XML Serialize generic list of serializable objects

Question

Can I serialize a generic list of serializable objects without having to specify their type   Something like the intention behind the broken code below   List lt ISerializable gt  serializableList   new List lt ISerializable gt      XmlSerializer xmlSerializer   new XmlSerializer serializableList GetType      serializableList Add  ISerializable PersonList    using  StreamWriter streamWriter   System IO File CreateText fileName         xmlSerializer Serialize streamWriter  serializableList       Edit   For those who wanted to know detail  when I try to run this code  it errors on the XMLSerializer      line with   Cannot serialize interface System Runtime Serialization ISerializable   If I change to List lt object gt  I get  There was an error generating the XML document    The InnerException detail is    The type System Collections Generic List1  Project1 Person  ConsoleFramework  Version 1 0 0 0  Culture neutral  PublicKeyToken null   may not be used in this context      The person object is defined as follows    XmlRoot  Person    public class Person       string  firstName   String Empty      string  lastName   String Empty       private Person                    public Person string lastName  string firstName                 lastName   lastName           firstName   firstName              XmlAttribute DataType    string   AttributeName    LastName        public string LastName               get   return  lastName            set    lastName   value                XmlAttribute DataType    string   AttributeName    FirstName        public string FirstName               get   return  firstName            set    firstName   value              The PersonList is just a List lt Person gt     This is just for testing though  so didn t feel the details were too important  The key is I have one or more different objects  all of which are serializable  I want to serialize them all to one file  I thought the easiest way to do that would be to put them in a generic list and serialize the list in one go  But this doesn t work   I tried with List lt IXmlSerializable gt  as well  but that fails with  System Xml Serialization IXmlSerializable cannot be serialized because it does not have a parameterless constructor   Sorry for the lack of detail  but I am a beginner at this and don t know what detail is required  It would be helpful if people asking for more detail tried to respond in a way that would leave me understanding what details are required  or a basic answer outlining possible directions   Also thanks to the two answers I ve got so far - I could have spent a lot more time reading without getting these ideas  It s amazing how helpful people are on this site

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The easiest way to do it  that I have found    Apply the System Xml Serialization XmlArray attribute to it    System Xml Serialization XmlArray    This is the part that makes it work List lt object gt  serializableList   new List lt object gt      XmlSerializer xmlSerializer   new XmlSerializer serializableList GetType      serializableList Add PersonList    using  StreamWriter streamWriter   System IO File CreateText fileName         xmlSerializer Serialize streamWriter  serializableList       The serializer will pick up on it being an array and serialize the list s items as child nodes

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I think Dreas  approach is ok  An alternative to this however is to have some static helper methods and implement IXmlSerializable on each of your methods e g an XmlWriter extension method and the XmlReader one to read it back   public static void SaveXmlSerialiableElement lt T gt  this XmlWriter writer  String elementName  T element  where T   IXmlSerializable      writer WriteStartElement elementName      writer WriteAttributeString  TYPE   element GetType   AssemblyQualifiedName      element WriteXml writer      writer WriteEndElement       public static T ReadXmlSerializableElement lt T gt  this XmlReader reader  String elementName  where T   IXmlSerializable      reader ReadToElement elementName       Type elementType   Type GetType reader GetAttribute  TYPE        T element    T Activator CreateInstance elementType      element ReadXml reader      return element      If you do go down the route of using the XmlSerializer class directly  create serialization assemblies before hand if possible  as you can take a large performance hit in constructing new XmlSerializers regularly   For a collection you need something like this   public static void SaveXmlSerialiazbleCollection lt T gt  this XmlWriter writer  String collectionName  String elementName  IEnumerable lt T gt  items  where T   IXmlSerializable      writer WriteStartElement collectionName      foreach  T item in items             writer WriteStartElement elementName         writer WriteAttributeString  TYPE   item GetType   AssemblyQualifiedName         item WriteXml writer         writer WriteEndElement            writer WriteEndElement

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I think it s best if you use methods with generic arguments  like the following    public static void SerializeToXml lt T gt  T obj  string fileName        using  var fileStream   new FileStream fileName  FileMode Create                  var ser   new XmlSerializer typeof T             ser Serialize fileStream  obj            public static T DeserializeFromXml lt T gt  string xml        T result      var ser   new XmlSerializer typeof T        using  var tr   new StringReader xml                 result    T ser Deserialize tr             return result

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See Introducing XML Serialization   Items That Can Be Serialized The following items can be serialized using the XmlSerializer class   Public read write properties and fields of public classes Classes that implement ICollection or IEnumerable XmlElement objects XmlNode objects DataSet objects    In particular  ISerializable or the  Serializable  attribute does not matter   Now that you ve told us what your problem is   quot it doesn t work quot  is not a problem statement   you can get answers to your actual problem  instead of guesses  When you serialize a collection of a type  but will actually be serializing a collection of instances of derived types  you need to let the serializer know which types you will actually be serializing  This is also true for collections of object  You need to use the XmlSerializer Type Type    constructor to give the list of possible types

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Below is a Util class  in my project   namespace Utils       public static class SerializeUtil               public static void SerializeToFormatter lt F gt  object obj  string path  where F   IFormatter  new                         if  obj    null                                throw new NullReferenceException  obj Cannot be Null                                if  obj GetType   IsSerializable    false                                    throw new                            IFormatter f   new F                SerializeToFormatter obj  path  f                      public static T DeserializeFromFormatter lt T  F gt  string path  where F   IFormatter  new                         T t              IFormatter f   new F                using  FileStream fs   File OpenRead path                                 t    T f Deserialize fs                             return t                     public static void SerializeToXML lt T gt  string path  object obj                        XmlSerializer xs   new XmlSerializer typeof T                using  FileStream fs   File Create path                                 xs Serialize fs  obj                                    public static T DeserializeFromXML lt T gt  string path                        XmlSerializer xs   new XmlSerializer typeof T                using  FileStream fs   File OpenRead path                                 return  T xs Deserialize fs                                    public static T DeserializeFromXml lt T gt  string xml                        T result               var ser   new XmlSerializer typeof T                using  var tr   new StringReader xml                                 result    T ser Deserialize tr                             return result                      private static void SerializeToFormatter object obj  string path  IFormatter formatter                        using  FileStream fs   File Create path                                 formatter Serialize fs  obj

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knowTypeList parameter let serialize with DataContractSerializer several known types   private static void WriteObject          string fileName  IEnumerable lt Vehichle gt  reflectedInstances  List lt Type gt  knownTypeList                using  FileStream writer   new FileStream fileName  FileMode Append                         foreach  var item in reflectedInstances                                var serializer   new DataContractSerializer typeof Vehichle   knownTypeList                   serializer WriteObject writer  item

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You can t serialize a collection of objects without specifying the expected types  You must pass the list of expected types to the constructor of XmlSerializer  the extraTypes parameter     List lt object gt  list   new List lt object gt     list Add new Foo     list Add new Bar      XmlSerializer xs   new XmlSerializer typeof object   new Type    typeof Foo   typeof Bar     using  StreamWriter streamWriter   System IO File CreateText fileName         xs Serialize streamWriter  list       If all the objects of your list inherit from the same class  you can also use the XmlInclude attribute to specify the expected types     XmlInclude typeof Foo    XmlInclude typeof Bar    public class MyBaseClass

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I have an solution for a generic List lt   with dynamic binded items   class PersonalList it s the root element   XmlRoot  PersonenListe     XmlInclude typeof Person       include type class Person public class PersonalList        XmlArray  PersonenArray         XmlArrayItem  PersonObjekt        public List lt Person gt  Persons   new List lt Person gt           XmlElement  Listname        public string Listname   get  set            Konstruktoren      public PersonalList            public PersonalList string name                this Listname   name             public void AddPerson Person person                Persons Add person             class Person it s an single list element    XmlType  Person       define Type  XmlInclude typeof SpecialPerson    XmlInclude typeof SuperPerson                 include type class SpecialPerson and class SuperPerson public class Person        XmlAttribute  PersID   DataType    string        public string ID   get  set          XmlElement  Name        public string Name   get  set          XmlElement  City        public string City   get  set          XmlElement  Age        public int Age   get  set            Konstruktoren      public Person            public Person string name  string city  int age  string id                this Name   name          this City   city          this Age   age          this ID   id            class SpecialPerson inherits Person   XmlType  SpecialPerson       define Type public class SpecialPerson   Person        XmlElement  SpecialInterests        public string Interests   get  set         public SpecialPerson            public SpecialPerson string name  string city  int age  string id  string interests                this Name   name          this City   city          this Age   age          this ID   id          this Interests   interests            class SuperPerson inherits Person   XmlType  SuperPerson       define Type public class SuperPerson   Person        XmlArray  Skills         XmlArrayItem  Skill        public List lt String gt  Skills   get  set          XmlElement  Alias        public string Alias   get  set         public SuperPerson                  Skills   new List lt String gt                public SuperPerson string name  string city  int age  string id  string   skills  string alias                Skills   new List lt String gt              this Name   name          this City   city          this Age   age          this ID   id          foreach  string item in skills                        this Skills Add item                        this Alias   alias            and the main test Source  static void Main string   args        PersonalList personen   new PersonalList         personen Listname    Friends           normal person     Person normPerson   new Person        normPerson ID    0       normPerson Name    Max Man       normPerson City    Capitol City       normPerson Age   33          special person     SpecialPerson specPerson   new SpecialPerson        specPerson ID    1       specPerson Name    Albert Einstein       specPerson City    Ulm       specPerson Age   36      specPerson Interests    Physics           super person     SuperPerson supPerson   new SuperPerson        supPerson ID    2       supPerson Name    Superman       supPerson Alias    Clark Kent       supPerson City    Metropolis       supPerson Age   int MaxValue      supPerson Skills Add  fly        supPerson Skills Add  strong            Add Persons     personen AddPerson normPerson       personen AddPerson specPerson       personen AddPerson supPerson           Serialize      Type   personTypes     typeof Person   typeof SpecialPerson   typeof SuperPerson         XmlSerializer serializer   new XmlSerializer typeof PersonalList   personTypes        FileStream fs   new FileStream  Personenliste xml   FileMode Create        serializer Serialize fs  personen        fs Close         personen   null          Deserialize      fs   new FileStream  Personenliste xml   FileMode Open        personen    PersonalList serializer Deserialize fs        serializer Serialize Console Out  personen       Console ReadLine        Important is the definition and includes of the diffrent types

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If the XML output requirement can be changed you can always use binary serialization - which is better suited for working with heterogeneous lists of objects  Here s an example   private void SerializeList List lt Object gt  Targets  string TargetPath        IFormatter Formatter   new BinaryFormatter         using  FileStream OutputStream   System IO File Create TargetPath                 try                       Formatter Serialize OutputStream  Targets             catch  SerializationException ex                   Likely Failed to Mark Type as Serializable                                  Use as such        Serializable  public class Animal       public string Home   get  set        Serializable  public class Person       public string Name   get  set        public void ExampleUsage          List lt Object gt  SerializeMeBaby   new List lt Object gt            new Animal   Home    London  UK             new Person   Name    Skittles                string TargetPath   Path Combine          Environment GetFolderPath Environment SpecialFolder ApplicationData            Test1 dat         SerializeList SerializeMeBaby  TargetPath

[c#] XML Serialize generic list of serializable objects

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