[英]How can I deserialize JSON when the object type is not known beforehand?
[英]How do I use an XmlSerializer to deserialize an object that might be of a base or derived class without knowing the type beforehand?
在C#中,如何使用XmlSerializer
反序列化可能是基類的對象,或者在不事先知道類型的情況下反序列化任何幾個派生類?
我的所有派生類都添加了其他數據成員。 我已經制作了一個簡單的GUI,可以序列化和反序列化類對象。 它將序列化對象,因為任何繼承的類(甚至只是基類)都適合於用戶選擇填充的字段。
我對序列化沒有任何問題; 問題是反序列化。 如何在不事先知道類的情況下讓XmlSerializer
將數據反序列化為正確的派生類? 我目前創建一個XmlReader
來讀取XML文件的第一個節點並從中確定類,它似乎適用於我的目的,但它似乎是一個非常不優雅的解決方案。
我在下面發布了一些示例代碼。 有什么建議么?
BaseType objectOfConcern = new BaseType();
XmlSerializer xserializer;
XmlTextReader xtextreader = new XmlTextReader(DEFAULT_FILENAME);
do { xtextreader.Read(); } while (xtextreader.NodeType != XmlNodeType.Element);
string objectType = xtextreader.Name;
xtextreader.Close();
FileStream fstream = new FileStream(DEFAULT_FILENAME, FileMode.Open);
switch (objectType)
{
case "type1":
xserializer = new XmlSerializer(typeof(DerivedType));
objectOfConcern = (DerivedType)xserializer.Deserialize(fstream);
//Load fields specific to that derived type here
whatever = (objectOfConcern as DerivedType).NoOfstreamubordinates.ToString();
case "xxx_1":
//code here
case "xxx_2":
//code here
case "xxx_n":
//code here
//and so forth
case "BaseType":
xserializer = new XmlSerializer(typeof(BaseType));
AssignEventHandler(xserializer);
objectOfConcern = (BaseType)xserializer.Deserialize(fstream);
}
//Assign all deserialized values from base class common to all derived classes here
//Close the FileStream
fstream.Close();
你有一些包含派生類型的根類/標簽嗎? 如果是,您可以使用XmlElementAttribute將標記名稱映射到類型:
public class RootElementClass
{
[XmlElement(ElementName = "Derived1", Type = typeof(Derived1BaseType))]
[XmlElement(ElementName = "Derived2", Type = typeof(Derived2BaseType))]
[XmlElement(ElementName = "Derived3", Type = typeof(Derived3BaseType))]
public BaseType MyProperty { get; set; }
}
public class BaseType { }
public class Derived1BaseType : BaseType { }
public class Derived2BaseType : BaseType { }
public class Derived3BaseType : BaseType { }
我最近為基類T和T的任何派生類編寫了這個通用的serializer \\ deserializer。到目前為止似乎工作。
Type []數組存儲T和T本身的所有派生類型。 反序列化器會嘗試每一個,並在找到正確的序列時返回。
/// <summary>
/// A generic serializer\deserializer
/// </summary>
/// <typeparam name="T"></typeparam>
public static class Serializer<T>
{
/// <summary>
/// serialize an instance to xml
/// </summary>
/// <param name="instance"> instance to serialize </param>
/// <returns> instance as xml string </returns>
public static string Serialize(T instance)
{
StringBuilder sb = new StringBuilder();
XmlWriterSettings settings = new XmlWriterSettings();
using (XmlWriter writer = XmlWriter.Create(sb, settings))
{
XmlSerializer serializer = new XmlSerializer(instance.GetType());
serializer.Serialize(writer, instance);
}
return sb.ToString();
}
/// <summary>
/// deserialize an xml into an instance
/// </summary>
/// <param name="xml"> xml string </param>
/// <returns> instance </returns>
public static T Deserialize(string xml)
{
using (XmlReader reader = XmlReader.Create(new StringReader(xml)))
{
foreach (Type t in types)
{
XmlSerializer serializer = new XmlSerializer(t);
if (serializer.CanDeserialize(reader))
return (T)serializer.Deserialize(reader);
}
}
return default(T);
}
/// <summary>
/// store all derived types of T:
/// is used in deserialization
/// </summary>
private static Type[] types = AppDomain.CurrentDomain.GetAssemblies()
.SelectMany(s => s.GetTypes())
.Where(t => typeof(T).IsAssignableFrom(t)
&& t.IsClass
&& !t.IsGenericType)
.ToArray();
}
您可以嘗試使用構造函數XmlSerializer(Type type,Type [] extraTypes)來創建一個適用於所有相關類型的序列化程序。
如果您未設置使用XmlSerializer
,則可以使用帶有KnownType
屬性的DataContractSerializer
。
您需要做的就是為每個子類的父類添加一個KnownType
屬性, DataContractSerializer
將完成剩下的工作。
在序列化為xml時, DataContractSerializer
將添加類型信息,並在反序列化時使用該類型信息來創建正確的類型。
例如,以下代碼:
[KnownType( typeof( C2 ) )]
[KnownType( typeof( C3 ) )]
public class C1 {public string P1 {get;set;}}
public class C2 :C1 {public string P2 {get;set;}}
public class C3 :C1 {public string P3 {get;set;}}
class Program
{
static void Main(string[] args)
{
var c1 = new C1{ P1="c1"};
var c2 = new C2{ P1="c1", P2="c2"};
var c3 = new C3{ P1="c1", P3="c3"};
var s = new DataContractSerializer( typeof( C1 ) );
Test( c1, s );
Test( c2, s );
Test( c3, s );
}
static void Test( C1 objectToSerialize, DataContractSerializer serializer )
{
using ( var stream = new MemoryStream() )
{
serializer.WriteObject( stream, objectToSerialize );
stream.WriteTo( Console.OpenStandardOutput() );
stream.Position = 0;
var deserialized = serializer.ReadObject( stream );
Console.WriteLine( Environment.NewLine + "Deserialized Type: " + deserialized.GetType().FullName );
}
}
}
將輸出:
<C1 xmlns="http://schemas.datacontract.org/2004/07/ConsoleApplication1" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
<P1>c1</P1></C1>
Deserialized Type: ConsoleApplication1.C1
<C1 i:type="C2" xmlns="http://schemas.datacontract.org/2004/07/ConsoleApplication1" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
<P1>c1</P1><P2>c2</P2></C1>
Deserialized Type: ConsoleApplication1.C2
<C1 i:type="C3" xmlns="http://schemas.datacontract.org/2004/07/ConsoleApplication1" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
<P1>c1</P1><P3>c3</P3></C1>
Deserialized Type: ConsoleApplication1.C3
在輸出中,您會注意到c2和c3的xml包含額外的類型信息,這些信息允許DataContractSerializer.ReadObject
創建正確的類型。
你可以使用XmlInclude
[XmlInclude(typeof(MyClass))]
public abstract class MyBaseClass
{
//...
}
否則,如果要在序列化時添加類型:
Type[] types = new Type[]{ typeof(MyClass) }
XmlSerializer serializer = new XmlSerializer(typeof(MyBaseClass), types);
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