I'm trying to create an abstract class that defines a property with a getter. I want to leave it up to derived classes to decide if they want to implement a setter for the property or not. Is this possible?
What I have so far:
public abstract class AbstractClass {
public abstract string Value { get; }
public void DoSomething() {
Console.WriteLine(Value);
}
}
public class ConcreteClass1 : AbstractClass {
public override string Value { get; set; }
}
public class ConcreteClass2 : AbstractClass {
private string _value;
public override string Value {
get { return _value; }
}
public string Value {
set { _value = value; }
}
}
public class ConcreteClass3 : AbstractClass {
private string _value;
public override string Value {
get { return _value; }
}
public void set_Value(string value) {
_value = value;
}
}
In ConcreteClass1, I get an error on the set. It can't override set_Value because no overridable set accessor exists in AbstractClass.
In ConcreteClass2, I get an error on both Value's because a member with the same name is already declared.
ConcreteClass3 doesn't give an error, but even though Value's set accessor would be compiled into set_Value, it doesn't work the other way around. Defining a set_Value does not mean that Value gets a set accessor. So I can't assign a value to a ConcreteClass3.Value property. I can use ConcreteClass3.set_Value("value"), but that's not what I'm trying to achieve here.
Is it possible to have the abstract class demand a public getter, while allowing an optional setter to be defined in a derived class?
In case you'r wondering, this is just a theoretical question. I don't have a real situation where something like this is needed. But I can imagine an abstract class that doesn't care how a property gets set, but that does need to be able to get the property.
Unfortunately, you can't do exactly what you want. You can do this with interfaces though:
public interface IInterface {
string MyProperty { get; }
}
public class Class : IInterface {
public string MyProperty { get; set; }
}
The way I would do it is to have a separate SetProperty method in the concrete classes:
public abstract class AbstractClass {
public abstract string Value { get; }
}
public class ConcreteClass : AbstractClass {
private string m_Value;
public override string Value {
get { return m_Value; }
}
public void SetValue(string value) {
m_Value = value;
}
}
Found a solution: How to override a getter-only property with a setter in C#?
public abstract class A
{
public abstract int X { get; }
}
public class B : A
{
public override int X { get { return 0; } }
}
/*public class C : B //won't compile: can't override with setter
{
private int _x;
public override int X { get { return _x; } set { _x = value; } }
}*/
public abstract class C : B //abstract intermediate layer
{
public sealed override int X { get { return this.XGetter; } }
protected abstract int XGetter { get; }
}
public class D : C //does same thing, but will compile
{
private int _x;
protected sealed override int XGetter { get { return this.X; } }
public new virtual int X { get { return this._x; } set { this._x = value; } }
}
D is now equivalent to a class inheriting from B while also being able to override in a setter.
You can just use protected access modifier instead. Because of inheritance you are not allowed to use private. It looks like so:
public abstract class A
{
public abstract int prop { get; protected set; }
}
public abstract class B : A
{
public override int prop { get; protected set; }
}
Not very elegant, but it's the closest you can get without doing something like you have in concreteclass3
public class Concrete : AbstractClass
{
public new void DoSomething()
{
Console.WriteLine(Value);
}
}
public abstract class AbstractClass
{
protected AbstractClass()
{
try
{
var value = Value;
}
catch (NotImplementedException)
{
throw new Exception("Value's getter must be overriden in base class");
}
}
public void DoSomething()
{
Console.WriteLine(Value);
}
/// <summary>
/// Must be override in subclass
/// </summary>
public string Value { get { throw new NotImplementedException(); } }
}
Related
I'm trying to have an interface which declares that a property must have a get:
public interface IValue {
public int Value { get; }
}
And then have an abstract class also define it, but keep it abstract:
public abstract class BaseClass : IValue {
public abstract int Value { get; }
}
And then I want to allow a subclass to define the getter and add a setter:
public class SubClass : BaseClass {
public int Value { get; set; }
}
I get an error like:
'SubClass.Value' hides inherited member `BaseClass.Value'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword
If I try:
public class SubClass : BaseClass {
public override int Value { get; set; }
}
I get:
`SubClass.Value.set': cannot override because `BaseClass.Value' does not have an overridable set accessor
Is there any way to allow a subclass to optionally add a setter when inheriting from an abstract class that only defines a getter?
Update: Just to clarify, I know of the workarounds I can do. My goal was to see what's the cleanest way I can do this. The reason I don't just throw a public setter on BaseClass is because some subclasses of BaseClass may not have a public setter. The end goal is basically just provide a common Value getter for the times they're used commonly.
You can't override getter, and add new setter.
This is what your code is, when properties are compiled into get_Value and set_Value methods:
public interface IValue
{
int get_Value();
}
public abstract class BaseClass : IValue
{
public abstract int get_Value();
}
public class SubClass : BaseClass
{
public override int get_Value() { /* ... */ }
// there's no set_Value method to override in base class
public override void set_Value(int value) { /* ... */ }
}
There are at least three ways:
define new int Value property in SubClass (note, then there's a difference);
override Value property and add SetValue method in SubClass;
define setter in BaseClass and override property.
'SubClass.Value' hides inherited member 'BaseClass.Value'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword
Is a warning not an error. It just says that you have public int Value in both abstract and concrete classes. Your abstract class has implementation of this property so when you declare it again in concrete class you just replace it with new property. So compiler advice you to use 'new' word for that purpose.
To use public override int Value { get; set; } you have to mark it 'virtual' in base class. Only virtual members can be overriden.
Class A { public virtual int Value { get; set; } }
Class B : A { public override int Value { get; set; } }
P.S. Interface members are public and abstract by default. So if you declare getter and setter in interface - you have to implement it in a concrete class.
Try to use this code:
public interface IValue
{
int Value { get; set; }
}
public abstract class BaseClass
{
int value;
int Value { get { return value; } }
}
public class SubClass : BaseClass, IValue
{
public int Value { get { return Value; } set { this.Value = value; } }
}
It appears there simply isn't a way to add the set with an abstract class in the middle without declaring a setter up-front. I've tried a ton of different combinations, and no luck.
Finally, I ended up doing this, which isn't ideal, but at least lets me not have a setter everywhere.
public interface IValue {
public int Value { get; }
}
public abstract class BaseClass : IValue {
public abstract int Value { get; }
}
public class SubClass : BaseClass {
protected int val;
public int Value { get { return val; } }
public int SetValue (int value) { val = value; }
}
public class SubClassWithoutSetter : BaseClass {
public int Value { get { return 50; } }
}
Basically, just do a "classic" setter, since there doesn't seem to be a syntax that supports letting me add a setter property after the fact.
It'd be nice if C# would implement something like:
public int Value { override get; set; } // note: this does not work
I have this class
class A
{
public string OnlyOnA { get; private set; }
public virtual void Accept<T>(ITaker<T> ia) where T : A
{
ia.Take((T)this);
}
}
and this interface
interface ITaker<T> where T : A
{
void Take(T a);
}
with this I can subclass A like following
class B : A
{
public string OnlyOnB { get; private set; }
}
and implement the interface
class BTaker : ITaker<B>
{
public void Take(B b)
{
var v = b.OnlyOnB;
}
}
I get the flexibilty in the Taker class to get the correct type of A and subtypes of A.
but I still need to the cast in A where I have to do (T)this;
how can I avoid the cast?
many thanks.
What you are trying to do is unsafe since you can do:
new A().Accept(new BTaker());
To make this safe you could create a new interface to specify the type of T which can be accepted e.g.
interface IAccept<T> where T : A
{
void Accept(ITaker<T> taker);
}
class A : IAccept<A>
{
public string OnlyOnA { get; private set; }
public virtual void Accept(ITaker<A> ia)
{
ia.Take(this);
}
}
If i have a ClassA
public class ClassA
{
public string name;
}
Where Attribute Name is Public ,and it can be modified from Anywhere .
Than i have a ClassB
public class ClassB : ClassA
{
private string name;//But it's not Woking ,name is still public
}
...which Inherit's ClassA ,but i need at ClassB to make name as Private Field.
So if i create an Object of Type ClassB than ClassB.name cannot be modified .
just don't publish the field but accessors:
public class ClassA
{
private string _name;
public string Name { get { return _name; } protected set { _name = value; } }
}
public class ClassB : ClassA
{
/* nothing left to do - you can set Name in here but not from outside */
}
This is not possible. You can not change visibility of base class's field.
Assuming you cannot change A, do not use inheritance, but aggregation and delegation:
public class A {
public string name;
public int f() { return 42; }
}
public class B {
private A a;
public int f() { return a.f(); }
public string getName() { return a.name; }
}
Carsten Konig's method is a good way, and here is an alternative.
public class ClassA {
public virtual string Name {
get;
private set;
}
}
public class ClassB : ClassA {
public override string Name {
get {
return base.Name;
}
}
}
Hm. There is a pair of tricks for this. But none of them is what you really want. One is:
public class ClassA
{
protected string name;
public string Name { get { return name; } public set { name = value; } }
}
public class ClassB : ClassA
{
public new string Name { get { return base.name; } }
}
If you don't have control over ClassA, you can do this:
void Main()
{
var b = new ClassB();
var a = (ClassA)b;
a.name = "hello";
b.PrintName();
}
class ClassA {
public string name;
}
class ClassB : ClassA {
private new string name;
public void PrintName() {
Console.WriteLine(base.name);
}
}
Assuming I have:
public abstract class A {
public abstract string Name { get; }
}
I want to use the "shortcut" for creating properties in the child class:
public string Name { get; set; }
Instead of:
private string _Name;
public string Name {
get{ return _Name; }
set{ _Name=Name; }
}
But this cause compilation error since I have set; there
public class B {
public override Name{get; set;}
}
How can I override only get;?
Just implement the getter:
public override string Name
{
get
{
return this.name;
}
}
private string name;
The shorthand for a simple get + set property is great if you want a simple get + set property, but if you want something more complicated (such as a property with just a getter) you need to implement it yourself.
Short answer: there is no shorthand way
public class B {
private string iName;
public override string Name{get{ return iName;}}
}
on a side note:
You could make your base class an interface and then override in the implementing class:
public interface A {
string Name { get; }
}
public class B : A {
public string Name {get;set;}
}
I am fairly new to inheritance and wanted to ask something. I have a base class that has lots of functionality that is shared by a number of derived classes.
The only difference for each derived class is a single method called Name. The functionality is the same for each derived class, but there is a need for the Name distinction.
I have a property in the base class called Name. How do I arrange it so that the derived classes can each override the base class property?
Thanks.
Declare your method as virtual
public class A
{
public virtual string Name(string name)
{
return name;
}
}
public class B : A
{
public override string Name(string name)
{
return base.Name(name); // calling A's method
}
}
public class C : A
{
public override string Name(string name)
{
return "1+1";
}
}
Use a virtual property:
class Base
{
public virtual string Foo
{
get;
set;
}
}
class Derived : Base
{
public override string Foo
{
get {
// Return something else...
}
set {
// Do something else...
}
}
}
You can declare it with a virtual or abstract keyword in the base class, then the derived class can over-ride it
you need to declare your property (in the base clase) as virtual
To enable each derived class to override the property you just need to mark the property as virtual
class Base {
public virtual Property1 {
get { ... }
set { ... }
}
}
Well I'm not sure from your description that inheritance is actually the right solution to the problem but here's how you make it possible for a property to be overridden:
class Base
{
public virtual string Name { get; set; }
}
But do you need it to be writable? A readonly property may make more sense in which case this might work:
class Base
{
public virtual string Name
{
get { return "BaseName"; }
}
}
class Derived : Base
{
public override string Name
{
get { return "Derived"; }
}
}
In the base class:
public virtual string Name { get; set; }
In the derived classes:
public override string Name { get; set; }
However, if the only difference between the classes is that they have different names, I'd argue that instead of inheritance you should just use the base class with the Name set in the constructor:
e.g.
public class MyObject
{
public string Name { get; private set; }
public enum ObjectType { TypeA, TypeB, ... }
public MyObject(ObjectType obType)
{
switch (obType)
{
case ObjectType.TypeA:
Name = "Type A";
// and so on
}
}
}