WP学习笔记（3）wp解析json

接着上一篇，在上一篇里我们通过http请求获得了北京的天气预报，但是返回格式是json，在做web的时候肯定对json再熟悉不过了，今天就看看怎么在windows phone8里解析json。在wp里本身就集成了解析json的类System.Runtime.Serialization.Json.DataContractJsonSerializer。除此之外还可以用第三方开源类库json.net。下面是我在json.net的home上看到的（见文章最后备注）,从这个数据来看无论是支持的功能还是序列化和反序列化的性能，都是json.net好，但是这个数据本身就是json.net提供的，不做评论。

上次我们从http://www.weather.com.cn/data/cityinfo/101010100.html获取到的天气数据是这样的

{"weatherinfo":{"city":"北京","cityid":"101010100","temp1":"27℃","temp2":"22℃","weather":"大雨转中雨","img1":"d9.gif","img2":"n8.gif","ptime":"11:00"}}

我们先不管这些都是什么内容，只观察这个json的格式，创建的实体类应该是这样的

public class WeatherModel
    {
        public WeatherInforDetails weatherinfo { get; set; }
        public class WeatherInforDetails
        {
            public string city { get; set; }
            public string cityid { get; set; }
            public string temp1 { get; set; }
            public string temp2 { get; set; }
            public string weather { get; set; }
            public string img1 { get; set; }
            public string img2 { get; set; }
            public string ptime { get; set; }
        }
    }

再把上一篇里的请求扩展下，先看看用.net自带的DataContractJsonSerializer要怎么写

HttpClient hc = new HttpClient();
try
{
   var task = await hc.GetAsync("http://www.weather.com.cn/data/cityinfo/101010100.html");
   string result = await task.Content.ReadAsStringAsync();
   using (MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes(result)))
   {
       WeatherModel obj = Activator.CreateInstance<WeatherModel>();
       DataContractJsonSerializer js = new DataContractJsonSerializer(obj.GetType());
       WeatherModel model = (WeatherModel)js.ReadObject(ms);
       MessageBox.Show(model.weatherinfo.city); 
   }
                
}
catch (Exception e)
{
   MessageBox.Show(e.Message);
}

调试一下，已经可以出结果了。我们再看看用json.net应该怎么做，其他地方不用动，只要把上面try里的代码换一下就行

在调整调整之前要先下载json.net的dll，可以从这里下载http://json.codeplex.com/，注意在wp项目中引用dll的时候要引用Portable40文件夹下的Newtonsoft.Json.dll

WeatherModel model = (WeatherModel)JsonConvert.DeserializeObject(result, typeof(WeatherModel));
MessageBox.Show(model.weatherinfo.city);

调试一下也没问题，json.net稍微简洁了一点。看下面的对比表格，json.net支持linq to json，我们再看看如何用json.net的linq to json。

JObject obj = JObject.Parse(result);
JToken tok = obj["weatherinfo"];
MessageBox.Show(tok["city"].ToString());

居然还可以这么用，而且JObject还可以用foreach遍历，可以转换成array，list，collection等等。
看到这突然灵光一线，对于这个json来说只是嵌套了一层，对于从另外一个更全的可以获得未来5天的天气api来说，返回的json简直就太复杂了，而且很多数据我们并用到，时不时可以用这样的写法简化一下model呢。我们再建一个model，WeatherModel1

public class WeatherModel1
    {
        public string city { get; set; }
        public string cityid { get; set; }
        public string temp1 { get; set; }
        public string temp2 { get; set; }
        public string weather { get; set; }
        public string img1 { get; set; }
        public string img2 { get; set; }
        public string ptime { get; set; }
    }

再把解析json的地方改成这样

 JObject obj = JObject.Parse(result);
WeatherModel1 details = (WeatherModel1)JsonConvert.DeserializeObject(obj["weatherinfo"].ToString(), typeof(WeatherModel1));
MessageBox.Show(details.city);

是不是简单了不少，对于那些返回数据比较发杂的的json数据来说就太有用了。

备注：

	Json.NET	DataContractJsonSerializer	JavaScriptSerializer
Supports JSON
Supports BSON
Supports JSON Schema
Supports .NET 2.0
Supports .NET 3.5
Supports .NET 4.0
Supports .NET 4.5
Supports Silverlight
Supports Windows Phone
Supports Windows 8
Supports Portable Class Library
Open Source
MIT License
LINQ to JSON
Thread Safe
XPath-like JSON query syntax
Indented JSON support
Efficient dictionary serialization
Nonsensical dictionary serialization
Deserializes IList, IEnumerable, ICollection, IDictionary properties
Serializes circular references
Supports serializing objects by reference
Deserializes polymorphic properties and collections
Serializes and deserializes multidimensional arrays
Supports including type names with JSON
Globally customize serialization process
Supports excluding null values when serializing
Supports SerializationBinder
Conditional property serialization
Includes line number information in errors
Converts XML to JSON and JSON to XML
JSON Schema validation
JSON Schema generation from .NET types
Camel case JSON property names
Non-default constructors support
Serialization error handling
Supports populating an existing object
Efficiently serializes byte arrays as base64 text
Handles NaN, Infinity, -Infinity and undefined
Handles JavaScript constructors
Serializes .NET 4.0 dynamic objects
Serializes ISerializable objects
Supports serializing enums to their text name
JSON recursion limit support
Attribute property name customization
Attribute property order customization
Attribute property required customization
Supports ISO8601 dates
Supports JavaScript constructor dates
Supports Microsoft AJAX dates
Unquoted property names support
Raw JSON support
Supports reading and writing comments
Supports BigInteger
Serializes anonymous types
Deserializes anonymous types
Deserializes read only collections
Opt-in mode serialization
Opt-out mode serialization
Field (Serializable) mode serialization
Efficiently stream reading and writing JSON
Single or double quote JSON content
Supports overriding a type's serialization
Supports OnDeserialized, OnSerializing, OnSerialized and OnDeserializing attributes
Supports serializing private properties
DataMember attribute support
MetdataType attribute support
DefaultValue attribute support
Serializes DataSets and DataTables
Serailizes Entity Framework
Serializes nHibernate
Case-insensitive property deserialization
Tracing