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Getting a value from a generic method without supplying the type

I was trying to create a class were one of the properties was generic without the class itself being generic. I discover that you can't do that; generic properties aren't allowed. A bit of digging here too me to the thread Making a generic property were I found a work around that works nicely for me.
Subsequently, I ended up with this class...
[Serializable]
public class ConfigurationItem
{
private readonly Type type;
public string Description { get; set; }
public IDictionary<string, ConfigurationItem> Items { get; private set; }
public string Name { get; set; }
public string Summary { get; set; }
public object Value { get; private set; }
public ConfigurationItem(string name, Type type = null, object value = null)
{
this.Name = name;
this.type = type ?? typeof(string);
this.Value = value;
Items = new Dictionary<string, ConfigurationItem>();
}
public string Export()
{
return JsonConvert.SerializeObject(this);
}
public T GetValue<T>()
{
return (T)Convert.ChangeType(Value, type);
}
}
Now the only issue I have is that if I want to get the value, properly cast, I have to supply the type when I call GetValue(). Instinctively, I can't help but feel, given that the class knows the type that should be returned, it should be possible for me to construct a GetValue() method that doesn't require any additional information from me.
I can't figure out how.
I did find the thread Getting a generic method to infer the type parameter from the runtime type which appears to suggest that it is possible, but I understand very little about Reflection and couldn't make any sense of what was being said.
Is there a way of constructing a GetType() method that doesn't require that I supply the generic type? And can you explain it in a way that my feeble brain can comprehend it?
EDIT
A number of people have actually pointed out that really I don't need to do this anyway, nonetheless as a learning exercise I followed up the suggestion from #ShoaibShakeel to look at the C# dynamic type and came up with these additional methods...
public dynamic GetValue()
{
return typeof(ConfigurationItem)
.GetMethod("GetReturnValue", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance)
.MakeGenericMethod(type)
.Invoke(this, new object[] { });
}
private T GetReturnValue<T>()
{
return (T)Convert.ChangeType(Value, type);
}

Instinctively, I can't help but feel, given that the class knows the type that should be returned
While it is true that the Value object knows its own type, this information is only available at runtime though (once there is an actual object that has a type). So in order to have type information at compile time, you need to supply the necessary information. After all, it’s impossible to know statically what object is being assigned there.
But assuming that GetValue() was able to return the typed object automatically, what would you want to do with it?
var x = configurationItem.GetValue();
So what type should x be of, and what would you want to do with it afterwards? Do you only want to print it or something? Then object is enough. Do you want to calculate something with it? Then you would already require that it’s an int, or a float or something, so you would need an actual static type—which is why you would have to supply that type information.
Just because the return type is object that does not mean that the object itself loses the type information. A string assigned to an object property will still be a string, even if you retrieve it much later. And if you expect a string and want to do something with it, then you can surely just cast it to a string.

No.
The compiler cannot infer the type from the variable it is assigned to since it is ambiguous, especially in large inheritance trees.
Consider the line
object o = configurationItem.GetValue<int>();
int may be a valid conversion for your value but object isn't, since objectdoes not implement the IConvertible interface (required by Convert.ChangeType().

I was able to get my class to return a value, cast correctly, using reflection and dynamics using the following additions to my original class.
public dynamic GetValue()
{
return typeof(ConfigurationItem)
.GetMethod("GetReturnValue", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance)
.MakeGenericMethod(type)
.Invoke(this, new object[] { });
}
private T GetReturnValue<T>()
{
return (T)Convert.ChangeType(Value, type);
}

How to write a method to accept a type as a parameter and use it within the method body to cast another variable into that passed type?

What I want is to have a method that accepts a type as a parameter and cast a variable into that type within the method in C#
as an example I want to pass a UI element to this helper method and extract its DataContext's (which is bound dynamically at runtime) Description. I want to use this method in a more generalized manner so that I can pass in the DataContext's type also.
private String GetDescription(FrameworkElement element, Type type) {
return (element.DataContext as type).Description;
//or
//return ((type)element.DataContext).Description;
}
both the ways it ends up with a compile time error.
I tried using generics as well but it was not successful as i might not understood properly.
It would be really great if someone could explain how to do this in a simple manner.

Write a interface and implement it for your classes:
public interface IDescribable
{
string Description{get;}
}
Implement this object on your desired classes:
public class MyClass:IDescribable
{
// other members
public string Description{get; set;}
}
Then you could even write an extension method to extract the string:
public static string GetDescription(this FrameworkElement element)
{
var contextData= element.DataContext as IDescribable;
return contextData!=null
? contextData.Description
:"";
}
Or if you don't want implement interface use reflection:
private string GetDescription(FrameworkElement element)
{
var decProp= element.DataContext.GetType().GetProperty("Description");
return decProp!=null
?decProp.GetValue(element.DataContext)
:"";
}

Initialize Property of Generic Type

I have read multiple posts but haven't found an appropriate answer for my problem.
But there has to be one. So please be patient if this post really is an duplicate.
I try to initialize a Property of a generic type implementing a generic interface.
My interface looks basically like this:
public interface IMyInterface<TType> : IMyInterface
{
TType Value {get; set;}
// ... and some more ...
}
public interface IMyInterface
{
SetValue(string value);
}
I have multiple Classes implementing IMyInterface without knowing them
at the piece of code, where I need to set the value.
Is it possible to inizialize the "Value"-Property without using the Name of the property?
(Is there a "nice" way to do this?) - It isn't possible to use SetValue< TType >
void SetValue(object obj, string value)
{
// object obj implements IMyInterface<???>
PropertyInfo valueInfo = typeof(obj).GetType().GetProperty("Value")
valueInfo.SetValue(obj, Activator.CreateInstance(valueInfo.PropertyType))
((IMyInterface)obj).SetValue(value);
}
Thanks in advance.
EDIT: - removed -
EDIT 2:
This structure is given:
public Interface IGeneric<TType> : INonGeneric
{
TType Value2 {get;}
}
public Interface INonGeneric
{
object Value1 {get;}
}
using "Value1" from reflection is really easy:
INonGeneric myObject = (INonGeneric)givenObject;
doSomething(myObject.Value1)
if i need to access "Value2" it isn't that easy. As one can see in my first example I had to use the following construct which not seems to be the best way to access "Value2", because the properties name is hardcoded.
PropertyInfo valueInfo = givenObject.GetType().GetProperty("Value2");
object value = (object)valueInfo.GetValue(givenObject);
Is there any better solution?

If i got you right you have and instance that implements IGeneric, and you want to access the property Value2 (which has a generic return type).
The thing is, Generics are for compile time type safety. You cannot cast your object to IGeneric<...> if you don't know the type parameter. So why do you want to use Generics anyway if you don't know the type parameter?
There is a solution for this "problem", it is the same as IEnumerable and IEnumerable< T> uses. it can look something like this:
public interface INonGeneric
{
object Value {get; }
}
public interface IGeneric<T>
{
T Value { get; }
}
public class Magic : INonGeneric, IGeneric<string>
{
object INonGeneric.Value { get { return this.Value; } }
public string Value { get { return "test"; } }
}
You can now use cast the Object to INonGeneric if you don't use the type parameter, or use the Generic implementation if you know the type parameter at compile time.
But if you want to access a property of a generic type (you have no control over) without knowing the type parameter you will not get around either reflection or dynamic.
The dynamic solution can look like this:
dynamic generic = givenObject;
object value2 = generic.Value2;

ReSharper warns: "Static field in generic type"

public class EnumRouteConstraint<T> : IRouteConstraint
where T : struct
{
private static readonly Lazy<HashSet<string>> _enumNames; // <--
static EnumRouteConstraint()
{
if (!typeof(T).IsEnum)
{
throw new ArgumentException(
Resources.Error.EnumRouteConstraint.FormatWith(typeof(T).FullName));
}
string[] names = Enum.GetNames(typeof(T));
_enumNames = new Lazy<HashSet<string>>(() => new HashSet<string>
(
names.Select(name => name), StringComparer.InvariantCultureIgnoreCase
));
}
public bool Match(HttpContextBase httpContext, Route route,
string parameterName, RouteValueDictionary values,
RouteDirection routeDirection)
{
bool match = _enumNames.Value.Contains(values[parameterName].ToString());
return match;
}
}
Is this wrong? I would assume that this actually has a static readonly field for each of the possible EnumRouteConstraint<T> that I happen to instance.

It's fine to have a static field in a generic type, so long as you know that you'll really get one field per combination of type arguments. My guess is that R# is just warning you in case you weren't aware of that.
Here's an example of that:
using System;
public class Generic<T>
{
// Of course we wouldn't normally have public fields, but...
public static int Foo;
}
public class Test
{
public static void Main()
{
Generic<string>.Foo = 20;
Generic<object>.Foo = 10;
Console.WriteLine(Generic<string>.Foo); // 20
}
}
As you can see, Generic<string>.Foo is a different field from Generic<object>.Foo - they hold separate values.

From the JetBrains wiki:
In the vast majority of cases, having a static field in a generic type
is a sign of an error. The reason for this is that a static field in a
generic type will not be shared among instances of different close
constructed types. This means that for a generic class C<T> which
has a static field X, the values of C<int>.X and C<string>.X
have completely different, independent values.
In the rare cases when you do need the 'specialized' static fields,
feel free to suppress the warning.
If you need to have a static field shared between instances with
different generic arguments, define a non-generic base class to
store your static members, then set your generic type to inherit from
this type.

This is not necessarily an error - it is warning you about a potential misunderstanding of C# generics.
The easiest way to remember what generics do is the following:
Generics are "blueprints" for creating classes, much like classes are "blueprints" for creating objects. (Well, this is a simplification though. You may use method generics as well.)
From this point of view MyClassRecipe<T> is not a class -- it is a recipe, a blueprint, of what your class would look like. Once you substitute T with something concrete, say int, string, etc., you get a class. It is perfectly legal to have a static member (field, property, method) declared in your newly created class (as in any other class) and no sign of any error here.
It would be somewhat suspicious, at first sight, if you declare static MyStaticProperty<T> Property { get; set; } within your class blueprint, but this is legal too. Your property would be parameterized, or templated, as well.
No wonder in VB statics are called shared. In this case however, you should be aware that such "shared" members are only shared among instances of the same exact class, and not among the distinct classes produced by substituting <T> with something else.

There are several good answers here already, that explain the warning and the reason for it. Several of these state something like having a static field in a generic type generally a mistake.
I thought I'd add an example of how this feature can be useful, i.e. a case where suppressing the R#-warning makes sense.
Imagine you have a set of entity-classes that you want to serialize, say to Xml. You can create a serializer for this using new XmlSerializerFactory().CreateSerializer(typeof(SomeClass)), but then you will have to create a separate serializer for each type. Using generics, you can replace that with the following, which you can place in a generic class that entities can derive from:
new XmlSerializerFactory().CreateSerializer(typeof(T))
Since your probably don't want to generate a new serializer each time you need to serialize an instance of a particular type, you might add this:
public class SerializableEntity<T>
{
// ReSharper disable once StaticMemberInGenericType
private static XmlSerializer _typeSpecificSerializer;
private static XmlSerializer TypeSpecificSerializer
{
get
{
// Only create an instance the first time. In practice,
// that will mean once for each variation of T that is used,
// as each will cause a new class to be created.
if ((_typeSpecificSerializer == null))
{
_typeSpecificSerializer =
new XmlSerializerFactory().CreateSerializer(typeof(T));
}
return _typeSpecificSerializer;
}
}
public virtual string Serialize()
{
// .... prepare for serializing...
// Access _typeSpecificSerializer via the property,
// and call the Serialize method, which depends on
// the specific type T of "this":
TypeSpecificSerializer.Serialize(xmlWriter, this);
}
}
If this class was NOT generic, then each instance of the class would use the same _typeSpecificSerializer.
Since it IS generic however, a set of instances with the same type for T will share a single instance of _typeSpecificSerializer (which will have been created for that specific type), while instances with a different type for T will use different instances of _typeSpecificSerializer.
An example
Provided the two classes that extend SerializableEntity<T>:
// Note that T is MyFirstEntity
public class MyFirstEntity : SerializableEntity<MyFirstEntity>
{
public string SomeValue { get; set; }
}
// Note that T is OtherEntity
public class OtherEntity : SerializableEntity<OtherEntity >
{
public int OtherValue { get; set; }
}
... let's use them:
var firstInst = new MyFirstEntity{ SomeValue = "Foo" };
var secondInst = new MyFirstEntity{ SomeValue = "Bar" };
var thirdInst = new OtherEntity { OtherValue = 123 };
var fourthInst = new OtherEntity { OtherValue = 456 };
var xmlData1 = firstInst.Serialize();
var xmlData2 = secondInst.Serialize();
var xmlData3 = thirdInst.Serialize();
var xmlData4 = fourthInst.Serialize();
In this case, under the hood, firstInst and secondInst will be instances of the same class (namely SerializableEntity<MyFirstEntity>), and as such, they will share an instance of _typeSpecificSerializer.
thirdInst and fourthInst are instances of a different class (SerializableEntity<OtherEntity>), and so will share an instance of _typeSpecificSerializer that is different from the other two.
This means you get different serializer-instances for each of your entity types, while still keeping them static within the context of each actual type (i.e., shared among instances that are of a specific type).

C# generic class accepting a inherited type.

**Preface I'm very new to generics. I have a class I created called Geno. My Peno class simply contains a string Name property. I'm wondering why I cannot call T.Name from within a method on this class. How would I access the properties on T? Any good resources on how this works?
public class Geno<T> where T : Peno
{
}
public string GetName()
{
return T.Name;
}

Is your Name property an instance property or a static property? If it's a static property, you don't get polymorphism anyway - you could just call Peno.Name.
If it's an instance property, you need an instance on which to call it. For example:
public class Geno<T> where T : Peno
{
private readonly T value;
public Geno(T value)
{
this.value = value;
}
public string GetName()
{
return value.Name;
}
}
If this doesn't help, please give a more complete example of what you're trying to do.

T is the type Peno. So what you try to do is Peno.Name, which is probably not what you want. Something like this would work:
public string GetName(T t)
{
return t.Name;
}

Static properties does not support inheritence. Hence you can just call Peno.Name rather than going for T.
If in your case you want to access a normal property, you need to create an instance of T which will let you call its property Name.

T is a Generic Type Parameter, not a parameter being passed into the class that is using T.
A Good example of this is List<T> you say this is a List, which means you are creating a list that contains object of the type of String.