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Is it possible to create a ConfigurationElement from xml text?

We have a custom class that inherits from ConfigurationElement called SignalConfigurationElement and defines a bunch of properties using the ConfigurationProperty attribute.
The SignalConfigurationElement class is part of a much larger hierarchy of configuration elements and does not have a constructor. I'm able to retrieve the entire configuration through the ConfigurationManager.GetSection() call, providing the root element's name which is SystemConfiguration, which is defined in the <configSections> of the app.config file.
I don't have control over the custom configuration elements so I can't alter them to provide constructors. I also can't modify the app.config because it's used by a much larger application.
Is it possible to create instances or collections of SignalConfigurationElement given an XML string of <signals> entries? The class doesn't have a constructor so I'm assuming the ConfigurationManager.GetSection call used by our other applications to retrieve the entire configuration (not what I want) uses reflection to create its instances.
Code (Can't change any of this at all.):
App.Config
<configSections>
<section name="SystemConfiguration" type="Fully.Qualified.Namespace.SystemConfiguration, SystemConfiguration"/>
</configSections>
<SystemConfiguration id="System1" name="System 1">
<equipments>
<clear />
<add id="Equipment11" equipmentType="EQ">
<signals>
<clear />
<add id="EQ11Signal1" signalId="EQ11Signal1" type="Version" />
<add id="EQ11Signal2" signalId="EQ11Signal2" type="Status" />
<add id="EQ11Signal3" signalId="EQ11Signal3" type="Status" />
</signals>
</add>
<add id="Equipment21" equipmentType="EQ">
<signals>
<clear />
<add id="EQ21Signal1" signalId="EQ21Signal1" type="Version" />
<add id="EQ21Signal2" signalId="EQ21Signal2" type="Status" />
<add id="EQ21Signal3" signalId="EQ21Signal3" type="Status" />
</signals>
</add>
</equipments>
<!-- And a whole lot more. Somewhere in the avenue of 30,000 <signals> entries.-->
</SystemConfiguration>
Classes:
public class SystemConfigurationSection : ConfigurationSection
{
/// <summary>
/// Determines the XML tag that will contain this Configuration Section in an .config file.
/// </summary>
public const string SystemConfigurationSectionName = "SystemConfiguration";
/// <summary>
/// Instance factory method for an instance of the Configuration Section creation.
/// </summary>
/// <returns>
/// Instance of the System Configuration section created based on the .config file of the application.
/// </returns>
public static SystemConfigurationSection GetSystemConfigurationSection()
{
SystemConfigurationSection result =
(SystemConfigurationSection) ConfigurationManager.GetSection(SystemConfigurationSectionName);
return result;
}
/// <summary>
/// Represents the XML attribute used to store ID of the System.
/// </summary>
[ConfigurationProperty(IdConfigurationElementName, IsRequired = true)]
public string Id
{
get { return (string) this[IdConfigurationElementName]; }
set { this[IdConfigurationElementName] = value; }
}
/// <summary>
/// Determines name of the XML attribute that will contain ID of the System.
/// </summary>
public const string IdConfigurationElementName = "id";
/// <summary>
/// Represents the XML attribute used to store Name of the System.
/// </summary>
[ConfigurationProperty(NameConfigurationElementName, IsRequired = true)]
public string Name
{
get { return (string) this[NameConfigurationElementName]; }
set { this[NameConfigurationElementName] = value; }
}
/// <summary>
/// Determines name of the XML attribute that will contain Name of the System.
/// </summary>
public const string NameConfigurationElementName = "name";
/// <summary>
/// Represents the XML attribute used to store Description of the System
/// </summary>
[ConfigurationProperty(DescriptionConfigurationElementName, IsRequired = false, DefaultValue = "")]
public string Description
{
get { return (string) this[DescriptionConfigurationElementName]; }
set { this[DescriptionConfigurationElementName] = value; }
}
/// <summary>
/// Determines name of the XML attribute that will contain Name of the System.
/// </summary>
public const string DescriptionConfigurationElementName = "description";
/// <summary>
/// Represents the collection of the System's Equipments as they are described in the .config file.
/// </summary>
[ConfigurationProperty(EquipmentsConfigurationElementCollectionName, IsDefaultCollection = false)]
[ConfigurationCollection(typeof (EquipmentConfigurationElementCollection), AddItemName = "add",
ClearItemsName = "clear", RemoveItemName = "remove")]
public EquipmentConfigurationElementCollection Equipments
{
get { return (EquipmentConfigurationElementCollection) base[EquipmentsConfigurationElementCollectionName]; }
}
/// <summary>
/// Determines name of the XML tag that will contain collection of the System's Equipments.
/// </summary>
public const string EquipmentsConfigurationElementCollectionName = "equipments";
}
/// <summary>
/// Extends the standard .Net ConfigurationElementCollection re-definind commectio manipulation members and making them strongly-typed.
/// </summary>
/// <typeparam name="TElementType">Type of the Configuration Elements that can be included into the collection.</typeparam>
public class ConfigurationElementCollectionBase<TElementType> : ConfigurationElementCollection, IEnumerable<TElementType>
where TElementType : ConfigurationElement, new()
{
/// <summary>
/// Makes the addition operation public.
/// </summary>
/// <param name="customElement">Configuration element to add to the collection.</param>
public virtual void Add(TElementType customElement)
{
BaseAdd(customElement);
}
/// <summary>
/// Overrides the base implementation of the overloaded method masking an exception throwing.
/// </summary>
/// <param name="element">Configuration element to add.</param>
protected override void BaseAdd(ConfigurationElement element)
{
BaseAdd(element, false);
}
/// <summary>
/// Overrides the base property hardcoding the returned value.
/// </summary>
public override ConfigurationElementCollectionType CollectionType
{
get { return ConfigurationElementCollectionType.AddRemoveClearMap; }
}
/// <summary>
/// Overrides the base implementation of the instance factory method.
/// </summary>
/// <returns>A new instance of the Configuration Element type determined by the type parameter.</returns>
protected override ConfigurationElement CreateNewElement()
{
return new TElementType();
}
/// <summary>
/// Overrides the base implementation of the method determining the indexing algorithm used in the collection.
/// </summary>
/// <param name="element">The configuration element to get index of.</param>
/// <returns></returns>
protected override object GetElementKey(ConfigurationElement element)
{
return ((TElementType)element);
}
/// <summary>
/// Collection's element accessor by index property.
/// </summary>
/// <param name="index">Index of the desired element in the collection.</param>
/// <returns>The requested collection element if exists.</returns>
public TElementType this[int index]
{
get { return (TElementType)BaseGet(index); }
set
{
if (BaseGet(index) != null)
{
BaseRemoveAt(index);
}
BaseAdd(index, value);
}
}
/// <summary>
/// Overrides the collection's element accessor by key property.
/// </summary>
/// <param name="id">Key of the desired collection element.</param>
/// <returns>The requested collection element if exists</returns>
public new TElementType this[string id]
{
get { return (TElementType)BaseGet(id); }
}
/// <summary>
/// Implements a standard collection method looking for an element in the collection and returning the element's index if found.
/// </summary>
/// <param name="element">The element to look for.</param>
/// <returns>Index of the element in the collection if exists.</returns>
public int GetIndexOf(TElementType element)
{
return BaseIndexOf(element);
}
/// <summary>
/// Implements a standard collection method removing an element from the collection.
/// </summary>
/// <param name="url">The element to be removed from the collection.</param>
public void Remove(TElementType url)
{
if (BaseIndexOf(url) >= 0)
BaseRemove(url);
}
/// <summary>
/// Implements the standard collection member removing an element from the collection by the element's index.
/// </summary>
/// <param name="index">Index of the element to be removed from the collection.</param>
public void RemoveAt(int index)
{
BaseRemoveAt(index);
}
/// <summary>
/// Implements a standard collection method removing an element by the element's key.
/// </summary>
/// <param name="id">Key of the element to be removed from the collection.</param>
public void Remove(string id)
{
BaseRemove(id);
}
/// <summary>
/// Implements the standard collection method that clears the collection.
/// </summary>
public void Clear()
{
BaseClear();
}
public new IEnumerator<TElementType> GetEnumerator()
{
for (int i = 0; i < Count; i++)
{
yield return this[i];
}
}
public class EquipmentConfigurationElement : ConfigurationElement
{
/// <summary>
/// Represents the collection of the Equipment Unit's Signals as they are described in the .config file.
/// </summary>
[ConfigurationProperty(signalsConfigurationElementCollectionName, IsDefaultCollection = false)]
[ConfigurationCollection(typeof(SignalConfigurationElementCollection), AddItemName = "add", ClearItemsName = "clear", RemoveItemName = "remove")]
public SignalConfigurationElementCollection Signals
{
get
{
return (SignalConfigurationElementCollection)base[signalsConfigurationElementCollectionName];
}
}
/// <summary>
/// Determines name of the XML tag that will contain collection of the Equipment Unit's Signals.
/// </summary>
private const string signalsConfigurationElementCollectionName = "signals";
}
/// <summary>
/// Represents a type-safe collection of Equipment Unit Configuration Elements.
/// </summary>
public class EquipmentConfigurationElementCollection : ConfigurationElementCollectionBase<EquipmentConfigurationElement>
{
}
/// <summary>
/// Represensts a Signal's configuration element
/// </summary>
/// <remarks>
/// As the class is derived from ConfigurationElementBase, a Signal's configuration element will expect "is", "name", and "description" XML attributes defined in the configuration file.
/// </remarks>
public sealed class SignalConfigurationElement : ConfigurationElement
{
/// <summary>
/// Represents an XML attribute used to determine type of the Signal.
/// </summary>
/// <remarks>
/// The attribute is expected to have a string value which is equal to one of SignalType enumeration member names: "Status" or "Command".
/// </remarks>
[ConfigurationProperty(typeConfigurationElementName, IsRequired = false, DefaultValue = "status")]
public string Type
{
get { return (string) this[typeConfigurationElementName]; }
set { this[typeConfigurationElementName] = value; }
}
/// <summary>
/// Determines name of the XML attribute that will contain type of the Signal.
/// </summary>
private const string typeConfigurationElementName = "type";
}
/// <summary>
/// Represents a type-safe collection of Signal Configuration Elements.
/// </summary>
public class SignalConfigurationElementCollection : ConfigurationElementCollectionBase<SignalConfigurationElement>
{
}

This is possible through the dark arts of reflection. Given the XML shown in your question, you can do this:
var configXml = GetAppConfigXml(); // Returns the XML shown in your question.
var config = (SystemConfigurationSection)Activator.CreateInstance(typeof(SystemConfigurationSection), true);
using (var sr = new StringReader(configXml))
using (var xmlReader = XmlReader.Create(sr))
{
if (xmlReader.ReadToDescendant("SystemConfiguration"))
using (var subReader = xmlReader.ReadSubtree())
{
var dynMethod = config.GetType().GetMethod("DeserializeSection", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public, null, new[] { typeof(XmlReader) }, null);
dynMethod.Invoke(config, new object[] { subReader });
}
}
Debug.Assert(config.Equipments.Count == 2); // No assert
Reference: source for ConfigurationSection.DeserializeSection.
Incidentally, the configuration classes attached to your question don't match the XML. Some properties are missing, and the properties that correspond to attributes in the XML must have IsKey = true. If the XML doesn't match the configuration classes, DeserializeSection will throw an exception.

Nullable Types as Generics

I'm trying to create a linked list for my personal library that can handle EVERYTHING. I'm trying to write it so that it can 'equally' easily hand int, null,DateTime or Class and I wanted it to be easily extendable, so that if I wanted to quickly make stack out of it, I can just write push, pop, and peek methods and so forth.
Currently, my code looks like this. Note that I use 'Base' as my generic type.
namespace ClassLibrary1
{
public class LinkedList<Base> where Base : class
{
public class Node
{
private Node next;
private Node prev;
private Base value;
/// <summary>
/// Constructor for Nodes of Circular Linked List class.
/// Calls overloaded constructor for no previous or next provided.
/// O(1)
/// </summary>
/// <param name="value">The value to be stored. Can use tuple for associations</param>
public Node(Base value)
{
new Node(null, null, value);
}
/// <summary>
/// Constructor for nodes of Circular Linked List class.
/// O(1)
/// </summary>
/// <param name="prev">The previous node in the linked list</param>
/// <param name="next">The next node in the linked list</param>
/// <param name="value">The value to be stored</param>
public Node(Node prev, Node next, Base value)
{
this.prev = prev;
this.next = next;
this.value = value;
}
/// <summary>
/// Sets the 'next' attribute of the node to the passed value.
/// O(1)
/// Chainable
/// </summary>
/// <param name="next">The new value of the 'next' attribute.</param>
/// <returns>Chainable(Node, this)</returns>
public Node setNext(Node next)
{
this.next = next;
return this;
}
/// <summary>
/// Sets the 'prev' attribute of the node to the passed value
/// O(1)
/// Chainable
/// </summary>
/// <param name="prev">The new value of the 'prev' attribute to denote the previous node</param>
/// <returns>Chainable(Node, this)</returns>
public Node setPrev(Node prev)
{
this.prev = prev;
return this;
}
/// <summary>
/// Changes the stored value of type Base to the passed value.
/// O(1)
/// Chainable
/// </summary>
/// <param name="value">The new value to be stored with the node</param>
/// <returns>Chainable(Node, this)</returns>
public Node setVal(Base value)
{
this.value = value;
return this;
}
/// <summary>
/// Returns the next node in the linked list.
/// O(1)
/// </summary>
/// <returns>The next node in the linked list.(Node)</returns>
public Node getNext()
{
return this.next;
}
/// <summary>
/// Returns the previous node in the linked list.
/// O(1)
/// </summary>
/// <returns>The previous node in the linked list.(Node)</returns>
public Node getPrev()
{
return this.prev;
}
/// <summary>
/// Returns the value stored at this node.
/// O(1)
/// </summary>
/// <returns>The value stored at this node.(Base)</returns>
public Base getVal()
{
return this.value;
}
}
public Node head;
public bool duplicates;
public bool hasNullValues;
public bool throwNullError;
/// <summary>
/// Constructor for the LinkedList. Creates a null head node.
/// Duplication defaulted to false
/// O(1)
/// </summary>
public LinkedList()
{
this.head = new Node(null);
this.head.setNext(this.head).setPrev(this.head);
this.duplicates = false;
this.hasNullValues = false;
this.throwNullError = false;
}
/// <summary>
/// Allows duplication for the linked list.
/// O(1)
/// Chainable attribute.
/// </summary>
/// <returns>Chainable.(LinkedList<Base>, this)</returns>
public LinkedList<Base> hasDuplicates()
{
this.duplicates = true;
return this;
}
/// <summary>
/// Allows the structure to store null values in nodes.
/// O(1)
/// Chainable.
/// </summary>
/// <returns>Chainable.(LinkedList<Base>, this)</returns>
public LinkedList<Base> hasNulls()
{
this.hasNullValues = true;
return this;
}
/// <summary>
/// Causes the structure to throw a null error when a null value is inserted.
/// If hasNulls is off, turns it on.
/// O(1)
/// Chainable.
/// </summary>
/// <returns>Chainable.(LinkedList<Base>, this)</returns>
public LinkedList<Base> throwsNulls()
{
if (!this.hasNullValues)
{
this.hasNullValues = true;
}
this.throwNullError = true;
return this;
}
/// <summary>
/// Iff duplicates not allowed, searches for value in list. Throws error if duplicate found.
/// Creates a new node at the end of the list, then links it to the head node.
/// O(length) [if hasDuplicates()]
/// O(1) [if else]
/// Chainable
/// </summary>
/// <param name="value">Value stored at the new node in the list</param>
/// <returns>Chainable.(LinkedList<Base>, this)</returns>
public LinkedList<Base> add(Base value)
{
if (!duplicates)
{
if (search(value) != null)
{
throw new Exception("Value already exists in the linked list.");
}
}
if (!this.hasNullValues && value != null)
{
if (this.throwNullError)
{
throw new Exception("Cannot insert null values");
}
else
{
return this;
}
}
Node newNode = new Node(value);
this.head.getPrev().setNext(newNode);
this.head.setPrev(newNode);
return this;
}
/// <summary>
/// Iterates through the list until first such node for with a matching value is found.
/// Returns null if no matches found.
/// Use searchAll to find duplicates.
/// O(length)
/// </summary>
/// <param name="value">The value to be searched for.</param>
/// <returns>First node with the desired value(Node?)</returns>
public Node search(Base value)
{
Node temp = this.head.getNext();
while (!temp.getVal().Equals(value))
{
if (temp.Equals(this.head))
{
return null;
}
temp = temp.getNext();
}
return temp;
}
/// <summary>
/// If value doesn't exist in the list, throws an exception.
/// Deletes the first node found with the chosen value.
/// Use DeleteAll to delete all instances.
/// Chainable.
/// O(length)
/// </summary>
/// <param name="value">Value to be removed from the list.</param>
/// <returns>Chainable.(LinkedList<Base>, this)</returns>
public LinkedList<Base> delete(Base value)
{
try{
return delete(search(value));
}
catch(Exception e){
throw new Exception("Node to be deleted not found");
}
}
/// <summary>
/// Removes all pointers to the passed node.
/// O(1)
/// </summary>
/// <param name="tbd">The node to be deleted.</param>
/// <returns>Chainable.(LinkedList<Base>, this)</returns>
public LinkedList<Base> delete(Node tbd)
{
if (tbd.Equals(this.head))
{
throw new Exception("Cannot delete head node");
}
else
{
tbd.getPrev().setNext(tbd.getNext());
tbd.getNext().setPrev(tbd.getPrev());
}
return this;
}
/// <summary>
/// Returns a LinkedList of all nodes containing the desired value.
/// O(length)
/// </summary>
/// <param name="value">The value to be found.</param>
/// <returns>A LinkedList of Nodes with matching values.(LinkedList<Node>)</returns>
public LinkedList<Node> searchAll(Base value)
{
LinkedList<Node> returnList = new LinkedList<Node>();
Node temp = this.head.getNext();
while (!temp.Equals(this.head))
{
if (temp.getVal().Equals(value))
{
returnList.add(temp);
}
temp = temp.getNext();
}
return returnList;
}
/// <summary>
/// Returns the first Node in the Linked List.
/// O()
/// </summary>
/// <returns>First non-head node in the list.(Node)</returns>
public Node firstOrDefault()
{
return this.head.getNext();
}
/// <summary>
/// Returns the value of the first node in the list.
/// O(1)
/// </summary>
/// <returns>FIrst non-head </returns>
public Base firstVal()
{
return this.head.getNext().getVal();
}
/// <summary>
/// Gets the last node in the linked list.
/// O(1)
/// </summary>
/// <returns>The last node in the linked list.(Node)</returns>
public Node tail()
{
return this.head.getPrev();
}
/// <summary>
/// Returns the value of the last node in the linked list.
/// O(1)
/// </summary>
/// <returns>VThe value of the tail node.(Base)</returns>
public Base tailVal()
{
return this.head.getPrev().getVal();
}
public static void Main()
{
LinkedLis t<Int32> mine = new LinkedList<Int32>();
}
}
}
However, it gives Red Text under the Int32, saying "The type 'int' must be a reference type in order to use it as a parameter 'Base' in the generic type or method ---this---.
Tell me if you would like me to remove the comments, I'm not sure if that makes it harder or easier to solve.

Because you declared a constraint on a Base type to be a class (a reference type):
public class LinkedList<Base> where Base : class
It exactly forbids using Int32, because it's a value type and is different from a required reference type.
new LinkedList<Int32>()
So, to fix this particular problem, you would need to to create a wrapper class for your integer values.
Before you do this though, check your intentions to store any type in your linked list. Doing so you will strip you off all advantages of C# as a strongly typed language.
And as it was mentioned before, unless you write this code as a pure academic exercise, you should use an existing .NET LinkedList and possibly extend/inherit it, if you need more functionality.
Update: I assumed it went without saying, but to make it crystal clear don't forget that Nullable is a struct, not a class, so you cannot use "cheats" like int?.

Type.GetConstructor returns null on Iphone

I am developing an app in Xamarin for Iphone, android version of similar app is ready for Google play. I am using jabber-net library in my app for chat functionality. But having some issue on device(Iphone 5 - IOS 7.0.3). this issue doesn't occur in emulator following is the method code.
public class QnameType
{
/// <summary>
/// Element name
/// </summary>
protected internal string Name;
/// <summary>
/// Element namespace URI
/// </summary>
protected internal string NS;
/// <summary>
/// Type to create for NS/Name pair
/// </summary>
protected internal Type ElementType;
/// <summary>
/// Create a QnameType
/// </summary>
/// <param name="name"></param>
/// <param name="ns"></param>
/// <param name="typ"></param>
public QnameType(string name, string ns, Type typ)
{
this.Name = name;
this.NS = ns;
this.ElementType = typ;
}
/// <summary>
/// Is this the same qname by element name and namespace?
/// </summary>
/// <param name="obj"></param>
/// <returns></returns>
public override bool Equals(object obj)
{
if (obj == (object)this)
return true;
QnameType other = obj as QnameType;
if (other == null)
return false;
return (other.Name == Name) && (other.NS == NS);
}
/// <summary>
/// Get a hash over the name and namespace.
/// </summary>
/// <returns></returns>
public override int GetHashCode()
{
return ToString().GetHashCode();
}
/// <summary>
/// Namespace|Name
/// </summary>
/// <returns></returns>
public override string ToString()
{
return NS + "|" + Name;
}
}
public interface IPacketTypes
{
/// <summary>
/// QName to type mappings.
/// </summary>
QnameType[] Types { get; }
}
public class ElementFactory
{
private Hashtable m_types = new Hashtable();
private static readonly Type[] s_constructorTypes =
new Type[] { typeof(string),
typeof(XmlQualifiedName),
typeof(XmlDocument) };
public void AddType(IPacketTypes list)
{
foreach (QnameType qn in list.Types)
{
this.AddType(qn.Name, qn.NS, qn.ElementType);
}
}
public void AddType(string localName, string ns, Type t)
{
Debug.Assert(t.IsSubclassOf(typeof(Element)));
ConstructorInfo ci = t.GetConstructor(s_constructorTypes);
Debug.Assert(ci != null);
AddType(new XmlQualifiedName(localName, ns), ci);
}
public Element GetElement(string prefix, XmlQualifiedName qname, XmlDocument doc)
{
ConstructorInfo ci = (ConstructorInfo) m_types[qname];
if (ci == null)
{
return new Element(prefix, qname, doc);
}
return (Element) ci.Invoke
(new object[] {prefix, qname, doc});
}
/// <summary>
/// Get a constructor for the appropriate type for the given qname.
/// </summary>
public ConstructorInfo this[XmlQualifiedName qname]
{
get { return (ConstructorInfo) m_types[qname]; }
}
}
t.GetConstructor() returns null on Iphone but works fine on simulator.
Edit: added more detail,
Any help will be highly appreciated.
Thanks

That's likely normal, depending on t itself - what type does it represent ?
By default the managed linker is disabled (Don't link) on the simulator builds. That means every type will be part of the application.
However the default for device builds is Link SDK. This means unused types (found using static analysis) are removed from the application. This allow reducing the size of the application (by not compiling/shipping the whole .NET BCL inside each app).
Static analysis cannot find detect dynamic use of code, e.g. reflection. If your application depends on reflection is needs to preserve the code: using the [Preserve] attribute, an XML file or adding some extra code that will give an hint to the linker to keep the required members.
See documentation for further details.

In addition to the answer from poupou:
If you're stumbling over this question because you have a similar issue with Unity3D then take a look onto this page: https://docs.unity3d.com/Manual/IL2CPP-BytecodeStripping.html
In general that page shows you how to make sure everything is included in IL2CPP builds:
Use [Preserve] keyword on you classes
or
Add a link.xml file into your Assets root

Required validation attribute and custom validators order

I have 3 entities.
Let's say I have Event entity, and 2 "derived" entities: Accident, Repair.
They provide some additional fields over Event entity.
Event have StartDate and EndDate which are always required so I mark them with [Required] attribute. That's ok. But I have some additional validation logic that checks if the Event is Repair, then some other Event fields are also required. For this I provide custom validator.
The problem is that the properties marked with [Required] attribute are always checked before other validators.
What I want achieve:
If Event is Accident I want to make Event.SomeField required.
Validation summary should show now contain 3 validation errors at the very first validation attempt.
How it behaves now:
If Event is Accident first validation attempt shows 2 errors of 2 properties marked as [Required]. Only after I fill those, on the next validation attempt fires my custom validator which also states that 3rd Event.SomeField is also required.
I want all the required fields to validate at the same time.
Is this possible? How to achieve this?

For the case that a property is required based on a certain condition, i use a custom attribute, that was initially provided by Jeff Handley in his blog.
Here´s the code of the Attribute:
[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter, AllowMultiple = true)]
public class ConditionallyRequiredAttribute : RequiredAttribute {
private MemberInfo _member;
/// <summary>
/// The name of the member that will return the state that indicates
/// whether or not the validated member is required.
/// </summary>
public string ConditionMember { get; private set; }
/// <summary>
/// The condition value under which this validator treats
/// the affected member as required.
/// </summary>
public object RequiredCondition { get; private set; }
/// <summary>
/// Comma-separated list of additional members to
/// add to validation errors. By default, the
/// <see cref="ConditionMember"/> is added.
/// </summary>
public string ErrorMembers { get; set; }
/// <summary>
/// Conditionally require a value, only when the specified
/// <paramref name="conditionMember"/> is <c>true</c>.
/// </summary>
/// <param name="conditionMember">
/// The member that must be <c>true</c> to require a value.
/// </param>
public ConditionallyRequiredAttribute(string conditionMember)
: this(conditionMember, true) { }
/// <summary>
/// Conditionally require a value, only when the specified
/// <paramref name="conditionMember"/> has a value that
/// exactly matches the <paramref name="requiredCondition"/>.
/// </summary>
/// <param name="conditionMember">
/// The member that will be evaluated to require a value.
/// </param>
/// <param name="requiredCondition">
/// The value the <paramref name="conditionMember"/> must
/// hold to require a value.
/// </param>
public ConditionallyRequiredAttribute(string conditionMember, object requiredCondition) {
this.ConditionMember = conditionMember;
this.RequiredCondition = requiredCondition;
this.ErrorMembers = this.ConditionMember;
}
/// <summary>
/// Override the base validation to only perform validation when the required
/// condition has been met. In the case of validation failure, augment the
/// validation result with the <see cref="ErrorMembers"/> as an additional
/// member names, as needed.
/// </summary>
/// <param name="value">The value being validated.</param>
/// <param name="validationContext">The validation context being used.</param>
/// <returns>
/// <see cref="ValidationResult.Success"/> if not currently required or if satisfied,
/// or a <see cref="ValidationResult"/> in the case of failure.
/// </returns>
protected override ValidationResult IsValid(object value, ValidationContext validationContext) {
if (this.DiscoverMember(validationContext.ObjectType)) {
object state = this.InvokeMember(validationContext.ObjectInstance);
// We are only required if the current state
// matches the specified condition.
if (Object.Equals(state, this.RequiredCondition)) {
ValidationResult result = base.IsValid(value, validationContext);
if (result != ValidationResult.Success && this.ErrorMembers != null && this.ErrorMembers.Any()) {
result = new ValidationResult(result.ErrorMessage,
result.MemberNames.Union(this.ErrorMembers.Split(',').Select(s => s.Trim())));
}
return result;
}
return ValidationResult.Success;
}
throw new InvalidOperationException(
"ConditionallyRequiredAttribute could not discover member: " + this.ConditionMember);
}
/// <summary>
/// Discover the member that we will evaluate for checking our condition.
/// </summary>
/// <param name="objectType"></param>
/// <returns></returns>
private bool DiscoverMember(Type objectType) {
if (this._member == null) {
this._member = (from member in objectType.GetMember(this.ConditionMember).Cast<MemberInfo>()
where IsSupportedProperty(member) || IsSupportedMethod(member)
select member).SingleOrDefault();
}
// If we didn't find 1 exact match, indicate that we could not discover the member
return this._member != null;
}
/// <summary>
/// Determine if a <paramref name="member"/> is a
/// method that accepts no parameters.
/// </summary>
/// <param name="member">The member to check.</param>
/// <returns>
/// <c>true</c> if the member is a parameterless method.
/// Otherwise, <c>false</c>.
/// </returns>
private bool IsSupportedMethod(MemberInfo member) {
if (member.MemberType != MemberTypes.Method) {
return false;
}
MethodInfo method = (MethodInfo)member;
return method.GetParameters().Length == 0
&& method.GetGenericArguments().Length == 0
&& method.ReturnType != typeof(void);
}
/// <summary>
/// Determine if a <paramref name="member"/> is a
/// property that has no indexer.
/// </summary>
/// <param name="member">The member to check.</param>
/// <returns>
/// <c>true</c> if the member is a non-indexed property.
/// Otherwise, <c>false</c>.
/// </returns>
private bool IsSupportedProperty(MemberInfo member) {
if (member.MemberType != MemberTypes.Property) {
return false;
}
PropertyInfo property = (PropertyInfo)member;
return property.GetIndexParameters().Length == 0;
}
/// <summary>
/// Invoke the member and return its value.
/// </summary>
/// <param name="objectInstance">The object to invoke against.</param>
/// <returns>The member's return value.</returns>
private object InvokeMember(object objectInstance) {
if (this._member.MemberType == MemberTypes.Method) {
MethodInfo method = (MethodInfo)this._member;
return method.Invoke(objectInstance, null);
}
PropertyInfo property = (PropertyInfo)this._member;
return property.GetValue(objectInstance, null);
}
#if !SILVERLIGHT
/// <summary>
/// The desktop framework has this property and it must be
/// overridden when allowing multiple attributes, so that
/// attribute instances can be disambiguated based on
/// field values.
/// </summary>
public override object TypeId {
get { return this; }
}
#endif
}
Here´s an example:
public class Dummy{
public bool IsCondition {get; set;}
[ConditionallyRequired("IsCondition", true)]
public string SometimesRequired {get; set;}
}

WCF Known Type from System.Object in Config

I'm trying to specify a known type in my config, but I'm having problems with the fact that it derives from Object. I can make it work specifying the known type via attribute. But in this case I need to make it work from the config.
Here's an example. The following works fine:
[ServiceContract]
[ServiceKnownType(typeof(MyData))]
public interface IContract
{
[OperationContract]
void Send(object data);
}
[DataContract]
public class MyData
{
[DataMember]
public string Message { get; set; }
}
But if I remove the ServiceKnownType attribute and put the following in the config:
<system.runtime.serialization>
<dataContractSerializer>
<declaredTypes>
<add type="System.Object, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
<knownType type="WpfApplication1.MyData, WpfApplication1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"/>
</add>
</declaredTypes>
</dataContractSerializer>
</system.runtime.serialization>
I get a ConfigurationErrorsException with the message "The value for the property 'type' is not valid. The error is: The type System.Object cannot be used as a declared type in config."
Is there anyway to make this work via config?

The answer turns out to be it's not possible to do what I want to do in the config file alone. The config above corresponds to the [KnownType] attribute used on DataContracts. There appears to be no way to implement [ServiceKnownType] in the config.
An alternate approach is to use [ServiceKnownType(methodName, type)] attribute with a custom configuration section. The new config looks like this:
<configuration>
<configSections>
<section
name="serviceKnownTypes"
type="WpfApplication1.ServiceKnownTypesSection, WpfApplication1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"/>
</configSections>
<serviceKnownTypes>
<declaredServices>
<serviceContract type="WpfApplication1.IContract, WpfApplication1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null">
<knownTypes>
<knownType type="WpfApplication1.MyData, WpfApplication1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"/>
</knownTypes>
</serviceContract>
</declaredServices>
</serviceKnownTypes>
</configuration>
The contracts:
[ServiceContract]
[ServiceKnownType("GetServiceKnownTypes", typeof(KnownTypeHelper))]
public interface IContract
{
[OperationContract]
void Send(object data);
}
[DataContract]
public class MyData
{
[DataMember]
public string Message { get; set; }
}
The helper class that contains the callback that returns the list of known types
public static class KnownTypeHelper
{
public static IEnumerable<Type> GetServiceKnownTypes(ICustomAttributeProvider provider)
{
List<Type> result = new List<Type>();
ServiceKnownTypesSection serviceKnownTypes = (ServiceKnownTypesSection)ConfigurationManager.GetSection("serviceKnownTypes");
DeclaredServiceElement service = serviceKnownTypes.Services[((Type)(provider)).AssemblyQualifiedName];
foreach (ServiceKnownTypeElement knownType in service.KnownTypes)
{
result.Add(knownType.Type);
}
return result;
}
}
Information on creating custom config sections can be found here:
http://msdn.microsoft.com/en-us/library/2tw134k3.aspx
http://msdn.microsoft.com/en-us/library/system.configuration.configurationcollectionattribute.aspx

I'm not sure if it is by design, but the KnownTypeHelper below won't throw an error if you've not declared a service contract with known types. (i.e. its optional to add known types to service contracts).
using System;
using System.Collections.Generic;
using System.Configuration;
using System.Reflection;
/// <summary>
/// Helper for finding the known types for Wcf Services from a configuration file.
/// </summary>
public static class KnownTypeHelper
{
/// <summary>
/// Gets the known types for the service from a configuration file.
/// </summary>
/// <param name="provider">
/// The provider.
/// </param>
/// <returns>
/// The known types for the service from a configuration file.
/// </returns>
public static IEnumerable<Type> GetServiceKnownTypes(ICustomAttributeProvider provider)
{
var result = new List<Type>();
var serviceKnownTypes = (ServiceKnownTypesSection)ConfigurationManager.GetSection("serviceKnownTypes");
if (serviceKnownTypes != null)
{
var service = serviceKnownTypes.Services[((Type)provider).AssemblyQualifiedName];
if (service != null)
{
foreach (ServiceKnownTypeElement knownType in service.KnownTypes)
{
result.Add(knownType.Type);
}
}
}
return result;
}
}
To save someone else the trouble of creating the configuration classes,
Note: There is no validation of the assembly qualified type names. If someone wants to add the appropiate attributes to do this, please do.
using System.Configuration;
/// <summary>
/// Section for configuration known types for services.
/// </summary>
public class ServiceKnownTypesSection : ConfigurationSection
{
/// <summary>
/// Gets services.
/// </summary>
[ConfigurationProperty("declaredServices", IsDefaultCollection = false)]
[ConfigurationCollection(typeof(DeclaredServiceElement), AddItemName = "serviceContract", CollectionType = ConfigurationElementCollectionType.AddRemoveClearMap)]
public DeclaredServiceElementCollection Services
{
get
{
return (DeclaredServiceElementCollection)base["declaredServices"];
}
}
}
/// <summary>
/// Collection of declared service elements.
/// </summary>
public class DeclaredServiceElementCollection : ConfigurationElementCollection
{
/// <summary>
/// Gets the service for which known types have been declared for.
/// </summary>
/// <param name="key">
/// The key of the service.
/// </param>
public new DeclaredServiceElement this[string key]
{
get
{
return (DeclaredServiceElement)BaseGet(key);
}
set
{
var element = BaseGet(key);
var index = this.BaseIndexOf(element);
if (BaseGet(index) != null)
{
BaseRemoveAt(index);
}
BaseAdd(index, value);
}
}
/// <summary>
/// When overridden in a derived class, creates a new <see cref="T:System.Configuration.ConfigurationElement"/>.
/// </summary>
/// <returns>
/// A new <see cref="T:System.Configuration.ConfigurationElement"/>.
/// </returns>
protected override ConfigurationElement CreateNewElement()
{
return new DeclaredServiceElement();
}
/// <summary>
/// Gets the element key for a specified configuration element when overridden in a derived class.
/// </summary>
/// <returns>
/// An <see cref="T:System.Object"/> that acts as the key for the specified <see cref="T:System.Configuration.ConfigurationElement"/>.
/// </returns>
/// <param name="element">
/// The <see cref="T:System.Configuration.ConfigurationElement"/> to return the key for.
/// </param>
protected override object GetElementKey(ConfigurationElement element)
{
return ((DeclaredServiceElement)element).Type;
}
}
/// <summary>
/// The service for which known types are being declared for.
/// </summary>
public class DeclaredServiceElement : ConfigurationElement
{
/// <summary>
/// Gets or sets Type.
/// </summary>
[ConfigurationProperty("type", IsRequired = true, IsKey = true)]
public string Type
{
get
{
return (string) this["type"];
}
set
{
this["type"] = value;
}
}
/// <summary>
/// Gets KnownTypes.
/// </summary>
[ConfigurationProperty("knownTypes", IsDefaultCollection = false)]
[ConfigurationCollection(typeof(DeclaredServiceElement), AddItemName = "knownType", CollectionType = ConfigurationElementCollectionType.AddRemoveClearMap)]
public ServiceKnownTypeElementCollection KnownTypes
{
get
{
return (ServiceKnownTypeElementCollection)base["knownTypes"];
}
}
}
/// <summary>
/// A collection of known type elements.
/// </summary>
public class ServiceKnownTypeElementCollection : ConfigurationElementCollection
{
/// <summary>
/// Gets an known type with the specified key.
/// </summary>
/// <param name="key">
/// The key of the known type.
/// </param>
public new ServiceKnownTypeElement this[string key]
{
get
{
return (ServiceKnownTypeElement)BaseGet(key);
}
set
{
var element = BaseGet(key);
var index = this.BaseIndexOf(element);
if (BaseGet(index) != null)
{
BaseRemoveAt(index);
}
BaseAdd(index, value);
}
}
/// <summary>
/// When overridden in a derived class, creates a new <see cref="T:System.Configuration.ConfigurationElement"/>.
/// </summary>
/// <returns>
/// A new <see cref="T:System.Configuration.ConfigurationElement"/>.
/// </returns>
protected override ConfigurationElement CreateNewElement()
{
return new ServiceKnownTypeElement();
}
/// <summary>
/// Gets the element key for a specified configuration element when overridden in a derived class.
/// </summary>
/// <returns>
/// An <see cref="T:System.Object"/> that acts as the key for the specified <see cref="T:System.Configuration.ConfigurationElement"/>.
/// </returns>
/// <param name="element">
/// The <see cref="T:System.Configuration.ConfigurationElement"/> to return the key for.
/// </param>
protected override object GetElementKey(ConfigurationElement element)
{
return ((ServiceKnownTypeElement)element).Type;
}
}
/// <summary>
/// Configuration element for a known type to associate with a service.
/// </summary>
public class ServiceKnownTypeElement : ConfigurationElement
{
/// <summary>
/// Gets or sets TypeString.
/// </summary>
[ConfigurationProperty("type", IsRequired = true, IsKey = true)]
public string TypeString
{
get
{
return (string)this["type"];
}
set
{
this["type"] = value;
}
}
/// <summary>
/// Gets or sets Type.
/// </summary>
public Type Type
{
get
{
return Type.GetType(this.TypeString);
}
set
{
this["type"] = value.AssemblyQualifiedName;
}
}
}