";
        id = 141544088850796545;
        "id_str" = 141544088850796545;
        "in_reply_to_screen_name" = "<null>";
        "in_reply_to_status_id" = "<null>";
        "in_reply_to_status_id_str" = "<null>";
        "in_reply_to_user_id" = "<null>";
        "in_reply_to_user_id_str" = "<null>";
        place = "<null>";
        "possibly_sensitive" = 0;
        "retweet_count" = 0;
        retweeted = 0;
        source = "<a href=\"http://www.apple.com\" rel=\"nofollow\">iOS</a>";
        text = "I am in Syria @(null) http://t.co/650E1WRY";
        truncated = 0;
        user =         {
            "contributors_enabled" = 0;
            "created_at" = "Sun May 01 15:20:52 +0000 2011";
            "default_profile" = 1;
            "default_profile_image" = 1;
            description = "<null>";
            "favourites_count" = 0;
            "follow_request_sent" = "<null>";
            "followers_count" = 0;
            following = "<null>";
            "friends_count" = 5;
            "geo_enabled" = 0;
            id = 291164338;
            "id_str" = 291164338;
            "is_translator" = 0;
            lang = en;
            "listed_count" = 0;
            location = "<null>";
            name = "Ashutosh Tiwari";
            notifications = "<null>";
            "profile_background_color" = C0DEED;
            "profile_background_image_url" = "http://a0.twimg.com/images/themes/theme1/bg.png";
            "profile_background_image_url_https" = "https://si0.twimg.com/images/themes/theme1/bg.png";
            "profile_background_tile" = 0;
            "profile_image_url" = "http://a2.twimg.com/sticky/default_profile_images/default_profile_3_normal.png";
            "profile_image_url_https" = "https://si0.twimg.com/sticky/default_profile_images/default_profile_3_normal.png";
            "profile_link_color" = 0084B4;
            "profile_sidebar_border_color" = C0DEED;
            "profile_sidebar_fill_color" = DDEEF6;
            "profile_text_color" = 333333;
            "profile_use_background_image" = 1;
            protected = 0;
            "screen_name" = ashu1702;
            "show_all_inline_media" = 0;
            "statuses_count" = 62;
            "time_zone" = "<null>";
            url = "<null>";
            "utc_offset" = "<null>";
            verified = 0;
        };
    }
)

具体来说，我只需要“expanded_url”，我在我的代码中这样做就可以了：

NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:responseData options:0 error:&error];// where response data is coming from the call made to twitter timeline_api

                          NSString * callBackURL = [dict objectForKey:@"expanded_url"];

在执行此操作时，我收到此错误：

2011-11-29 09:50:31.214 L'Occitane[1119:19d07] -[__NSCFArray objectForKey:]: unrecognized selector sent to instance 0x85a50d0
2011-11-29 09:50:31.215 L'Occitane[1119:19d07] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFArray objectForKey:]: unrecognized selector sent to instance 0x85a50d0'

请帮助!!!

谢谢，

Answer 1

转换为Cocoa Foundation对象时，JSON会分解为一堆嵌套的NSArrays和NSDictionary，最终导致NSString s，NSNumber和{{1} }秒。理想情况下，您可以从Web服务的文档向前工作，但您可以从根对象通过NSNull打印的描述向后工作。

从日志中我可以看到NSLog是未命名对象的成员，该对象是expanded_url数组中第一个media对象成员的条目。包含entities的未命名对象是数组的一部分，这是JSON反序列化器将返回的内容。所以你想要做类似的事情（如果以长篇形式写出来进行展示，并且没有任何验证）：

entities

主要的风险是Web服务可能会为NSArray *result = [NSJSONSerialization ... NSDictionary *firstObject = [result objectAtIndex:0]; NSDictionary *entities = [firstObject objectForKey:@"entities"]; NSArray *media = [entities objectForKey:@"media"]; NSDictionary *relevantObject = [media objectAtIndex:0]; NSString *expandedUrl = [relevantObject objectForKey:@"expanded_url"];返回一个空数组，导致media引发异常，或者它将返回除数组以外的其他内容作为根对象或以某种其他方式调整沿线某处的类型。 Objective-C关于消息传递objectAtIndex:0的通常规则应该可以避免大多数字典问题。相当多的验证适用于判断调用。

如何从JSON获取数据？

1 个答案: