I have a class that is generated by a third party tool:
public partial class CloudDataContext : DbContext
{
// ...SNIPPED...
public DbSet<User> Users { get; set; }
}
I create a partial class and then assign an interface so that I can inject this class later:
public partial class CloudDataContext : IDataContext
{
}
The IDataContext has the single property Users.
This won't compile, the compiler complains that the interface isn't implemented.
If I move the interface to the generated class, it works fine. I can't do that though as it's generated code.
How can I apply an interface to a partial class to expose the class as defined above?
The problem must be somewhere else, because you can implement interface in the other part of partial class than it's set on. I just tried following and it compiles just fine:
public interface IFoo
{
int Bar { get; set; }
}
public partial class Foo
{
public int Bar { get; set; }
}
public partial class Foo : IFoo
{
}
The properties probably use different types in interface and class.
Here's a quick checklist. Do the classes have identical:
Names?
Namespaces?
Access modifiers?
Example:
You decide to split an existing class into two files.
The original file's namespace doesn't match its folder path.
Consequently, the new class file you create has a mismatching namespace.
Build fails.
IN my Case problem was that interface Method that was implemented in other part of the partial class was not compiling and C# was giving error of not implemented Method
In my case, the interface method signature didn't mention a value (uint direction) that the actual method expected. This showed up as the interface having errors in one of the partial classes. Make sure that the interface for a method is actually the same as the method signature itself. D'oh.
Related
I am trying to find a way to derive a class from a generic base class. Say:
sealed public class Final : Base<Something>
{
}
public class Base<T> : T
where T : Anything // <-- Generics do not allow this
{
}
In C# this does not seem to be possible.
Is there any other solution to achieve something similar to this?
I found this StackOverflow question, but it doesn't seem to solve the issue, or at least I do not understand how it should.
EDIT:
The result I'd like to get is to be able to do something like that:
Anything[] anything;
//Assign some Instances to anything
foreach(Final final in anything){
//do something with final
}
The result I'd like to get is to be able to do something like that:
Anything[] anything;
//Assign some Instances to anything
foreach(Final final in anything){
//do something with final
}
Your foreach loop suggests this: class Anything : Final { … }.
This obviously turns around the inheritance hierarchy as you planned and named it. (You cannot have cycles in your inheritance relationships).
public class Base<T> : T where T : Anything { …
Let me elaborate on this part for a bit. I'll reduce your example even further to just class Base<T> : T.
This is not possible, for good reason. Imagine this:
class Base<T> : T
{
public override string Frobble()
{
Fiddle();
return "*" + base.Frobble() + "*";
}
}
class A
{
public sealed string Frobble() { … }
}
class B
{
}
class C
{
public virtual string Frobble() { … }
}
abstract class D
{
public abstract void Fiddle();
public virtual string Frobble() { … }
}
class E
{
public void Fiddle() { … }
public virtual string Frobble() { … }
}
You get all kinds of absurd situations if class Base<T> : T were allowed.
Base<A> would be absurd because Frobble cannot be overridden in a derived class.
Base<B> would be absurd because you cannot override a method that
doesn't exist in the base class.
Base<C> doesn't work because there is no Fiddle method to call.
Base<D> would not work because you cannot call an abstract method.
Only Base<E> would work.
How would the compiler ever know how to correctly compile Base<T> and analyse code that depends on it?
The point is that you cannot derive from a class that is not known at compile-time. T is a parameter, i.e. a variable, a placeholder. So class Base<T> : T is basically like saying, "Base<T> inherits from some (unknown) class". Class inheritance is a type relationship that requires both involved types to be known at compile-time. (Actually, that's not a super-precise statement because you can inherit from a generic type such as class SpecialList<T> : List<T>. But at the very least, the derived class has to know what members (methods, properties, etc.) are available in the base class.)
Is this what you want?
sealed public class Final : Base<int>{
}
public class Base<T> {
}
You could only do this if Final would be a generic class as well, like so:
public sealed class Final<T> : Base<T>
Then you can put a type restraint on T as either a class, to allow only reference types as T, or an instance of Base<T>, to allow only types that derive from Base<T>:
public class Base<T> where T : Base<T>
I don't know the context of this question, but I ran into same question with a project where I had to make it possible to extend the base class which is already derived by many others. Like:
abstract class Base {}
class FinalA : Base {}
class FinalB : Base {}
// Now create extended base class and expect final classes to be extended as well:
class BetterBase : Base {}
The solution was to create common ancestor and connect through properties:
abstract class Foundation {}
abstract class Base : Foundation
{
Foundation Final { get; }
}
class FinalA : Foundation {}
class FinalB : Foundation {}
class FinalC : Foundation
{
Foundation Base { get; }
}
// Here's the desired extension:
class BetterBase : Base {}
Now BetterBase has connection to final class and if needed, the final classes could have connection with (Better)Base also, as shown in FinalC class.
In an MVC project I have the following classes:
public abstract class Browse<T> where T : Browse<T>
public abstract class SqlBrowse<T> : Browse<T> where T : Browse<T>
public class SqlBrowseBoys : SqlBrowse<SqlBrowseBoys>
public class SqlBrowseGirls : SqlBrowse<SqlBrowseGirls>
and the following view model
public class BrowseViewModel
{
public [INTERFACE] People { get; set; }
}
but I need an interface/class in the position labelled [INTERFACE] that can take both SqlBrowseBoys and SqlBrowseGirls so I can use BrowseViewModel in multiple places.
I'd love it if someone could show me how as my brain is now tied in knots. I suspect this will require some change(s) to the classes and that's fine but I currently have no clue what that will be.
Many, many thanks.
Have SqlBrowse<T> implement a non-generic SqlBrowse interface (or abstract class), and then write
public SqlBrowse People { get; set; }
It's hard to tell what changes that will entail to your classes because we don't have their definitions.
I have a code template which builds files in a project's folder, and uses the properties defined in the partial classes to determine which properties still need to be implemented. As an example:
public partial class Thingy : IThingy
{
public Foo Bar { get; set; }
}
public interface IThingy
{
Foo Bar { get; set; }
Baz Biz { get; set; }
}
and the template is supposed to generate:
public partial class Thingy
{
Baz Biz { get; set; }
}
I can guarantee that the template will generate the remaining info to satisfy the expectations of the interface and thus would even be able to generate the class, except the CSharpCodeProvider balks at the notion of only getting half of the interface implemented in the non-generated partial class. Is there a way to tell the provider to ignore that an interface is being implemented at all?
EDIT: I've given this a little more thought, and figured a workaround in the form of actually reading the source first into a string, removing the interface references, and throwing the string of code to CompileAssemblyFromSource instead of CompileAssemblyFromFile, but that feels super kludgy and will more than likely introduce bugs. Thoughts?
You need to modify the source to remove interface implementation declaration, I think.
I am trying to register a type by convention, I've simplified my case in this example:
public abstract class BaseEntity{}
public class EntityA : BaseEntity{}
public class EntityB : BaseEntity{}
public abstract class BaseClass
{
//...
}
public abstract class GenericBaseClass<T> : BaseClass where T : BaseEntity
{
//..
}
public class ConcreteA : GenericBaseClass<EntityA>
{
//...
}
public class ConcreteB : GenericBaseClass<EntityB>
{
//...
}
I'm trying to find the way to register GenericBaseClass to return ConcreteA when requesting for GenericBaseClass<EntityA>. When trying to resolve this, I get an exception saying something like:
Activation error occured while trying to get instance of type
GenericBaseClass`1, key ""
If I change the definition of GenericBaseClass<T> from an abstract class to an interface, this registration code works:
container.Register(AllTypes.FromAssemblyContaining<BaseClass>()
.BasedOn(typeof(GenericBaseClass<>))
.WithService.FirstInterface());
However, I need to use an abstract class because I need to write code inside of it.
I can register manually every ConcreteX class, but it wouldn't be very helpful.
I've tried with this:
container.Register(AllTypes.FromAssemblyContaining<BaseClass>()
.BasedOn(typeof(GenericBaseClass<>))
.WithService.Base());
Debugging, I can see the type is not added to the container.
I am using Castle Windsor 2.6.
Thanks.
This works:
container.Register(AllTypes.FromAssemblyContaining<ConcreteA>()
.BasedOn(typeof (GenericBaseClass<>))
.WithService.Base());
If you see types not being added to the container make sure you're scanning the right assembly (the one which contains implementation types, not the service types).
If I have a class namespaceX.classA which uses namespaceX.classB is it possible to customise/overide/extend classB without breaking ClassA by using the same namespace (?) and class name? If so please could you explain how I go about doing this?
Example extend by adding methods to ColumnHeaderCollection without breaking ListView
Maybe. It depends on what you want to do and if you can modify class B.
Have a look at Extension Methods and Partial Classes.
Extension Methods let you create static methods in another static class (e.g. ClassBExtensions) that let you call them as if they were on ClassB. However you will not have access to any private or protected members in the extended class.
Partial Classes lets you add members directly to the class, but you need to be able to modify the source for ClassB since it needs to be declared partial in both places. Partial is really just a way to split a class definition into multiple files.
It sounds like you want an extension method.
public static class ColumnHeaderCollectionExtensions
{
public static void NewMethod(this ColumnHeaderCollection collection)
{
//do stuff here
}
}
You can then call it like:
myListView.Columns.NewMethod();
If the classes were in two separate namespace this would be possible. You cannot have two types of the same name within a namespace.
namespace Foo
{
class One : Bar.One
{
}
}
namespace Bar
{
class One
{
}
}
One purpose of namespaces is to address naming conflicts of same-name types.
Not directly. You will get a duplicate definition, the only time two classes with the same name in the same namespace that are both visible is allowed is if they vary by the number of generic type arguments they accept.
That said, you can add functionality if the original class is marked as partial.
// file 1
namespace A
{
public partial class B
{
public void AnOriginalMehtod() { ... }
}
}
// file 2
namespace A
{
public partial class B
{
public void AnotherMethod() { ... }
}
}
And you can also add extension methods to an existing class to give it more functionality.
// file 1
namespace A
{
public class B
{
public void SomeMethod()
{ ... }
}
}
// file 2
namespace A
{
public static class BExtensions
{
public static void SomeNewMethod(this B source)
{
// perform action on B
}
}
}
Partial classes let you flexibility by allowing you to divide a class into multiple files, but for this, to work the original class must be marked partial.
Extension methods are useful for adding functionality to existing classes or interfaces, but you must work with that interface or class through its public interface, you won't have access to private members.
Not quite sure what you want to do, but take a look "partial class".
like
// this bit of the class in a file
public partial class Employee
{
public void DoWork()
{
}
}
//this bit in another file
public partial class Employee
{
public void GoToLunch()
{
}
}