I have the following class:
public class DataInterop <T> where T : ITableAdapter
{
private ITableAdapter tableAdapter;
public DataInterop(T tableAdapter)
{
this.tableAdapter = tableAdapter;
}
}
In the ITableAdapter-Interface are Methods defined like Read(), Write(...), Update(...), Delete(...), ...
Now I want the Class DataInterop to have all Methods from the ITableAdapter interface.
Is it possible for a generic-class to inherit from an interface?
You just need to add : ITableAdaper after the DataInterop<T>
public class DataInterop<T>: ITableAdapter where T: ITableAdapter
{
private ITableAdapter tableAdapter;
public DataInterop(T tableAdapter)
{
this.tableAdapter = tableAdapter;
}
}
(It looks like you're implementing an Adapter Pattern or a Decorator Pattern.)
Yes it is possible, it's especially useful when you handle instances of the class without knowing the concrete type at runtime.
The syntax would be:
public class DataInterop <T> : ITableAdapter where T : ITableAdapter
Ofcourse you can. Sample layout -
public interface IBar
{
string Name { get; set; }
}
public class Foo<T> : IBar
{
public string Name { get; set; }
}
Related
How do I force all derived classes of an interface to have a constructor with a signature? This doesn't work:
public interface Constructor<T> where T : Constructor<T>, new()
{
Constructor(T);
}
public interface IParameters
{
}
public interface IRule : Constructor<IParameters>
{
//IRule (IParameters); must exist
}
You can't, not via an interface. But you can sort of get at it with an abstract class. Similar to what the accepted answer here describes, try:
public abstract class MustInitialize<T>
{
public MustInitialize(T parameters)
{
}
}
public class Rule : MustInitialize<IParameters>, IRule
{
IParameters _parameters;
public Rule(IParameters parameters)
: base (parameters)
{
_parameters= parameters;
}
}
You can't force a specific constructor signature.
Even with an abstract class as demonstrated in Mark's answer, you can only force the constructor of the abstract class, but nothing is stopping the author of the derived class to do something like this:
public class Rule : MustInitialize<IParameters>, IRule
{
public Rule()
: base (new Parameters())
{
// Assuming Parameters is a class that implements the IParameters interface
}
}
However, you can force dependency injection by using method (setter) injection:
public interface IMethodInjection<T>
{
void Method(T injected);
}
I think you can design your base class like the following example:
public abstract class MyBase
{
private MyBase()
{
}
public MyBase(string a)
{
}
}
public class MyDerived : MyBase
{
public MyDerived(string a) : base(a)
{
}
}
You can even delete the private constructor if its not needed
I'm constantly running into the problem of having an abstract class that does all the heavy lifting and then I have a lot of polymorphic classes that customize the abstract to a specific need. The abstract generally needs a lot of parameters, so they all have to be passed from all polymorphic classes
public class FooComplex : AbstractFoo {
public FooComplex(IBarAwesome awesome, IBarCool cool, ...) : base(IBarAwesome awesome, IBarCool cool, ...) { }
...a lot of overriding abstracts
}
public class FooSimple : AbstractFoo
{
public FooSimple(IBarAwesome awesome, IBarCool cool, ...) : base(IBarAwesome awesome, IBarCool cool, ...) { }
...little bit of overriding abstracts
}
public class AbstractFoo
{
public AbstractFoo(IBarAwesome awesome, IBarCool cool, ...)
...heavy lifting
}
Is there anything I can do to not pass all these things, but be able to unit test them? I've always been taught that doing
var awesome = container.Resolve<IBarAwesome>();
In like say the constructor is bad practice.
The reason I would like to find a solution to this, is it makes it harder and hard to pass anything new into the abstract class as I have to copy and pass the same parameters into many polymorphic subclasses.
I believe this is similar to what #C.Evenhuis mentioned in the comments by abstracting your constructor parameters into a common interface so they can be passed as single constructor parameter as well as being easily tested.
Concrete Classes:
public class FooComplex : AbstractFoo
{
public FooComplex(ComplexParam complexParam) : base(complexParam)
{}
}
public class FooSimple : AbstractFoo
{
public FooSimple(SimpleParam simpleParam) : base(simpleParam)
{}
}
Single Generic Concrete Class (Optional)
With this class, you could pass any type into the constructor which inherits IParams and potentially remove the need for FooComplex and FooSimple.
public class Foo<T> : AbstractFoo where T : IParam
{
public Foo(T param) : base(param)
{ }
}
Base Abstract Class:
public abstract class AbstractFoo
{
protected AbstractFoo(IParam parameter) { }
}
Interfaces:
public interface IBarCool : IBar
{}
public interface IBarAwesome : IBar
{}
public interface IBar
{}
public interface IParam
{
IEnumerable<IBar> Param { get; }
}
Reusable Concrete Parameters:
I personally don't like this method below because of the repetition but I suppose if each of the classes have their own separate implementation then it's okay. Another option would be to just have a class called ParameterHolder and two instances of the class named appropriately e.g. var complex = new ParameterHolder() and pass to the Generic Foo<T>.
public class ComplexParam : IParam
{
public IEnumerable<IBar> Param { get; }
public ComplexParam(IEnumerable<IBar> complexParam)
{
Param = complexParam;
}
}
public class SimpleParam : IParam
{
public IEnumerable<IBar> Param { get; }
public SimpleParam(IEnumerable<IBar> simpleParam)
{
Param = simpleParam;
}
}
All that needs to happen is:
public interface IAbstractParams
{
IBarAwesome awesome { get; }
IBarCool cool { get; }
...
}
public class FooComplex : AbstractFoo
{
public FooComplex(IAbstractParams params) : base(params) { }
...a lot of overriding abstracts
}
public class FooSimple : AbstractFoo
{
public FooSimple(IAbstractParams params) : base(params) { }
...little bit of overriding abstracts
}
public class AbstractFoo
{
protected readonly IBarAwesome _awesome;
protected readonly IBarCool _cool;
public AbstractFoo(IAbstractParams params)
{
_awesome = params.awesome;
_cool = params.cool;
}
...heavy lifting
}
then you need to add the nuget package Autofac.Extras.AggregateService and add this line to your builder:
builder.RegisterAggregateService<IAbstractParams>();
Thank you to #Travis Illig and #C.Evenhuis for helping me come up with this solution.
For more complex solutions to this same problem please look at #Kitson88
Using C#, how do I create instances of classes that implement a generic interface, that inherits from another generic interface using Reflection.
I need to get the implementation of BarcodeTestHelper and BarcodeRepository and create instances of them.
My model:
public interface ITestData{}
public class BarcodelData : ITestData
{
public int Id { get; set; }
}
My API:
public interface IBaseTestHelper<T> where T : ITestData {}
public interface IBarcodeTestHelper : IBaseTestHelper<BarcodeTestData>
My implementation:
public class BarcodeTestHelper : TestBaseHelper, IBarcodeTestHelper
{
private readonly IBarcodeRepository<BarcodeTestData> _barcodeRepository;
public BarcodeTestHelper(IBarcodeRepository<BarcodeTestData> barcodeRepository)
{
_barcodeRepository = barcodeRepository;
}
}
public interface IBarcodeRepository<T> : IRepository<BarcodeTestData> where T : ITestData
{
BarcodeTestData SaveBarcode(string xmlBarcode);
}
public class BarcodeRepository : IBarcodeRepository<BarcodeTestData>
{
BarcodeTestData SaveBarcode(string xmlBarcode)
{
do save work
}
}
I have this base class:
public class BaseEvent
{
public int EventID { get; set; }
public int GetEventID()
{
return EventID;
}
}
And then I have another class inherited from that base one:
public class ValidationResult<T> where T : BaseEvent
{
private void AddEventStatusUpdater(ValidationResult<T> validationResult)
{
validationResult.GetEventID();
}
}
The issue I´m having is that I cannot access the GetEventID() method from the base class.
I think this may happen because I´m using a T generic. Is there any other way to access this method?
public class ValidationResult<T> where T : BaseEvent
Says that T must be a BaseEvent, not that ValidationResult<T> inherits from BaseEvent. That'd be:
public class ValidationResult<T> : BaseEvent
And there T would not have any constraint
Is that what you want?
You have begun to implement a generic interface rather than inheriting from the base class. I think you meant to do the following:
public class ValidationResult : BaseEvent
{
private void AddEventStatusUpdater()
{
var id = this.GetEventID();
}
}
I have a generic class with a class constraint on it.
public class MyContainer<T> where T : MyBaseRow
MyBaseRow is an abstract class which I also want to contain a member of some flavour of MyContainer.
public abstract class MyBaseRow
{
public MyContainer<MyBaseRow> ParentContainer;
public MyBaseRow(MyContainer<MyBaseRow> parentContainer)
{
ParentContainer = parentContainer;
}
}
I am having problems with the constructors of classes inherited from MyBaseRow eg.
public class MyInheritedRowA : MyBaseRow
{
public MyInheritedRowA(MyContainer<MyInheritedRowA> parentContainer)
: base(parentContainer)
{ }
}
Won't allow MyInheritedRowA in the constructor, the compiler only expects and only allows MyBaseRow. I thought the generic class constraint allowed for inheritance? What am I doing wrong here and is there any way I can redesign these classes to get around this?
Many thanks in advance for any responses.
Basically, you can't use generics that way, because the covariance system doesn't work that way with classes. See here: http://geekswithblogs.net/abhijeetp/archive/2010/01/10/covariance-and-contravariance-in-c-4.0.aspx
You can however use an interface like this:
public interface MyContainer<out T> where T : MyBaseRow {
}
And that code will compile.
You can make a covariant generic interface (C#4.0):
public interface IContainer<out T> where T : MyBaseRow
{
}
public class MyContainer<T> : IContainer<T> where T : MyBaseRow
{
}
public abstract class MyBaseRow
{
public IContainer<MyBaseRow> ParentContainer;
public MyBaseRow(IContainer<MyBaseRow> parentContainer)
{
ParentContainer = parentContainer;
}
}
public class MyInheritedRowA : MyBaseRow
{
public MyInheritedRowA(IContainer<MyInheritedRowA> parentContainer)
: base(parentContainer)
{ }
}