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Cannot access inherited property if class has nested class of same name

I want to access a property of some class of mine, but get compiler error "CS0572 - Cannot reference a type through an expression".
I have the following setup
public interface IHelper {
void DoHelp();
}
public abstract class ClassWithHelperBase<THelper> where THelper : IHelper {
public THelper Helper { get; }
}
public class ClassWithHelper : ClassWithHelperBase<ClassWithHelper.Helper> {
// use a nested class, since there will be n classes deriving from ClassWithHelper and giving each helper a readable name (in this example ClassWithHelperHelper) is ugly
public class Helper : IHelper {
public static void SomeStaticMethod() { }
public void DoHelp() { }
}
}
public class Test {
private ClassWithHelper myClass;
public void DoTest() {
((ClassWithHelperBase<ClassWithHelper.Helper>) myClass).Helper.DoHelp(); // this works, but is ugly
myClass.Helper.DoHelp(); // what I want, but it's not working
//myClass.Helper.SomeStaticMethod(); // funnily IDE supposes static methods here even though the resulting code is invalid, since I am (obviously) not referencing the class type
}
}
The interface is unnecessary for reproduction, I added it for clarity.
Note: I do not want to call a static method, I just added it, to show the IDE mixes up the member and the class qualifier.
Is there a way to access the property Helper of myClass, without casting myClass or renaming the nested class?
Aka: Why can't the compiler distinguish the member and the nested class?

The problems is due to name collision between Helper class (type) and Helper property. Try this
public interface IHelper
{
void DoHelp();
}
public abstract class ClassWithHelperBase<THelper> where THelper : IHelper
{
public THelper Helper { get; set; }
}
public class ClassWithHelper : ClassWithHelperBase<ClassWithHelper.CHelper>
{
// use a nested class, since there will be n classes deriving from ClassWithHelper and giving each helper a readable name (in this example ClassWithHelperHelper) is ugly
public class CHelper : IHelper
{
public static void SomeStaticMethod() {}
public void DoHelp() { }
}
}
public class Test
{
private ClassWithHelper myClass;
public void DoTest() {
myClass.Helper.DoHelp();
ClassWithHelper.CHelper.SomeStaticMethod();
}
}
Here I renamed Helper class to the CHelper, so compiler can now distinguish class and property and thus the line myClass.Helper.DoHelp(); now works without cast.
If a "do not rename nested class" requirement is absolutely mandatory, then the problem may be also solved by renaming the Helper property in the base class to avoid name collision. However, I can't imagine better name for the property.
Unfortunately, for the static method, you can't reference myClass instance. So, you will need reference the whole type.

Is there a way to specify "type of current class" in a C# method signature?

I'm trying to define an abstract class which other classes will extend, and they have to be able to serialize themselves to JSON and deserialize from JSON. I want to write the abstract class something like this:
public abstract class BaseApiModel {
public abstract string ToJson();
public abstract T FromJson(string json);
}
... where T is the type of the current class. I would then write an extending class like this:
public class ContactApiModel : BaseApiModel {
public string ContactName { get; set; }
[...other properties...]
public override string ToJson() {
[...return serialized JSON string...]
}
public override ContactApiModel FromJson(string json) {
[...return deserialized object...]
}
}
Of course this doesn't work because T in the abstract class isn't defined. But is there some way I can write "this method has to return the type of the current class" in C#? Do I just going to have to make it return object? Or am I approaching this wrong and there's a better way to structure it?

You can declare your base class using generics, and in your ContactApiModel class just set the T parameter to be ContactApiModel, as the following:
public abstract class BaseApiModel<T> {
...
public abstract T FromJson(string json);
}
public class ContactApiModel : BaseApiModel<ContactApiModel> {
...
public override ContactApiModel FromJson(string json) {
[...return deserialized object...]
}
}

For future visitors of this:
A smarter solution would be to not implement that method at all in the corresponding classes and instead use extension methods:
public static class ExtendBaseApiModel
{
public static string ToJson(this T obj) { /* ... */ }
public static T FromJson<T>(this T obj, string json) where T : BaseApiModel { /* ... */ }
}
this will allow you to keep your classes nice and clean + free from serialization hazzle.
still .. there are some words to say
How to de-serialize proper
Assuming this is done to provide custom serialization inside the ToJson method and custom deserialization inside the FromJson method, then you should not use your own weirdo methods but rather let the framework do it for you.
For Json.NET, this should be done by utilizing the JsonConverter attribute onto the class and implementing a corresponding JsonConverter somewhere
Fun Fact
Combining the extension methods variant with the upper mentioned JsonConverter, you will be able to just serialize about every object by just calling myobjvar.ToJson(...)

DataContract inherit from a non-DataContract base class

Is it possible (and if so then how) to inherit from a base class that doesn't implement [DataContract] and tell the serializer to ignore it?
So something like
//Non-accessible, non-[DataContract] class
public class ThirdPartyOrFrameworkClass
{
public void ConvenienceMethod()
{
//Code
}
//Rest of the class
}
[DataContract (IgnoreBaseClassWhenSerializing = true)]
public class SomeStateClass : ThirdPartyOrFrameworkClass
{
[DataMember]
string _data;
//Rest of the class
}
If not, what's the solution to using a class that doesn't implement the [DataContract] attribute?
I'd prefer to use the DataContractSerializer than the XmlSerializer?

I think the answer to your question in NO (if you can't change the ThirdPartyOrFrameworkClass source code).

Why is a nested public class less accessible than it's parent?

I have the following classes:
public abstract class Navigator<T> where T : Navigator.Route
{
public class Route
{
}
}
public class P2PNavigator : Navigator<P2PNavigator.Route>
{
public class Route : Navigator.Route
{
}
}
During compilation I receive two errors.
Inconsistent accessibility: constraint type 'Navigator.Route' is less accessible than Navigator<T>'
Inconsistent accessibility: base class 'Navigator.Route' is less accessible than class 'P2PNavigator.Route'
Everything has public accessibility. What am I missing to make this work? I realise I could ultimately make them all namespace level classes, but I would prefer to have nesting.
EDIT: Thanks to the answers, I found the root cause of the problem was my partial classes weren't defined properly.
public partial abstract class Navigator<T> where T : Navigator.Route
{
}
partial class Navigator // Different to Navigator<T> and implicitly internal.
{
public class Route
{
}
}

Navigator.Route is not the same as Navigator<P2PNavigator.Route>.Route and should be giving you other errors.
Code that specifies types correctly compiles ok:
public abstract class Navigator<T> where T : Navigator<T>.Route
{
public class Route
{
}
}
public class P2PNavigator : Navigator<P2PNavigator.Route>
{
public class Route : Navigator<P2PNavigator.Route>.Route
{
}
}
You probably have some non-generic Navigator class that makes your sample comile with errors you see.

The non-generic type 'System.Collections.IEnumerable' cannot be used with type arguments

using System.Collections.Generic;
public sealed class LoLQueue<T> where T: class
{
private SingleLinkNode<T> mHe;
private SingleLinkNode<T> mTa;
public LoLQueue()
{
this.mHe = new SingleLinkNode<T>();
this.mTa = this.mHe;
}
}
Error:
The non-generic type 'LoLQueue<T>.SingleLinkNode' cannot be used with type arguments
Why do i get this?

If you want to use IEnumerable<T>, as your post's title suggests, you need to include using System.Collections.Generic;.
As for the SingleLinkNode class, I don't know where you got it, it's not part of the .NET framework that I can see. I'd guess that it isn't implemented using generics, and you'll need to add a bunch of casts from object to T everywhere.

I'm pretty sure you haven't defined your SingleLinkNode class as having a generic type parameter. As such, an attempt to declare it with one is failing.
The error message suggests that SingleLinkNode is a nested class, so I suspect what may be happening is that you are declaring members of SingleLinkNode of type T, without actually declaring T as a generic parameter for SingleLinkNode. You still need to do this if you want SingleLinkNode to be generic, but if not, then you can simply use the class as SingleLinkNode rather than SingleLinkNode<T>.
Example of what I mean:
public class Generic<T> where T : class
{
private class Node
{
public T data; // T will be of the type use to construct Generic<T>
}
private Node myNode; // No need for Node<T>
}
If you do want your nested class to be generic, then this will work:
public class Generic<T> where T : class
{
private class Node<U>
{
public U data; // U can be anything
}
private Node<T> myNode; // U will be of type T
}

This compiles for me:
public sealed class SingleLinkNode<T>
{
}
public sealed class LoLQueue<T> where T : class
{
private SingleLinkNode<T> mHe;
private SingleLinkNode<T> mTa;
public LoLQueue()
{
this.mHe = new SingleLinkNode<T>();
this.mTa = this.mHe;
}
}
You'll need to post your SingleLinkNode class for further answers...
John