Not sure if it is not logical but want to learn. If we don't declare our base class when creating a new class, both visual studio and compiler knows it inherits "object". is there any way to tell the compiler and visual studio(for intellisense) that my base class is not "object", it is "myobject" for example? maybe any configuration on visual studio?
you can say "inherit all your classes from 'myobject'", i know it but just want to know is it possible.
No, absolutely not. This is part of the C# spec, and is in no way optional. From section 10.1.4.1:
If a class declaration has no class-base, or if the class-base lists only interface types, the direct base class is assumed to be object.
No implementation-specific wiggle-room - that's just the way it is. Personally I'm glad - I want to be able to tell the direct base class just from looking at the source code, without knowing any project configuration.
EDIT: Just to be clear, C# could have been designed such that a different type could be specified as the base type. For example, I could imagine (but dislike) a language where:
class Foo
{
}
compiled with:
csc /evil:DefaultBaseClass=System.IO.Stream Foo.cs
was equivalent to:
class Foo : Stream
{
}
That doesn't break .NET at all - it's a purely language decision. What is enforced by .NET is that most types end up with at least an indirect base class of System.Object. I don't think a language could be designed to allow you to set up a "parallel" type hierarchy.
That's not possible, the way C# is designed, (almost) everything derives from Object. If this were not the case you couldn't rely on the methods Object provides being there, which are pretty fundamental/useful.
Note that it is .Net that requires all objects to be derived from Object (directly or indirectly). C# specifies that objects declared with no base class inherit from Object, other languages are free to specify another type, however that type must inherit (directly or indirectly) from Object as per .net requirements.
Obviously you're free to have your own base class for all types you create, however that base class has to inherit from object (either directly or indirectly).
Do you want to add methods to all/existing types? In which case use extension methods.
You could modify the existing item templates (or create a new one) so that new classes automatically inherit from some base class:
using System;
using System.Collections.Generic;
$if$ ($targetframeworkversion$ >= 3.5)using System.Linq;
$endif$using System.Text;
namespace $rootnamespace$
{
class $safeitemrootname$ : SomeBaseClass
{
}
}
See Customizing Project and Item Templates
You can create your own custom abstract class and override the 4 methods defined by the Object class and further add new virtual and abstract methods to your custom base class. Then, you can use this class as the base class explicitly for all your other custom classes. But, that will still mean the super base class of all the classes will be Object only (you can't change that). e.g.
//your custom base class
public abstract class MyObject
{
public virtual void MyCustomMethod()
{
//Your custom method implementation
}
public abstract void MyCustomAbstractMethod();
public override string ToString( )
{
//your custom implementation for override
}
public override string Equals( )
{
//your custom implementation for override
}
public override string GetHashCode( )
{
//your custom implementation for override
}
public override string GetType( )
{
//your custom implementation for override
}
}
//your custom child class
public class CustomClass1 : MyObject //still derived from object
{
//implement and override the MyObject and object methods
}
//your custom child class
public class CustomClass2 : MyObject //still derived from object
{
//implement and override the MyObject and object methods
}
But all the built-in types provided by the .Net BCL will not be able to use your MyObject class, they still will be known to be derived from object.
Ok one thing: In C# and Java all classes declared are derived automatically from Object. There is no changing this. Object is the root of the class hierarchy. Now, you can have your classes inherit another class like:
public class A : B // A inherits B
but up the chain, you will still find Object at the top because anyway B inherited Object.
i think every thing in .NET inherites from object class. 4 example, becouse it, every object have ToString() method.
All the classes and struct inheret from Object, it is the parent of all, even you inherited from a class
public class A : B // A inherits B
Related
For example, say I wanted to create a class that inherits System.Diagnostics.StopWatch, and for this example pretend that System.Diagnostics.Stopwatch.StartNew() is the only public constructor for that class (I know its not, but I'm trying to inherit a different class where that is the case) :
public class Example : System.Diagnostics.Stopwatch
{
public Example()
{
// ... return System.Diagnostics.Stopwatch.StartNew();
}
}
I know there are obvious workarounds, but just wondering if this is possible in C#
There are basically three scenarios where you can't inherit from a class:
The intended parent class is declared as sealed, which prohibits inheriting from it.
The intended parent class doesn't have an accessible constructor.
The intended parent class is a static class.
If you are in one of these 3 scenarios, you will not be able to inherit from that class, plain and simple, don't look for a usable workaround because there isn't.
I have two sequences of objects 'A' and 'B'. Comparing the sequences should produce a third sequence 'C' of elements that indicate whether:
the objects were "deleted" from 'A' or
"inserted" from 'B'.
All remaining elements are considered as "matched".
What I would like to do:
Declare Inserted<T>, Deleted<T>, and Matched<T> generic classes that inherit all their properties from the T base class. The generic class must be able to instantiate itself from the object it inherits.
The code:
public interface IInstantiable<T>
{
void CopyFrom(T o);
}
[Serializable]
public class Inserted<T> : T
where T : IInstantiable<T>
{
public Inserted() { }
public Inserted(T t)
{
this.CopyFrom(t);
}
}
The error:
'MyNamespace.Inserted<T>' does not contain a definition for 'CopyFrom' and no
extension method 'CopyFrom' accepting a first argument of type 'MyNamespace.Inserted<T>'
could be found (are you missing a using directive or an assembly reference?)
Further discussion:
I define my own IInstantiable interface to enforce the existence of a CopyFrom method. I cannot use the standard ICloneable interface, because it only defines a method that copies the object to a new instance, whereas I need the object to copy its members in the constructor.
The error goes away if the generic defines its own implementation of the CopyFrom method; however, this does not achieve the desired goal of specializing the CopyFrom method to handle the specific needs of the base class. Only the base class could know what properties should be copied. (Or am I missing something?)
Note: The final object should have the same public members as its base class, as the object should be capable of serialization.
Is this possible in .NET?
The answer:
What I am attempting to do is impossible, simply because the generic class cannot be an extension of the template base class. Visual Studio complains "Cannot derive from 'T' because it is a type parameter." (I hadn't noticed this error yet because I had not implemented the CopyFrom method in the generic class yet.)
If I were to change the interface into a class and supply a stub implementation in that class, I could inherit from it as suggested below; however, this introduces a new base class into my inheritance hierarchy.
public class IInstantiable<T>
{
public virtual void CopyFrom(T o) { }
}
[Serializable]
public class Inserted<T> : IInstantiable<T>
where T : IInstantiable<T>
{
public Inserted() { }
public Inserted(T t)
{
base.CopyFrom(t);
}
}
Unfortunately, I cannot use this new base class in its templatized form because I must introduce it at the root of my inheritance hierarchy. It works only if I remove the template and make it as generic as possible.
public class IInstantiable
{
public virtual void CopyFrom(Object o) { }
}
However, this still does not make my Inserted<T> generic look like the object it is initialized from, and since I cannot inherit from the same type as the type parameter, it does not suit my initial purpose.
Moving away from "fancy generics" based on the type system to more (ahem) generic annotated structures might prove to be the best solution; however, the default behavior of my selected serialization approach (XmlSerialization) does not have the automatic support that would make this configuration a viable solution. Generics will not work; use hard-coded class definitions instead.
This is indirectly what you're trying to declare in your code above.
[Serializable]
public class Inserted<T> : IInstantiable<T>
where T : IInstantiable<T>
{
public Inserted() { }
public Inserted(T t)
{
this.CopyFrom(t);
}
}
Does this make sense?
.NET doesn't allow you to inherit from a generic parameter. How could it? Generics are evaluated at runtime but it needs to know what type your class is at compile time.
If I understand correctly, you want to annotate a sequence of objects with the notion of what their state is (inserted, deleted, or matched).
You don't really need fancy generics for this; what's wrong with:
enum ChangeState { Inserted, Deleted, Matched }
struct<T> Annotated {
public T Obj;
public ChangeState;
}
You can mark this for serialization however you want (the Annotated object can serialize just fine without the same properties/fields).
Though you can encode more information in the type system, it's unclear to me what the benefit would be here. Are you sure you want to do that?
As stated above, is it redundant to inherit from Object in c#?
Do both sets of code below result in equivalent objects being defined?
class TestClassUno : Object
{
// Stuff
}
vs.
class TestClassDos
{
// Stuff
}
I snooped around on MSDN but wasn't able to find anything perfectly conclusive.
If left unspecified every class definition will implicitly inherit from System.Object hence the two definitions are equivalent.
The only time these two would be different is if someone actually defined another Object type in the same namespace. In this case the local definition of Object would take precedence and change the inheritance object
namespace Example {
class Object { }
class C : Object { }
}
Very much a corner case but wouldn't point it out if I hadn't seen it before
Note that the same is not true if you used object instead of Object. The C# keyword object is a type alias for System.Object and hence it wouldn't match Example.Object.
namespace Example2 {
class Object { }
class C : Object { } // Uses Example.Object
class D : object { } // Uses System.Object
}
Of course if you have a truly evil developer you could still cause confusion with object
namespace System {
class Object {
private Object() { }
}
}
namespace Example3 {
// This will properly fail to compile since it can't bind to the private
// Object constructor. This demonstrates that we are using our definition
// of Object instead of mscorlib's
class C : object { } // Uses our System.Object
}
Yes, everything ultimately inherits from an object if defined as class. Leave the explicit inheritance out of your code.
Yes it is redundant to inherit from object in class
MSDN : Object class : Supports all classes in the .NET Framework class hierarchy and provides low-level services to derived classes. This is the ultimate base class of all classes in the .NET Framework; it is the root of the type hierarchy.
Check this research : inherits from object? An investigation into how.
Object is the mother of all classes in .Net. There is nothing above it.
All classes inherit from it. So this code
class TestClassDos
{
// Stuff
}
automatically means it is inheriting from object.
Proof: You can typecast any entity to object which is possible if it is inheriting from it.
Summary of Object class says
// Supports all classes in the .NET Framework class hierarchy and provides low-level
// services to derived classes. This is the ultimate base class of all classes
// in the .NET Framework; it is the root of the type hierarchy.
Yes, they are both the same thing, I don't think I saw anyone mention structs, but all objects (that is regardless if you declare a class or a struct) they all ultimately inherit from Object, see this Object MSDN article and this other article on Structs
There is a time when inheriting from object makes sense — when you have a partial class definition, and you want to lock down inheritance and prevent other partial declarations from extending a different class. Attempting to inherit from another type in the partial class will then give you the CS0263 Compiler Error.
This only makes sense in the event that your partial class is not already inheriting from another type.
The partial keyword is not in your code example, but I thought it might be worth mentioning as I found my way here from Google after seeing a similar setup in an API. Aside from inheriting from objects that don't point to the official System.Object as others pointed out, there is no benefit in doing so as all classes inherit from object implicitly.
I had created a base class that has many public properties and were been used perfectly. Now i want to use this class to derive other class , but i do'nt want some of its properties to be exposed outside the derived class that inherits it. Is there any way that the properties of base class that are public cannot be exposed outside its derived class.(The properties that are to be hidden are public because they are used in other classes that inherits it).Any help will be highly appericiated.
You want to make them protected.
From MSDN:
A protected member is accessible within its class and by derived class instances.
I agree with cadrell0 about marking them protected, but just in case you are looking for a solution where the properties are actually public, but hidden to users of a certain derived class, you can use an explicit interface
interface IHaveMethodsYouCanHide { void Foo(); }
class Base : IHaveMethodsYouCanHide { public void Foo() {} }
class NonHidingDerived : Base { }
class HidingDerived : Base, IHaveMethodsYouCanHide
{
void IHaveMethodsYouCanHide.Foo() {}
}
With this code, identifers of type HidingDerived will not allow calls to Foo (unless first cast to IHaveMethodsYouCanHide).
What you're asking for is simply not possible. If type B inherits from type A then it "is-a" type A. B has at least the same accessible contract that type A had. There is no way to hide a public member of A without fundamentally violating this contract.
If you find yourself in a scenario where you want to use A but only expose a subset of the properties then inheritance is not the right solution: containment is the proper solution.
public class B {
private A m_wrapped;
// Expose only the properties you want to expose here
}
I am sorry if I am asking something stupid but I am completely a newbie in C# and ASP.NET.
I am having an error in my code and I don't understand it.
I am working on Visual Studio 2008.
In this line of code:
public class SQLFAQProvider : DBFAQProvider
I am getting this error:
Moby.Commerce.DataAccess.FAQ.SQLFAQProvider does not implement inherited abstract member Moby.Commerce.DataAccess.FAQDBFAQProvider.DeleteFAQbyID(int)
When I go to DBFAQProvider the error is in this line of code:
public abstract DBFAQ DeleteFAQbyID(int fAQID);
What should I change to correct it?
First thought would be implement the abstract member in the inherited class ala:
public class SQLFAQProvider : DBFAQProvider
{
public override DBFAQ DeleteFAQbyID(int fAQID)
{
//TODO: Real Code
return null;
}
}
Implement the DeleteFAQbyID method in your derived class:
public override DBFAQ DeleteFAQbyID(int fAQID)
{
// Put your code here
}
The point of an abstract method is to say (in the abstract base class), "I want to make sure that this method is available in every concrete class deriving from me" - it's up to you to provide the implementation. It's a bit like a method in an interface.
Your subclass needs to explicitly implement that particular method.
If you have no idea how to do it, then at least do:
public override DBFAQ DeleteFAQbyID(int fAQID)
{
throw new NotImplementedException("This isn't done yet");
}
When you inherit from a class in C#, you are required to implement all methods marked as abstract unless your class is itself marked as abstract. Abstract classes are ones that cannot be directly instantiated at runtime because they don't fully implement all of the required methods that the base class(es) say must exist.
Abstract methods are a mechanism that allows a class to indicate that a particular method must "eventually" exist - without having to provide an implementation at that point. You typically use abstract classes when you cannot or don't want to dictate what a particular implementation should do, but you need to pre-define a method that you will eventually rely on.
To fix your problem either mark your class as abstract (with the expectation that another level of inheritance will fill in the missing pieces) or implement DeleteFAQbyId() in your class:
public DBFAQ DeleteFAQbyID(int fAQID)
{
// write appropriate implementation here or:
throw new NotImplementedException();
// or possibly NotSupportedException() if the operation should can't ever be supported.
}
When a class inherits from an abstract class it must implement all abstract methods defined by said class. This is the class interface, the abstract methods can be thought of as pure virtual functions, i.e., functions that must be implemented by descended classes but do not make sense to be implemented in the base class.
Because your SQLFAQProvider class isn't abstract, it has to implement every abstract method that it inherits.
To fix this, implement the DeleteFAQbyID method in SQLFAQProvider, like this:
public override DBFAQ DeleteFAQbyID(int fAQID) {
//Do something
}
Alternatively, you could make your SQLFAQProvider class abstract by changing its declaration to public abstract class SQLFAQProvider.
Your subclass (SQLFAQProvider) must provide implementation code for the method DeleteFAQbyID because the parent class (DBFAQProvider) did not.
In the abstract class use an entity property like IsValid. Make it return the abstract method that you want to override in the derived class.
In abstract base class:
public bool IsValid
{
get
{
return DeleteFAQbyID();
}
}
public abstract bool DeleteFAQbyID();
In the derived class now it will override the abstract class' method.