In VS, I have referenced a DLL of a library.
I would like to use my own definition of a class that the library/api uses instead of the library's. I want to do this to add functionality to existing classes.
Class extensions do not suffice because I want to add new static methods to classes.
I have the source of the classes I want to reimplement.
Is there a way to redefine the class in my project and use it instead of the dll's class without importing the entire source of the library/dll. I'd rather not import the entire source, just the classes I want to modify.
In fact, the classes I want to modify are not classes but structs, and do not have the partial modifier.
Try extension methods:
namespace DLLNamespace
{
public struct TestStruct
{
public string Name { get; set; }
public void SetName(string name) { this.Name = name; }
}
}
namespace ProgramNamespace
{
public static class ExtensionMethods
{
public static void ReverseName(this DLLNamespace.TestStruct target)
{
target.Name = new string(target.Name.ToArray().Reverse().ToArray());
}
}
public class Program
{
static void Main(string[] args)
{
DLLNamespace.TestStruct ts;
ts.SetName("John");
ts.ReverseName();
Console.WriteLine(ts.Name);
}
}
}
Related
Recently, I had a need to process the private data contained in the base class using the methods of the child class. My base class could only contain domain-specific types (it only represents data). So first I decided to create a child-class in another project and implement the processing logic in it. But the problem is that once you create an instance of the base class, you can't cast it to the child type:
public class A
{
protected int member1;
public A(int value)
{
member1 = value;
}
}
public class B : A
{
public B (int value) : base(value)
{ }
public void DoSomething()
{
Console.Write(member1 * member1);
}
}
class Program
{
static void Main(string[] args)
{
A obj1 = new A(5);
B obj2 = (B)obj1; // InvalidCastException
obj2.DoSomething();
}
}
And I started thinking towards extension methods. However, you can't just access the protected fields of the class from them. In the end, I tried to combine the two approaches.
Here's my solution:
Make sure that you are allowed to add new methods to your base class and that your class is not sealed.
Add protected static method which returns the protected member you need.
Create an Extension class for your base class.
In extension class create a private nested class.
Inherit your nested class from your base class.
Create static method in nested class and implement the processing logic in (you can call static protected method from base class to get protected member from base class).
Create extension method in extension class and call static method of nested class in it.
The sample code is shown below:
public class A
{
protected int member1 = 0;
public A() {}
public A(int value)
{
member1 = value;
}
protected static int GetProtectedMember(A objA)
{
return objA.member1;
}
}
public static class AExtensions
{
public static void DoSomething(this A objA)
{
B.DoSomething(objA);
}
private class B : A
{
public static void DoSomething(A objA)
{
// objA.member1 // it's not allowed
int protectedFromA = A.GetProtectedMember(objA);
int sqr = protectedFromA * protectedFromA;
Console.WriteLine(sqr);
}
}
}
class Program
{
static void Main(string[] args)
{
A obj1 = new A(5);
obj1.DoSomething(); // 25
}
}
This way you can keep the classes that represent the data in a separate project and have multiple implementations of processing this data in different projects.
I'm trying to extend a generic type class, but I can't get VS to see the extension methods.
Of course there would be many ways around this and it sure isn't best practice in all situations, but I can't figure out why, of the two apparently identical cases below, the first one works and the other doesn't.
First, an example of a successful attempt to extend the List class (just to prove I can handle the basics):
namespace Sandbox.ExtensionsThatWork
{
public static class ListExtensions
{
public static List<TheType> ExtendedMethod<TheType>(this List<TheType> original)
{
return new List<TheType>(original);
}
}
public class ExtensionClient
{
public void UseExtensionMethods()
{
List<string> a = new List<string>();
List<string> b = a.ExtendedMethod();
}
}
}
However, the object I want to extend is something like this
namespace Sandbox.Factory
{
public class Factory<T>
{
public static Thing<T> Create()
{
return new Thing<T>();
}
}
public class Thing<T>{}
public static class FactoryExtensions
{
internal static Thing<FactoryType> CreateFake<FactoryType>(this Factory<FactoryType> original)
{
return new FakeThing<FactoryType>();
}
}
public class FakeThing<T> : Thing<T>{}
}
And in this case I can't for the life of me get the compiler to see the extension method.
namespace Sandbox.FactoryClients
{
public class FactoryClient
{
public void UseExtensionMethods()
{
Factory.Thing<int> aThing = Factory.Factory<int>.Create();
///THE COMPILER WON'T FIND THE CreateFake METHOD
Factory.Thing<int> aFakeThing = Factory.Factory<int>.CreateFake<int>();
}
}
}
What am I missing?
Thank you all for your time.
Your problem has nothing to do with generics.
You're calling the extension as if it were a static method of Factory.Factory<int>, which it cannot be.
C# does not support extension static methods (meaning extension methods that act like static methods of the type of the this parameter) on any type.
You need an instance to call the extension method on (like you do in your "working" example):
using Sandbox.Factory;
public void UseExtensionMethods()
{
Thing<int> aThing = Factory<int>.Create();
Thing<int> aFakeThing = new Factory<int>().CreateFake();
}
There must be something simple that I'm missing. I have two partial classes, in two different assemblies, and I'm not able to reference a private static method in one partial class from the other partial class.
For example, in the FirstHalf assembly, I have the following class:
namespace FirstHalf
{
public partial class TestPartialClass
{
private static void PrintFoo()
{
Console.WriteLine("Foo");
}
}
}
Then, in the SecondHalf assembly, I have the following class:
namespace FirstHalf
{
public partial class TestPartialClass
{
public static void Main(string[] args)
{
Console.WriteLine(PrintFoo());
}
}
}
However, when I try to invoke PrintFoo() from the SecondHalf assembly, I get the following error:
CS0103: The name 'PrintFoo' does not exist in the current context.
What's going on, here? I have a reference from SecondHalf to FirstHalf, so Visual Studio does know that there is a dependency between the two.
You can't split a partial class between two assemblies; they are actually being compiled as two different classes.
If you really want to accomplish something like this across assemblies, with sharing of 'private' members, you can get something similar by creating a base class and inheriting it:
namespace FirstHalf
{
public class Base
{
protected static void PrintFoo()
{
Console.WriteLine("Foo");
}
}
}
namespace SecondHalf
{
public class Derived : FirstHalf.Base
{
public static void Main(string[] args)
{
PrintFoo();
}
}
}
That said, there is probably a cleaner way to accomplish what you're trying to do using some form of composition; the details depend on your particular application.
I'd like to write an extension method that extends some member of my class. Specifically, I'd like to extend an enum. However, this is not working:
namespace mynamespace
{
public class myclass
{
public enum ErrorCodes
{
Error1, Error2, Error3
}
public static double GetDouble(this ErrorCodes ErrorCode)
{
return (double)((int)ErrorCode);
}
public void myfunc()
{
ErrorCodes mycode;
MessageBox.Show(mycode.GetDouble().ToString());
}
}
}
Specifically, it doesn't recognize GetDouble() as an extension. This is not just for enums either, I tried creating an extension method for doubles and had the same problem, too.
You can only write extension methods in top-level, static, non-generic classes, but they can extend nested classes. Here's a complete example, based on your code:
using System;
public static class Extensions
{
public static double GetDouble(this Outer.ErrorCode code)
{
return (double)(int)code;
}
}
public class Outer
{
public enum ErrorCode
{
Error1, Error2, Error3
}
}
public class Test
{
public static void Main()
{
Outer.ErrorCode code = Outer.ErrorCode.Error1;
Console.WriteLine(code.GetDouble());
}
}
The extension method must be defined in a static class.
See the manual.
edit
As Jon pointed out, the static class must be top-level, not nested.
I have a name space Company.Controls, which contains several controls. I also have a class called "Common" which contains enums/structures/static methods that I use throughout the controls.
Is there a way to make these "Common" peices belong to the Company.Controls namespace this way I don't have to keep typing "Common.Structure"? Essentially having he "Common" both a namespace and a class.
Just seems messy and confusing when reading the code.
example (all the other controls are in the Blah.Controls.Common namespace)
namespace Blah.Controls
{
public enum ControlTouchState
{
Down = 0x00,
Up = 0x01,
}
public Common()
{
//Stuff here
}
}
Thanks.
You can't get exactly what you want; in C# all methods have to be in a class.
Depending on what is in your Common class, you might be able to find something a slightly more satisfying by using extension methods:
namespace Blah.Controls
{
public class CommonControl { }
public static class Common
{
public static void Foo(this CommonControl cc) { }
}
public class Control1 : CommonControl
{
public void Bar()
{
this.Foo();
}
}
}
Another thing you might consider is using partial classes which would let you write simple wrappers elsewhere:
namespace Blop.Controls
{
public static class Common
{
public static void Foo() { }
}
public partial class Control1
{
public void Bar()
{
Foo();
}
}
public partial class Control1
{
public void Foo()
{
Common.Foo();
}
}
}
Obviously, introducing some inheritence could eliminate some of the duplication; I'm assuming you don't want to do that.
Is there some reason that the nested types in Common MUST be nested? Why not separate them out into their own namespace?
namespace Common
{
public struct Structure
{
// ...
}
public enum Enumeration
{
// ...
}
public class Common
{
// ...
}
}
You could then use the Common namespace as such:
namespace Blah.Controls
{
using Common;
class Control
{
Struct myStruct;
Enumeration myEnum;
Common myCommon; // references the class, not the namespace
}
}