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C# Collection of Different Generic Types Without Casting

I've found couple of questions on the same topic here, however I couldn't find what I need. Basically I am searching for this kind of magic:
public class BaseClass
{
public int DerivedТype { get; set; }
}
public class DerivedClass<T> : BaseClass
{
public DerivedClass(T initialValue)
{
DerivedТype = 1;
Property = initialValue;
}
public T Property { get; set; }
}
public class OtherDerivedClass<T> : BaseClass
{
public OtherDerivedClass(T initialValue)
{
DerivedТype = 2;
OtherProperty = initialValue;
}
public T OtherProperty { get; set; }
public int OtherProperty2 { get; set; }
public float OtherProperty { get; set; }
}
public class Program
{
public static void Main()
{
List<BaseClass> baseClassList = new List<BaseClass>();
baseClassList.Add(new DerivedClass<int>(5));
baseClassList.Add(new OtherDerivedClass<float>(6));
foreach (var derived in baseClassList)
{
if (derived.DerivedТype == 1)
{
Console.WriteLine(derived.Property);
}
else if (derived.DerivedТype == 2)
{
Console.WriteLine(derived.OtherProperty);
}
}
}
}
I want a list of BaseClass where I can insert instances of DerivedClass and OtherDerivedClass. So far so good.
DerivedClass and OtherDerivedClass hold different properties so I really have no idea how access them. Also I don't want to use any weired casts. So this part of the code prevents me from building.
if (derived.DerivedТype == 1)
{
Console.WriteLine(derived.Property);
}
else if (derived.DerivedТype == 2)
{
Console.WriteLine(derived.OtherProperty);
}
Any ideas would be appreciated. Thank you in advance!

This looks like a problem that can be solved with polymorphism. I'll make a version of your app that does exactly what you seem to be doing in your example, but if there was more information as to what your target goal is, the solution may be different.
public abstract class BaseClass
{
public abstract void DoSomething();
public abstract void GetData(Dictionary<string,string> container);
}
public class DerivedClass<T> : BaseClass
{
public DerivedClass(T initialValue)
{
Property = initialValue;
}
public T Property { get; set; }
public override void DoSomething()
{
Console.WriteLine(Property);
}
public override void GetData(Dictionary<string,string> container)
{
container.Add(nameof(Property), "{Property}");
}
}
public class OtherDerivedClass<T> : BaseClass
{
public OtherDerivedClass(T initialValue)
{
OtherProperty = initialValue;
}
public T OtherProperty { get; set; }
public int OtherProperty2 { get; set; }
public override void DoSomething()
{
Console.WriteLine(OtherProperty);
}
public override void GetData(Dictionary<string,string> container)
{
container.Add(nameof(OtherProperty), "{OtherProperty}");
container.Add(nameof(OtherProperty2), "{OtherProperty2}");
}
}
Your foreach loop could then be as simple as:
foreach(var derived in baseClassList) derived.DoSomething();
This is the proper way to do something like this using OO. There's no need for the DerivedType integer since the object knows what type of class it is and what to do. This is why one would use polymorphism. It's simple and elegant and OO. Extend or change the DoSomething to be more appropriate for what you're trying to do.
The OP came up with his own solution, but if the goal is to do something with the data that is more meaningful, you could also pass in an object to an abstract method that allows you to do this. I added a GetData method that will return all of the property values as strings. The second type of the dictionary could also be object with the actual value stored in the dictionary.
BaseClass could also be a regular class with a method in it to return an IDictionary of object values with string keys. The method could use reflection to get all property values for whatever class it is the base of. Reflection has much more overhead, though, so is not the most efficient way to do this from an execution standpoint.
The correct way to check if an object is a certain type is to use the is operator such as:
if(derived is DerivedType<int>)
{
// Do what you need to do with the specific object type
}
If you know you're going to cast the object, as pointed out by Adosi, you would use:
var castedValue = derived as DerivedType<int>;
if(castedValue != null)
{
// Do what you need to do with castedValue
}
A null will be returned if the object isn't of type DerivedType<int>. Trying to use (DerivedType)derived would cause an invalid cast exception.

To the best of my knowledge what you want is between impossible and not a good idea. Typechecking is done at compile time. Stuff like Dynamic can move those checks to runtime, but it results in all kinds of issues (functions that take dynamic parameters also return dynamic).
If you got at least C# 7.0, you can at least write a switch for it. Old switch only supported values vs constants for a few select value types and string. But C# 7.0 introduces pattern matching. With that you could even use a is check as part of a case.

Thank you all for the awesome support! I decided to go simple and just use a cast.
public class BaseClass
{
public int DataТype { get; set; }
public object Data { get; set; }
}
public class DataClass<T>
{
public DataClass(T initialValue)
{
Property = initialValue;
}
public T Property { get; set; }
}
public class Program
{
public static void Main(string[] args)
{
List<BaseClass> listBaseClass = new List<BaseClass>();
BaseClass dummy = new BaseClass();
dummy.DataТype = 1;
dummy.Data = new DataClass<int>(50);
listBaseClass.Add(dummy);
if (listBaseClass[0].DataТype == 1)
{
DataClass<int> casted = (DataClass<int>)listBaseClass[0].Data;
Console.WriteLine(casted.Property);
}
}
}

Unable to serialize a derived class to XML

I am trying to serialize following class hierarchy:
public class Control
{
public virtual string Name {get; set;}
public virtual string Type {get; set;}
public virtual string Text { get; set; }
public virtual SerializableFont Font { get; set; }
private Operation op = new Operation();
public Operation Events { get { return op; } }
}
[System.Xml.Serialization.XmlInclude(typeof(Control))]
public class TextProperties : Control
{
public Label txt;
public TextProperties()
{
}
public override string Type
{
get { return "Text"; }
}
public override string Text
{
get { return txt.Text; }
set
{
txt.Text = value;
}
}
public override SerializableFont Font
{
get { return new SerializableFont(txt.Font); }
set
{
txt.Font = new SerializableFont().Font ;
}
}
}
As you can see I am including the base class but still its throwing following exception:
The type TextProperties was not expected. Use the
XmlInclude or SoapInclude attribute to specify types that are not
known statically.

I´m not sure that the problem is really your class hierarchy itself, it seems to be okay. You dont need to add the attribute.
Instead, you are likely trying to read/write an object of type TextProperties with an XmlSerializer created for objects of type Control. That won´t work, you need to use the serializer created specific to the type to serialize / deserialize.
If this is not known at compile time, try to create a wrapping class that implements IXMLSerializable. When reading, this class must first read data to define the class of the wrapped object (a node attribute named "TypeName", for example). It must then create the specific serializer for the given type at runtime and use it to load the wrapped object.
EDIT: Here is some sample code how it could be done. You will need to implement GetTypeByName yourself (eg. crawling through all loaded assemblies or just "hardwiring" some strings to a specific type you expect). The code should suffice to be integrated into a class with a property "WrappedObject".
public XmlSchema GetSchema()
{
return null;
}
public void ReadXml(XmlReader reader)
{
reader.MoveToContent();
var typeName = reader.GetAttribute("TypeName");
reader.ReadStartElement();
var serializer = new XmlSerializer(GetTypeByName(typeName));
WrappedObject = serializer.Deserialize(reader);
reader.ReadEndElement();
}
public void WriteXml(XmlWriter writer)
{
writer.WriteAttributeString("TypeName", "", GetTypeByName(WrappedObject));
var serializer = new XmlSerializer(typeof(WrappedObject));
serializer.Serialize(writer, WrappedObject);
}

I think you need to put attribute above the parent class like this
[XmlInclude(typeof(ChildClass))]
[Serializable]
public abstract class ParentClass
{
public abstract string Name { get; set; }
}
in child class you put
[Serializable]
public class ChildClass: ParentClass
{
}

What is the best way to define a static property which is defined once per sub-class?

I wrote the following console app to test static properties:
using System;
namespace StaticPropertyTest
{
public abstract class BaseClass
{
public static int MyProperty { get; set; }
}
public class DerivedAlpha : BaseClass
{
}
public class DerivedBeta : BaseClass
{
}
class Program
{
static void Main(string[] args)
{
DerivedBeta.MyProperty = 7;
Console.WriteLine(DerivedAlpha.MyProperty); // outputs 7
}
}
}
As this console app demonstrates, the MyProperty property exists once for all instances of BaseClass. Is there a pattern to use which would allow me to define a static property which will have allocated storage for each sub-class type?
Given the above example, I would like all instances of DerivedAlpha to share the same static property, and all instances of DerivedBeta to share another instance of the static property.
Why am I trying to do this?
I am lazily initializing a collection of class property names with certain attributes (via reflection). The property names will be identical for each derived class instance, so it seems wasteful to store this in each class instance. I can't make it static in the base class, because different sub-classes will have different properties.
I don't want to replicate the code which populates the collection (via reflection) in each derived class. I know that one possible solution is to define the method to populate the collection in the base class, and call it from each derived class, but this is not the most elegant solution.
Update - Example of what I'm doing
At Jon's request, here's an example of what I'm trying to do. Basically, I can optionally decorate properties in my classes with the [SalesRelationship(SalesRelationshipRule.DoNotInclude)] attribute (there are other attributes, this is just a simplified example).
public class BaseEntity
{
// I want this property to be static but exist once per derived class.
public List<string> PropertiesWithDoNotInclude { get; set; }
public BaseEntity()
{
// Code here will populate PropertiesWithDoNotInclude with
// all properties in class marked with
// SalesRelationshipRule.DoNotInclude.
//
// I want this code to populate this property to run once per
// derived class type, and be stored statically but per class type.
}
}
public class FooEntity : BaseEntity
{
[SalesRelationship(SalesRelationshipRule.DoNotInclude)]
public int? Property_A { get; set; }
public int? Property_B { get; set; }
[SalesRelationship(SalesRelationshipRule.DoNotInclude)]
public int? Property_C { get; set; }
}
public class BarEntity : BaseEntity
{
public int? Property_D { get; set; }
[SalesRelationship(SalesRelationshipRule.DoNotInclude)]
public int? Property_E { get; set; }
public int? Property_F { get; set; }
}
Desired end result
Accessing FooEntity.PropertiesWithDoNotInclude returns a List<string> of:
{
"Property_A",
"Property_C"
}
Accessing BarEntity.PropertiesWithDoNotInclude returns a List<string> of:
{
"Property_E"
}

Two possible approaches:
Use attributes; decorate each subclass with an attribute, e.g.
[MyProperty(5)]
public class DerivedAlpha
{
}
[MyProperty(10)]
public class DerivedBeta
{
}
That only works when they're effectively constants, of course.
Use a dictionary:
var properties = new Dictionary<Type, int>
{
{ typeof(DerivedAlpha), 5) },
{ typeof(DerivedBeta), 10) },
};
EDIT: Now that we have more context, Ben's answer is a really good one, using the way that generics work in C#. It's like the dictionary example, but with laziness, thread-safety and simple global access all built in.

Jon has a good solution as usual, although I don't see what good attributes do here, since they have to be explicitly added to every subtype and they don't act like properties.
The Dictionary approach can definitely work. Here's another way to do that, which explicitly declares that there will be one variable per subclass of BaseEntity:
class FilteredProperties<T> where T : BaseEntity
{
static public List<string> Values { get; private set; }
// or static public readonly List<string> Values = new List<string>();
static FilteredProperties()
{
// logic to populate the list goes here
}
}
The drawback of this is that it's rather difficult to pair with a GetType() call such as you might use in methods of BaseEntity. A Dictionary, or wrapper thereto which implements lazy population, is better for that usage.

I just recently needed this same thing and came across this question. I think Jon's and Fried's ideas to use a Dictionary are on the right track but don't quite hit what I was looking for so I thought I'd show my own complete and very easy to extend implementation.
public class TypeStaticProperty<T>
{
T _defaultValue;
Dictionary<Type, T> _values = new Dictionary<Type, T>();
public TypeStaticProperty(T defalutValue = default)
{
_defaultValue = defalutValue;
}
public T Get(object caller)
{
lock (_values)
{
if (_values.TryGetValue(caller?.GetType(), out T val))
return val;
else
return _defaultValue;
}
}
public void Set(object caller, T val)
{
lock (_values)
_values[caller?.GetType()] = val;
}
}
And to demonstrate:
class TestBaseClass
{
static TypeStaticProperty<int> _property = new TypeStaticProperty<int>();
public int Property
{
get => _property.Get(this);
set => _property.Set(this, value);
}
}
class TestClass1 : TestBaseClass
{
}
class TestClass2 : TestBaseClass
{
}
class Program
{
static void Main(string[] args)
{
TestClass1 test1a = new TestClass1();
TestClass1 test1b = new TestClass1();
test1a.Property = 1;
test1b.Property = 2;
TestClass2 test2a = new TestClass2();
TestClass2 test2b = new TestClass2();
test2a.Property = 3;
test2b.Property = 4;
Console.WriteLine($"test1a.Property = {test1a.Property}");
Console.WriteLine($"test1b.Property = {test1b.Property}");
Console.WriteLine($"test2a.Property = {test2a.Property}");
Console.WriteLine($"test2b.Property = {test2b.Property}");
}
}
Output:
test1a.Property = 2
test1b.Property = 2
test2a.Property = 4
test2b.Property = 4
So while you still need a class instance to access and set the property, the value will always be the same across all instances of that precise type. (This includes generics too; Foo<int> will be seen as a different type than Foo<string>). This has the huge advantage over Fried's example in that you don't need to know at compile time the precise type whose "static" value you're looking for when accessing or setting.
PS - For full disclosure, this was heavily inspired by the WPF source code, which uses a very similar pattern for DependencyProperty's and all kinds of other internal bells and whistles designed to improve performance and reduce memory footprint.

Is it possible in C# make public virtual method private/internal in overriding class? [duplicate]

I want to hide the base public property(a data member) in my derived class:
class Program
{
static void Main(string[] args)
{
b obj = new b();
obj.item1 = 4;// should show an error but it doent ???
}
}
class a
{
public int item1 {get; set;}
public int item2 { get; set; }
}
class b : a
{
new private int item1;
}
class c : a
{
}
i have member as public because i want the member to be inherited in c class , but want to hide the member in b class , how can i do this ?
dont i have an option to selectively inherite the variable i want in my base class ??? thats really bad , i think ms should provide us with an option (may be a modifier) to perform this
Edit:
I found the answer myself (i heard lots of them telling this is not possible in c#, but you can kind of do it)
I am including the code in case it is useful
class Program
{
static void Main(string[] args)
{
b obj = new b();
obj.item1 = 4; // shows an error : )
}
}
class a
{
public int item1 { get; set; }
public int item2 { get; set; }
}
class b : a
{
new public static int item1
{
get;
private set;
}
}

I'm going to attempt to explain with examples why this is a bad idea, rather than using cryptic terms.
Your proposal would be to have code that looks like this:
public class Base
{
public int Item1 { get; set; }
public int Item2 { get; set; }
}
public class WithHidden : Base
{
hide Item1; // Assuming some new feature "hide" in C#
}
public class WithoutHidden : Base { }
This would then make the following code invalid:
WithHidden a = new WithHidden();
a.Item1 = 10; // Invalid - cannot access property Item1
int i = a.Item1; // Invalid - cannot access property Item1
And that would be just what you wanted. However, suppose we now have the following code:
Base withHidden = new WithHidden();
Base withoutHidden = new WithoutHidden();
SetItem1(withHidden);
SetItem1(withoutHidden);
public void SetItem1(Base base)
{
base.Item1 = 10;
}
The compiler doesn't know what runtime type the argument base in SetItem1 will be, only that it is at least of type Base (or some type derived from Base, but it can't tell which -- it may be obvious looking at the code snippet, but more complex scenarios make it practically impossible).
So the compiler will not, in a large percentage of the cases, be able to give a compiler error that Item1 is in fact inaccessible. So that leaves the possibility of a runtime check. When you try and set Item1 on an object which is in fact of type WithHidden it would throw an exception.
Now accessing any member, any property on any non-sealed class (which is most of them) may throw an exception because it was actually a derived class which hid the member. Any library which exposes any non-sealed types would have to write defensive code when accessing any member just because someone may have hidden it.
A potential solution to this is to write the feature such that only members which declare themselves hideable can be hidden. The compiler would then disallow any access to the hidden member on variables of that type (compile time), and also include runtime checks so that a FieldAccessException is thrown if it is cast to the base type and tried to be accessed from that (runtime).
But even if the C# developers did go to the huge trouble and expense of this feature (remember, features are expensive, especially in language design) defensive code still has to be written to avoid the problems of potential FieldAccessExceptions being thrown, so what advantage over reorganising your inheritance hierarchy have you gained? With the new member hiding feature there would be a huge number of potential places for bugs to creep into your application and libraries, increasing development and testing time.

What you want to do goes directly against the grain of OO, you can't 'unpublish' members as this violates the substitution principle. You have to refactor this into something else.

Vadim's response reminded me of how MS achieve this in the Framework in certain places. The general strategy is to hide the member from Intellisense using the EditorBrowsable attribute. (N.B. This only hides it if it is in another assembly) Whilst it does not stop anyone from using the attribute, and they can see it if they cast to the base type (see my previous explination) it makes it far less discoverable as it doesn't appear in Intellisense and keeps the interface of the class clean.
It should be used sparingly though, only when other options like restructuring the inheritance hierarchy would make it a lot more complex. It's a last resort rather than the first solution to think of.

If you use an interface instead of a base class for defining the property, you could implement the property explicitly. The would require an explicit cast to the interface to use the property.
public interface IMyInterface
{
string Name { get; set; }
}
public class MyClass : IMyInterface
{
string IMyInterface.Name { get; set; }
}
You can find more out here.

The only thing I can think of is to make item1 virtual in class a:
class a
{
public virtual int item1 { get; set; }
public int item2 { get; set; }
}
and then override it in class b but throw an exception in getter and setter. Also if this property is used in a visual designer you can use Browsable attribute to not display.
class b : a
{
[Browsable(false)]
public override int item1
{
get
{
throw new NotSupportedException();
}
set
{
throw new NotSupportedException();
}
}
}

First of all this is not good idea if you using some methods, that operates base class.
You can try to use obsolete argument to make users twice think to use this property.
[System.Obsolete("Do not use this property",true)]
public override YourType YourProperty { get; set; }

What you are describing is something akin to 'private inheritance' from C++, and is not available in C#.

You cant do it directly, but you could override the properties in the child class and make them readonly e.g.
class Program
{
static void Main(string[] args)
{
b obj = new b();
obj.item1 = 4;// should show an error but it doent ???
}
}
class a
{
public virtual int item1 {get; set;}
public virtual int item2 { get; set; }
}
class b : a
{
public override int item1
{
get { return base.item1; }
set { }
}
}
class c : a
{
}

You could use interfaces to hide the property. The child class would implemented an interface that didn't have the property then it wouldn't appear.
You would need two interfaces for when you want the property and when you don't, thus making it a horrible hack.

You can override it and then Add a [Browsable(false)] tag to prevent showing it in designer.
Simple:
public class a:TextBox
{
[Browsable(false)]
public override string Text
{
get { return ""; }
set { }
}
}

Changing the accessibility of a virtual member is an inheriting class is specifically prohibited by the C# language spec:
The override declaration and the overridden base method have the same
declared accessibility. In other words, an override declaration cannot
change the accessibility of the virtual method. However, if the
overridden base method is protected internal and it is declared in a
different assembly than the assembly containing the override method
then the override method’s declared accessibility must be protected.
From section 10.6.4 Override methods
The same rules which apply to overriding method also apply to properties, so going from public to private by inheriting from the base class can't be done in C#.

What you actually need are interfaces:
public interface ProvidesItem1
{
int item1 { get; set; }
}
public interface ProvidesItem2
{
int item2 { get; set; }
}
class a : ProvidesItem1, ProvidesItem2
{
public int item1 { get; set; }
public int item2 { get; set; }
}
class b : ProvidesItem1
{
public int item1 { get; set; }
}
Then just pass the interfaces around. If the classes should use a common implementation, put that in a third class and let them derive from that class aswell as implement their respective interface.

Yes, it is possible. What say you on the delegation. I will try to give an idea of what is called "delegation" in OOP with a piece of code:
public class ClassA
{
// public
public virtual int MyProperty { get; set; }
// protected
protected virtual int MyProperty2 { get; set; }
}
public class ClassB
{
protected ClassC MyClassC;
public ClassB()
{
MyClassC = new ClassC();
}
protected int MyProperty2
{
get { return MyClassC.MyProperty2; }
set { MyClassC.MyProperty2 = value; }
}
protected int MyProperty
{
get { return MyClassC.MyProperty; }
set { MyClassC.MyProperty = value; }
}
protected class ClassC : ClassA
{
public new int MyProperty2
{
get { return base.MyProperty2; }
set { base.MyProperty2 = value; }
}
public override int MyProperty
{
get { return base.MyProperty; }
set { base.MyProperty = value; }
}
}
}

namespace PropertyTest
{
class a
{
int nVal;
public virtual int PropVal
{
get
{
return nVal;
}
set
{
nVal = value;
}
}
}
class b : a
{
public new int PropVal
{
get
{
return base.PropVal;
}
}
}
class Program
{
static void Main(string[] args)
{
a objA = new a();
objA.PropVal = 1;
Console.WriteLine(objA.PropVal);
b objB = new b();
objB.PropVal = 10; // ERROR! Can't set PropVal using B class obj.
Console.Read();
}
}
}

You can user new modifer.
Sample;
public class Duck
{
public string Color{get; set;}
public void Swim() { }
}
public class DonaldDuck : Duck
{
new public void Swim()
{
/*you could call in DonaldDuck.Swim only here but not public for DonaldDuck client.*/
}
}

If you wanna hide a member from base class then you will need to add a new base class let's call it baseA and your code should be as follows:
class Program
{
static void Main(string[] args)
{
b obj = new b();
obj.item1 = 4;// should show an error but it doent ???
}
}
class baseA
{
public int item2 { get; set; }
}
class a:baseA
{
public int item1 { get; set; }
}
class b : baseA { }
class c : a { }

How can I wrap static properties of a base class so that they return a sub class object?

Say I have code out there like this:
public class Base // I cannot change this class
{
public string Something { get; private set; }
public string Otherthing { get; set; }
public static Base StaticPreSet
{
get { return new Base { Something = "Some", Otherthing = "Other"}; }
}
public static Base StaticPreSet2
{
get { return new Base { Something = "Some 2", Otherthing = "Other 2"}; }
}
}
public class SubClass : Base // I can change this class all I want.
{
public string MoreData { get; set; }
// How can I wrap the PreSets here so that they return SubClass objects?
// Something like this:
public static SubClass MyWrappedPreset
{
get
{
// Code here to call the base preset and then use it as the
// base of my SubClass instance.
}
}
}
What makes this complicated is the Something property. It has a private setter. So I can't set it in the subclass. The only way it can be set is is via the preset properties.
Is there a way to wrap the StaticPreSet property in my SubClass so that it will return an object of type SubClass?

// I cannot change this base class.
Given that you can't change the base class, there is no way to cause it to change behavior (ie: return a different class at runtime).
If you could influence the design of the base class static methods, you could redesign it in a way to be flexible enough to provide this functionality. However, without changing it, this won't work.
Edit in response to edit:
You could create a new static method that does what you are showing, like so:
public static SubClass MyWrappedPreset
{
get
{
// Code here to call the base preset and then use it as the
// base of my SubClass instance.
Base baseInstance = Base.StaticPreSet;
SubClass sc = new SubClass(baseInstance); // Create a new instance from your base class
return sc;
}
}
However, this provides a completely new, unrelated property - you'd have to access it via SubClass.MyWrappedPreset, not the Base class.

Static fields in a class "have nothing to do with it".
Basically, except access to private static fields, id doesn't matter in which class you put them - they behave the same.
If you inherit a class, and you declare another static field with the same name of a static field on the base class, you will simply 'hide' it. Example for you:
using System;
public class Base // I cannot change this class
{
public string Something { get; set; }
public string Otherthing { get; set; }
public static Base StaticPreSet
{
get { return new Base { Something = "Some", Otherthing = "Other"}; }
}
public static Base StaticPreSet2
{
get { return new Base { Something = "Some 2", Otherthing = "Other 2"}; }
}
}
public class SubClass : Base // I can change this class all I want.
{
public string MoreData { get; set; }
public static SubClass StaticPreSet2
{
get { return new SubClass { Something = "inherited", Otherthing=""}; }
}
}
public class Test
{
public static void Main()
{
Console.WriteLine(SubClass.StaticPreSet2.Something);
}
}
Will write "inherited".