json(JavaScript Object Notation)在网络传输中几乎无处不在，JSON是一种轻量级的数据交换格式，是基于JavaScript（Standard ECMA-262 3rd Edition - December 1999）的一个子集。 JSON采用完全独立于语言的文本格式，数据格式容易阅读和编写，同时也非常便于机器解析和生成，在网络传输速度相对于传统的XML快。JSON的英文官网Http://www.json.org/，具体的格式可看官网，如果你是在看不懂，可以参考本文之前在Android中解析JSON的文章，其中还有关于JSON和XML的对比(Android数据解析-JSON解析)。
JSON数据
一个最简单的JSON数据如下{"Name":"FlyElephant"}，Name是键，FlyElephant是值，用{}包裹；开发的时候经常会遇到客户端与服务端打交道，数据传输基本上都是JSON格式，一般都是服务端提供接口数据，那么我开始的时候没有数据怎么办呢，自己单独搞一个JSON字符串自己解析也可以，不过没什么意思，不过还好国家气象局提供的有接口数据，网上有些早的文章写了多个接口，个人测试只有一个接口还是可以用的。http://m.weather.com.cn/data/101180601.HTML，这个链接老家的天气接口，如果你想知道你老家的天气接口，把html前面的数字编码替换即可，如果想看帝都的天气，链接地址如下:http://m.weather.com.cn/data/101010100.html,下面提供了一份全国的城市编码，方便大家测试:
直辖市
"北京","上海","天津","重庆"
"101010100","101020100","101030100","101040100"
特别行政区
"香港","澳门"
"101320101","101330101"
黑龙江
"哈尔滨","齐齐哈尔","牡丹江","大庆","伊春","双鸭山","鹤岗","鸡西","佳木斯","七台河","黑河","绥化","大兴安岭"
"101050101","101050201","101050301","101050901","101050801","101051301","101051201","101051101","101050401","101051002","101050601","101050501","101050701"
吉林
"长春","延吉","吉林","白山","白城","四平","松原","辽源","大安","通化"
"101060101","101060301","101060201","101060901","101060601","101060401","101060801","101060701","101060603","101060501"
辽宁
"沈阳","大连","葫芦岛","盘锦","本溪","抚顺","铁岭","辽阳","营口","阜新","朝阳","锦州","丹东","鞍山"
"101070101","101070201","101071401","101071301","101070501","101070401","101071101","101071001","101070801","101070901","101071201","101070701","101070601","101070301"
内蒙古
"呼和浩特","呼伦贝尔","锡林浩特","包头","赤峰","海拉尔","乌海","鄂尔多斯","通辽"
"101080101","101081000","101080901","101080201","101080601","101081001","101080301","101080701","101080501"
河北
"石家庄","唐山","张家口","廊坊","邢台","邯郸","沧州","衡水","承德","保定","秦皇岛"
"101090101","101090501","101090301","101090601","101090901","101091001","101090701","101090801","101090402","101090201","101091101"
河南
"郑州","开封","洛阳","平顶山","焦作","鹤壁","新乡","安阳","濮阳","许昌","漯河","三门峡","南阳","商丘","信阳","周口","驻马店"
"101180101","101180801","101180901","101180501","101181101","101181201","101180301","101180201","101181301","101180401","101181501","101181701","101180701","101181001","101180601","101181401","101181601"
山东
"济南","青岛","淄博","威海","曲阜","临沂","烟台","枣庄","聊城","济宁","菏泽","泰安","日照","东营","德州","滨州","莱芜","潍坊"
"101120101","101120201","101120301","101121301","101120710","101120901","101120501","101121401","101121701","101120701","101121001","101120801","101121501","101121201","101120401","101121101","101121601","101120601"
山西
"太原","阳泉","晋城","晋中","临汾","运城","长治","朔州","忻州","大同","吕梁"
"101100101","101100301","101100601","101100401","101100701","101100801","101100501","101100901","101101001","101100201","101101101"
江苏
"南京","苏州","昆山","南通","太仓","吴县","徐州","宜兴","镇江","淮安","常熟","盐城","泰州","无锡","连云港","扬州","常州","宿迁"
"101190101","101190401","101190404","101190501","101190408","101190406","101190801","101190203","101190301","101190901","101190402","101190701","101191201","101190201","101191001","101190601","101191101","101191301"
安徽
"合肥","巢湖","蚌埠","安庆","六安","滁州","马鞍山","阜阳","宣城","铜陵","淮北","芜湖","毫州","宿州","淮南","池州"
"101220101","101221601","101220201","101220601","101221501","101221101","101220501","101220801","101221401","101221301","101221201","101220301","101220901","101220701","101220401","101221701"
陕西
"西安","韩城","安康","汉中","宝鸡","咸阳","榆林","渭南","商洛","铜川","延安"
"101110101","101110510","101110701","101110801","101110901","101110200","101110401","101110501","101110601","101111001","101110300"
宁夏
"银川","固原","中卫","石嘴山","吴忠"
"101170101","101170401","101170501","101170201","101170301"
甘肃
"兰州","白银","庆阳","酒泉","天水","武威","张掖","甘南","临夏","平凉","定西","金昌"
"101160101","101161301","101160401","101160801","101160901","101160501","101160701","101050204","101161101","101160301","101160201","101160601"
青海
"西宁","海北","海西","黄南","果洛","玉树","海东","海南"
"101150101","101150801","101150701","101150301","101150501","101150601","101150201","101150401"
湖北
"武汉","宜昌","黄冈","恩施","荆州","神农架","十堰","咸宁","襄阳","孝感","随州","黄石","荆门","鄂州"
"101200101","101200901","101200501","101201001","101200801","101201201","101201101","101200701","101200201","101200401","101201301","101200601","101201401","101200301"
湖南
"长沙","邵阳","常德","郴州","吉首","株洲","娄底","湘潭","益阳","永州","岳阳","衡阳","怀化","韶山","张家界"
"101250101","101250901","101250601","101250501","101251501","101250301","101250801","101250201","101250701","101251401","101251001","101250401","101251201","101250202","101251101"
浙江
"杭州","湖州","金华","宁波","丽水","绍兴","衢州","嘉兴","台州","舟山","温州"
"101210101","101210201","101210901","101210401","101210801","101210501","101211001","101210301","101210601","101211101","101210701"
江西
"南昌","萍乡","九江","上饶","抚州","吉安","鹰潭","宜春","新余","景德镇","赣州"
"101240101","101240901","101240201","101240301","101240401","101240601","101241101","101240501","101241001","101240801","101240701"
福建
"福州","厦门","龙岩","南平","宁德","莆田","泉州","三明","漳州"
"101230101","101230201","101230701","101230901","101230301","101230401","101230501","101230801","101230601"
贵州
"贵阳","安顺","赤水","遵义","铜仁","六盘水","毕节","凯里","都匀"
"101260101","101260301","101260208","101260201","101260601","101260801","101260701","101260501","101260401"
四川
"成都","泸州","内江","凉山","阿坝","巴中","广元","乐山","绵阳","德阳","攀枝花","雅安","宜宾","自贡","甘孜州","达州","资阳","广安","遂宁","眉山","南充"
"101270101","101271001","101271201","101271601","101271901","101270901","101272101","101271401","101270401","101272001","101270201","101271701","101271101","101270301","101271801","101270601","101271301","101270801","101270701","101271501","101270501"
广东
"广州","深圳","潮州","韶关","湛江","惠州","清远","东莞","江门","茂名","肇庆","汕尾","河源","揭阳","梅州","中山","德庆","阳江","云浮","珠海","汕头","佛山"
"101280101","101280601","101281501","101280201","101281001","101280301","101281301","101281601","101281101","101282001","101280901","101282101","101281201","101281901","101280401","101281701","101280905","101281801","101281401","101280701","101280501","101280800"
广西
"南宁","桂林","阳朔","柳州","梧州","玉林","桂平","贺州","钦州","贵港","防城港","百色","北海","河池","来宾","崇左"
"101300101","101300501","101300510","101300301","101300601","101300901","101300802","101300701","101301101","101300801","101301401","101301001","101301301","101301201","101300401","101300201"
云南
"昆明","保山","楚雄","德宏","红河","临沧","怒江","曲靖","思茅","文山","玉溪","昭通","丽江","大理"
"101290101","101290501","101290801","101291501","101290301","101291101","101291201","101290401","101290901","101290601","101290701","101291001","101291401","101290201"
海南
"海口","三亚","儋州","琼山","通什","文昌"
"101310101","101310201","101310205","101310102","101310222","101310212"
新疆
"乌鲁木齐","阿勒泰","阿克苏","昌吉","哈密","和田","喀什","克拉玛依","石河子","塔城","库尔勒","吐鲁番","伊宁"
"101130101","101131401","101130801","101130401","101131201","101131301","101130901","101130201","101130301","101131101","101130601","101130501","101131001"
西藏
"拉萨","阿里","昌都","那曲","日喀则","山南","林芝"
"101140101","101140701","101140501","101140601","101140201","101140301","101140401"
台湾
"台北","高雄"
"101340102","101340201"
天气返回的数据就是JSON格式，不需要自己提供数据，图片如下:
JSON解析
解析JSON一般有四种方式TouchJson、 SBJson 、JSONKit 和NSJSONSerialization，性能和速度的NSJSONSerialization>JSONKit>SBJSON>TouchJson,NSJSONSerialization是iOS5之后系统提供的，其他的为第三方类库，现在手机基本上都是iOS6以上，本文就从系统自带的NSJSONSerialization来解析JSON数据。
NSJSONSerialization有两个方法:
dataWithJSONObject:从OC对象转换成JSON数据
JSONObjectWithData:从JSON转成OC对象
/* Generate JSON data from a foundation object. If the object will not produce valid JSON then an exception will be thrown. Setting the NSJSONWritingPrettyPrinted option will generate JSON with whitespace designed to make the output more readable. If that option is not set, the most compact possible JSON will be generated. If an error occurs, the error parameter will be set and the return value will be nil. The resulting data is a encoded in UTF-8. */ + (NSData *)dataWithJSONObject:(id)obj options:(NSJSONWritingOptions)opt error:(NSError **)error; /* Create a Foundation object from JSON data. Set the NSJSONReadingAllowFragments option if the parser should allow top-level objects that are not an NSArray or NSDictionary. Setting the NSJSONReadingMutableContainers option will make the parser generate mutable NSArrays and NSDictionaries. Setting the NSJSONReadingMutableLeaves option will make the parser generate mutable NSString objects. If an error occurs during the parse, then the error parameter will be set and the result will be nil. The data must be in one of the 5 supported encodings listed in the JSON specification: UTF-8, UTF-16LE, UTF-16BE, UTF-32LE, UTF-32BE. The data may or may not have a BOM. The most efficient encoding to use for parsing is UTF-8, so if you have a choice in encoding the data passed to this method, use UTF-8. */ + (id)JSONObjectWithData:(NSData *)data options:(NSJSONReadingOptions)opt error:(NSError **)error;
故事板中放置一个UITextView:
@property (weak, nonatomic) IBOutlet UITextView *myTextView;
viewDidLoad中代码:
//设置URL
NSURL *url=[NSURL URLWithString:@"http://m.weather.com.cn/data/101180601.html"];
//设置请求
NSURLRequest *request=[NSURLRequest requestWithURL:url];
//接收数据
NSData *responseData=[NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
//解析数据
NSDictionary *weatherDic = [NSJSONSerialization JSONObjectWithData:responseData options:NSJSONReadingMutableLeaves error:nil];
//展示结果
NSDictionary *weatherResult= [weatherDic objectForKey:@"weatherinfo"];
self.myTextView.text= [NSString stringWithFormat:@"今天是 %@ %@ %@ 的天气状况：温度%@ %@ %@---FlyElephant:http://www.cnblogs.com/xiaofeixiang",[weatherResult objectForKey:@"date_y"],[weatherResult objectForKey:@"week"],[weatherResult objectForKey:@"city"], [weatherResult objectForKey:@"temp1"],[weatherResult objectForKey:@"weather1"],[weatherResult objectForKey:@"index_ls"]];
跟之前的网络请求一样，代码中有解析，如果不明白可以参考之前文章，最终演示效果如下:
