What is the proper way to implement an interface that has its own interface members? (am I saying that correctly?) Here's what I mean:
public Interface IFoo
{
string Forty { get; set; }
string Two { get; set; }
}
public Interface IBar
{
// other stuff...
IFoo Answer { get; set; }
}
public class Foo : IFoo
{
public string Forty { get; set; }
public string Two { get; set; }
}
public class Bar : IBar
{
// other stuff
public Foo Answer { get; set; } //why doesnt' this work?
}
I've gotten around my problem using explicit interface implementation, but I'm wondering if there is a better way?
You need to use the exact same type as in the interface:
public class Bar : IBar
{
public IFoo Answer { get; set; }
}
Note: IFoo instead of Foo.
The reason is that the interface defines a contract and the contract says that it must be an IFoo.
Think about it:
You have the classes Foo and Foo2, both implement IFoo. According to the contract, instances of both classes can be assigned. Now, if your code was legal, this would somehow break because your class only accepts Foo. Explicit interface implementation doesn't change that fact in any way.
You'll need to use generics to be able to do what you want.
public interface IFoo
{
string Forty { get; set; }
string Two { get; set; }
}
public interface IBar<T>
where T : IFoo
{
// other stuff...
T Answer { get; set; }
}
public class Foo : IFoo
{
public string Forty { get; set; }
public string Two { get; set; }
}
public class Bar : IBar<Foo>
{
// other stuff
public Foo Answer { get; set; }
}
This will allow you to provide an interface that says something like, "to implement this interface you must have a property with a public getter/setter of a type that implements IFoo." Without generics you are simply saying that the class has a property with a type of exactly IFoo, rather than anything that implements IFoo.
IBar has a IFoo field, not a Foo one, do this instead:
public class Bar : IBar
{
// other stuff
public IFoo Answer { get; set; }
}
Foo may extend type IFoo but that isn't what the interface exposes.
An interface defines a contract and you need to obey the terms of that contract.
So the correct way is to use
public IFoo Answer{get;set;} like others have said.
Related
I have a rather simple problem, but I can't find a proper solution anywhere. I would like to specify an abstract object CustomValues as property in my abstract parent class. However, the class inheriting from it should be able to use a more specific type as an object for this property CustomValues. At first I thought I would solve the problem by an interface, but unfortunately that didn't work out either. How do you do something like that, that it works?
public abstract class MyAbstract {
public abstract object CustomValues { get; set; }
}
public class MyImplementation : MyAbstract {
public override MySpecificClass CustomValues { get; set; }
}
This will throw me three errors:
Missing implementation for getter
Missing implementation for setter
Type missmatch between type object and MySpecificClass
The solution suggested in the comments would look something like this. (I'm assuming CustomValues should be a collection of something.)
public class MyClass<T>
{
public ICollection<T> CustomValues { get; set; }
}
Or to ensure CustomValues itself cannot be reassigned, but can be accessed and added to:
public class MyClass<T>
{
public ICollection<T> CustomValues { get; } = new List<T>();
}
I think your original thought that use an interface (+ generic) was at the correct direction. In general you might want to add type constraints as well.
public interface ICustomValues {
....
}
public class MySpecificClass : ICustomValues {
....
}
public abstract class MyAbstract<T> where T : ICustomValues {
public abstract T CustomValues {
get;
set;
}
}
public class MyImplementation: MyAbstract<MySpecificClass> {
public override MySpecificClass CustomValues { get; set; }
}
Thanks to you all guys. I found the solution by using a generic properly:
public abstract class MyAbstract<T> {
public abstract T CustomValues { get; set; }
}
public class MyImplementation : MyAbstract<MySpecificClass> {
public override MySpecificClass CustomValues { get; set; }
}
I have one class with a generic type, like this:
public class Test<T> {
/*
Some Properties and Fields
*/
}
Now I need a public Property SubTest{T} in class Test{T} with datatype Test{T}
public class Test<T> {
/*
Some Properties and Fields
*/
public Test<T> SubTest { get; set; }
}
T and U are not the same datatype and SubTest can be null.
Is that possible in C#?
Update
Or like This?
public class Test {
/*
Some Properties and Fields
*/
public Type ElementType { get; private set; }
public Test SubTest { get; set; }
public Test(Type elementType) {
ElementType = elementType;
}
}
U it not defined so it cannot be used like the. You need to create type parameter in the class, or use a specific type, for example string:
public class Test<T, U> {
/*
Some Properties and Fields
*/
public Test<T,U> SubTest { get; set; }
}
Your question is a bit inconsistent:
Now I need a public Property SubTest{T} in class Test{T} with datatype
Test{T}
But your example is different, and now U has been added.
public class Test<T>
{
public Test<U> SubTest { get; set; }
}
So to answer your question as-is, replace U with T:
public class Test<T>
{
public Test<T> SubTest { get; set; }
}
I think what you are trying to do is to create a generic "test" object, and then have multiple implementations (with different types). I would use interfaces instead, but its the same concept with classes.
public interface ITest
{
// general test stuff
}
// Type-specific stuff
public interface ITesty<T> : ITest
{
public ITest SubTest { get; set; } // a sub-test of any type
}
I'm changing a class from public abstract AwesomeClass, to public sealed AwesomeClass. I've also added a new property. All existing members are unchanged. I know that this is a breaking change. Clients that have implemented AwesomeClass or relied on it being abstract via reflection will be broken.
My question is, will clients that have only used members of instances of AwesomeClass that I've provided, be broken (and if yes how)? None of the clients will have a dependency on any of my types that implemented AwesomeClass as they were all internal. I think not, but...
Here is the class before and after:
public abstract class AwesomeClass
{
public abstract Guid SuperGuid { get; set; }
public abstract int SuperInt { get; set; }
}
public sealed class AwesomeClass
{
public Guid SuperGuid { get; set; }
public int SuperInt { get; set; }
public int OtherSuperInt { get; set; }
}
You mean that when you have this:
public abstract class Foo
{
public string Bar;
}
void UpdateFooBar(Foo foo)
{
foo.Bar = "Updated";
}
And you change abstract class Foo to sealed class Foo, will UpdateFooBar(Foo foo) continue to work?
What kept you from trying? But yes, it will.
Can I make some properties public only to same interface classes and readonly to all other classes?
You can use explicit implementation, for example:
interface IFoo {
int Value { get; set; }
}
public class Foo : IFoo {
public int Value { get; private set; }
int IFoo.Value {
get { return Value; }
set { Value = value; }
}
}
When accessed via Foo only the get will be accessible; when accessed via IFoo both getter and setter will be accessible.
Any use?
An interface is just something like a contract for classes. It doesn't change the accessibility level.
If a member of a class is public it is public to all classes that can access the class. The only restrictions you can have is the use of internal or protected. internal makes the member public to classes which are defined within the same assembly and protected makes it public to classes derived from the class.
Instead of the interface you can create an abstract base class and make the members protected:
public interface IFoo
{
int Value { get; set; }
}
public abstract class FooBase : IFoo
{
public abstract int Value { get; set; }
protected void ProtectedMethod()
{
}
}
public class Foo : FooBase
{
public int Value { get; set; }
}
However you can not define a member that is accessible by classes that implement a specific interface. There is no access modifier like public-to-IFoo-otherwise-private.
I have an object that implements two interfaces... The interfaces are:
public interface IObject
{
string Name { get; }
string Class { get; }
IEnumerable<IObjectProperty> Properties { get; }
}
public interface ITreeNode<T>
{
T Parent { get; }
IEnumerable<T> Children { get; }
}
such that
public class ObjectNode : IObject, ITreeNode<IObject>
{
public string Class { get; private set; }
public string Name { get; private set; }
public IEnumerable<IObjectProperty> Properties { get; set; }
public IEnumerable<IObject> Children { get; private set; }
public IObject Parent { get; private set; }
}
Now i have a function which needs one of its parameters to implement both of these interfaces. How would i go about specifying that in C#?
An example would be
public TypedObject(ITreeNode<IObject> baseObject, IEnumerable<IType> types, ITreeNode<IObject>, IObject parent)
{
//Construct here
}
Or is the problem that my design is wrong and i should be implementing both those interfaces on one interface somehow
public void Foo<T>(T myParam)
where T : IObject, ITreeNode<IObject>
{
// whatever
}
In C#, interfaces can themselves inherit from one or more other interfaces. So one solution would be to define an interface, say IObjectTreeNode<T> that derives from both IObject and ITreeNode<T>.
It's probably easiest to define an interface that implements both IObject and ITreeNode.
public interface IObjectNode<T> : IObject, ITreeNode<T>
{
}
Another option, in case you don't expect the above interface would be used often, is to make the method/function in question generic.
public void Foo<T>(T objectNode) where T : IObject, ITreeNode<IObject>
public void MethodName<TParam1, TParam2>(TParam1 param1, TParam2 param2)
where TParam1 : IObject
where TParam2 : ITreeNode<IObject>