I created a assembly having a child class that derives from a parent defined in another assembly.
When I add reference to the child, Visula studio also requires reference to be added to the parent.
Why is it so and how can I prevent it without losing any functionality?
What you describe is partially possible. You can eliminate the need for them to explicitly reference the hidden assembly, but that assembly will still get pulled in at compiled time, and required at runtime.
Let's say you have these classes defined:
// in assembly 1:
public class A
{
public virtual void Foo() { }
}
// and in assembly 2:
// requires explicit reference to assembly 1 to use
public class B : A
{
public override void Foo() { }
public A Value { get; set; }
public void Foo(A value) { }
}
// has implicit reference to assembly 1, but end user can ignore
public class C
{
private A Value { get; set; }
internal void Foo(A value) { }
protected internal A Bar() { return new A(); }
}
// usable at runtime even if assembly 1 is missing, as long as you don't call Foo()
public class D
{
public void Foo() { A blah = new A(); }
public void Bar() { }
}
If the end user uses class B, they will require an explicit reference to assembly 1. Since A is part of B's public interface, in order to use B, you have to know about A. There are 3 different public references to A, and any of them will require knowing about A to use B.
However, class C makes references to A, but all references are private/internal/local. Since every reference to A is hidden from the outside, the end user doesn't have to explicitly know about assembly 1. It will still be required at runtime, but you don't have to add it as a reference, it's an indirect reference.
And if the end user uses class D, without ever using B or C, assembly 1 will only get loaded if you call D.Foo(), which has a local variable of type A. You can actually use D.Bar() freely even if assembly 1 is completely missing at runtime. Although if you call D.Foo() and assembly 1 is missing, you'll get an exception.
In C/C++, class definition is present in a .h header file. That gives you ability to reference information about a class (as needed e.g. when you want to inherit from that class) without the need to source file with implementation information. The downside is code duplication (implementation in .cpp file needs to repeat most of the information in .h file).
In .NET world the design is different: an assembly contains both the code for the class (CLR bytecode) as well as all the metadata (class name, information about its members etc.) needed to e.g. inherit from that class.
A consequence of that design is that in order to use a class defined in assembly A that inherits from a class in assembly B, .NET needs both A and B assemblies. Or more generically: if you use anything from a given assembly (a class, an enum, a struct), either directly or indirectly, you need to reference that assembly.
I'm not sure what you want to prevent. If you decide to split your code in two assemblies like you described, there's no way around the need to reference both of them.
There are, of course, different ways of structuring your code but not knowing what goal you're trying to achieve by splitting the code into 2 assemblies in the first place, it's impossible to make a useful suggestion.
Related
This question already has answers here:
How can I access an internal class from an external assembly?
(6 answers)
Closed 8 years ago.
I have a third party assembly and I would like to use its Internal class in my new C# project.
Is it possible?
Any example would really be appreciated
internal: The type or member can be accessed by any code in the same
assembly, but not from another assembly.
You can not use internal classes of other assemblies, the point of using internal access modifier is to make it available just inside the assembly the class defined.
if you have access to the assembly code and you can modify it you can make second assembly as a friend of your current assembly and mark the assembly with following attribute
[assembly: InternalsVisibleTo("name of assembly here")]
if not you can always use reflection but be aware that using reflection on a 3rd party assembly is dangerous because it is subject to change by the vendor. you can also decompile the whole assembly and use part of the code you want if it is possible.
Suppose you have this dll (mytest.dll say):
using System;
namespace MyTest
{
internal class MyClass
{
internal void MyMethod()
{
Console.WriteLine("Hello from MyTest.MyClass!");
}
}
}
and you want to create an instance of MyTest.MyClass and then call MyMethod() from another program using reflection. Here's how to do it:
using System;
using System.Reflection;
namespace MyProgram
{
class MyProgram
{
static void Main()
{
Assembly assembly = Assembly.LoadFrom("mytest.dll");
object mc = assembly.CreateInstance("MyTest.MyClass");
Type t = mc.GetType();
BindingFlags bf = BindingFlags.Instance | BindingFlags.NonPublic;
MethodInfo mi = t.GetMethod("MyMethod", bf);
mi.Invoke(mc, null);
Console.ReadKey();
}
}
}
If you're unable to modify and recompile the library, have a look at ImpromptuInterface.
https://www.nuget.org/packages/ImpromptuInterface/
Example:
namespace ImpromptuExample
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
// Get the desired type
Type typeObject = typeof(SampleLibrary.PublicClass).Assembly.GetType("SampleLibrary.SamplePrivateClass");
// todo: add error handling if typeObject is null
// Create an instance
object instance = Activator.CreateInstance(typeObject);
ITest wrappedInstance = ImpromptuInterface.Impromptu.ActLike<ITest>(instance);
MessageBox.Show(wrappedInstance.TestMethod(textBox1.Text));
}
public interface ITest
{
string TestMethod(string name);
}
}
}
namespace SampleLibrary
{
public class PublicClass
{
}
class SamplePrivateClass
{
public string TestMethod(string name)
{
return string.Concat("Hello ", name);
}
}
}
Internally, what ImpromptuInterface does is to create a dynamic assembly in memory and within that assembly, it creates a proxy class which implements the requested interface(s) and relays method calls and properties between the two. In the back end it still uses reflection but it is a slightly nicer encapsulation than doing it all through your own reflection.
Obviously there is an overhead involved with this but it is a viable last resort if you have no other option.
Useful features, include: the dynamic proxy class maps properties to fields, you can map interface methods to private, protected and internal methods in the original class. It doesn't work with static classes of methods, however.
You must create a friendly assembly, but you would need to recompile that third party assembly:
A friend assembly is an assembly that can access another assembly's
Friend (Visual Basic) or internal (C#) types and members. If you
identify an assembly as a friend assembly, you no longer have to mark
types and members as public in order for them to be accessed by other
assemblies.
You can use reflection though: How to access internal class using Reflection
Not recommendable anyway.
If it is an internal class, then the developer does not want you to use it. If you want to use a part of this code, just use Reflector and move it to a new class. It is not safe to use internal or private classes because the developer is not thinking of anyone other than themselves using it, and they could make changes in the future that break the functionality, they may not be thread safe, etc. So you should just respect their design.
You cannot do that. Have look here: Accessibility Levels (C# Reference)
My C# project has references to two third party DLLs. This is important because it means I don't have access to source code and can't modify or recompile these two DLLs.
Let's call them dll A and dll B. Here's what dll A looks like:
namespace ThirdParty.Foo
{
public class Bar
{
...snip...
}
public class Something
{
public Bar MyProperty { get; set; }
}
}
And here's what dll B looks like:
namespace ThirdParty.Foo
{
public class Bar
{
...snip...
}
public class SomethingElse
{
public Bar MyProperty { get; set; }
}
}
As you can see, they have the same namespace and they both define a class with the same name. My C# code needs a reference to both DLLs. I use the alias property on the reference to be able to distinguish between the two references and I also extern alias firstDll and extern alias secondDll at the top of my C# file. So far so good.
It seems obvious to me that the type of Something.MyProperty is firstDll.ThirdParty.Foo.Bar and the type of SomethingElse.MyProperty is secondDll.ThirdParty.Foo.Bar but for some reason, Visual Studio gets confused and resolves the type of both properties to the same Bar class in firstDll.
Is there a way for me to "force" VisualStudio to resolve the correct type?
EDIT:
the error I'm getting in Visual Studio is: Cannot implicitly convert type 'ThirdParty.Foo.Bar [d:\MySolution\References\Second.dll]' to 'ThirpParty.Foo.Bar [d:\MySolution\References\First.dll]'
Create a DLL that will serve as a wrapper for DLL A. Let's call the new DLL "C". Your project will then reference DLL B and C.
If the two types have the same name and namespace, then you are pretty much stuck. In C#, the name/identifier is quite important, "best fit" will only work in special situations.
However, you could write wrappers for the two different types, and make those wrappers have different names. By having two different (or even one) project just for the wrapper, you could have only one reference, thus effectively resolving the conflict "by force".
Something that works(for me it did referenced correctly) is the following,first(as you probably already did)click each dll in the references and assign an alias and place the proper extern alias.After to use the class Something and SomethingElse(and properly assign the Bar Property) create one class for each of those classes(Something and SomethingElse)and derive from them and shadow the MyProperty property:
public class TestFirst : first.ThirdParty.Foo.Something
{
//here you shadow and since you must provide the alias
//and the fully qualified name it will bet set to the
//right Bar class,same bellow in testsecond.
public first.ThirdParty.Foo.Bar MyProperty { get; set; }
}
public class TestSecond : second.ThirdParty.Foo.SomethingElse
{
public second.ThirdParty.Foo.Bar MyProperty { get; set; }
}
After its just business as usual:
TestSecond t = new TestSecond();
t.MyProperty = new second.ThirdParty.Foo.Bar();
I would load the dlls explicitly via Assembly.Load then do a createinstance on the types you need then invoke the methods via dynamic - that's because I am lazy.
The other (not lazy) way is to then use reflection to find the method and invoke it.
Since you have an extreme case here where the two assemblies not only have the same namespace, but also the same full assembly name (meaning the types have the same assembly-qualified name), you may want to consider more extreme measures to resolve it. If it's a fully managed DLL (no native code mixed in) and not strong named (or you're okay with removing the strong naming), you may be able to get away with a procedure like this:
Run ildasm and output to a .il file on disk.
Modify the .il file using a careful search and replace to change the root namespace for all types (be cautious for inner namespaces or type names that contain the same text as the root namespace.)
Run the modified file through ilasm to build a new .dll with the changes.
You can use the keyword var instead of specifying the type explicitly to avoid ambiguous references
var x = new ThirdParty.Foo.Something();
var y = new ThirdParty.Foo.SomethingElse();
var barX = x.MyProperty;
var barY = y.MyProperty;
I created the Class1.GetChild<T>() where T : DependencyObject extension method in lib1.dll assembly. After that, all assemblies that depends on lib1.dll failed to compile with error:
The type 'System.Windows.DependencyObject' is defined in an assemebly
that is not referenced. You must add a reference to assembly
'WindowsBase' etc...
Why dependent assemblies requires WindowsBase even if they don't use GetChild?
.
To reproduce (vs2010 .net4):
lib1.dll (references WindowsBase)
namespace lib1
{
public static class Class1
{
public static T GetChild<T>(this DependencyObject src) where T : DependencyObject
{
return default(T);
}
}
public static class Class2
{
public static int SomeExtMethod(this string src)
{
return 0;
}
}
}
lib2.dll (references lib1 but not WindowsBase)
using lib1;
class someClass
{
void someFct()
{
"foo".SomeExtMethod(); // error: The type 'System.Windows.DependencyObject'
// is defined in an assemebly that is not referenced.
// You must add a reference to assembly 'WindowsBase' etc..
}
}
.
Update:
I think there's definitly something when mixing generic methods and extension methods. I tried to demonstrate the issue in the following sample:
// lib0.dll
namespace lib0
{
public class Class0 { }
}
// lib1.dll
using lib0;
namespace lib1
{
public static class Class1
{
public static void methodA<T>() where T : Class0 { } // A
public static void methodB(Class0 e) { } // B
public static void methodC(this int src) { } // C
}
public static class Class2
{
public static void methodD(this String s) { }
}
}
// lib2.dll
using lib1;
class someClass
{
void someFct()
{
Class2.methodD(""); // always compile successfully
"".methodD(); // raise the 'must add reference to lib0' error depending on config. see details below.
}
}
A, //B, //C -> compile ok
A, B, //C -> compile ok
//A, B, C -> compile ok
A, //B, C -> raise error
A, B, C -> raise error
//A means methodA is commented. As Damien pointed out, type inference might play some role. Still curious to know the ins and outs.
Your situation has been answered by Microsoft here:
https://connect.microsoft.com/VisualStudio/feedback/details/668498/problem-with-extension-method-in-c-compiler
There are other use-cases as well independent of extension methods which produce this error wrongly.
Consider this:
Define a generic method in a type, say TP1, defined in library say LB1.
Type constrain the generic method on some type defined in some other library LB2.
Define another method in TP1.
Now in your library reference only LB1 and try to call the second method of type TP1
If you don't use TP1 but some other type defined in LB1, you do not get the error.
Also, even if one of the method of type TP1 expects a parameter of the type defined in LB2 (and you do not call this method) it does not produce this error
When one assembly depends on another assembly, the first assembly also depends on all the dependencies of the other--regardless of what is used. Assembly dependencies are effectively decoupled, another version of either assembly can be deployed after compilation, the compiler can't know that under circumstances like this one or more of the dependencies in the second assembly won't be used by the first assembly.
To solve the issue you can simply add a reference to WindowsBase.
Or, as prashanth points out, put the SomeExtMethod into a different assembly so code that uses that doesn't need to take a dependency on WindowsBase.
Update:
If you don't use anything from an assembly, you don't need any of its dependencies. But, as soon as you use one assembly, you need all the dependencies of that assembly as well. This is apparent in the way Visual Studio add references. If you add a reference to an assembly, it will copy all the dependent assemblies (not registered in the GAC) into your debug/release directories along with the assembly you added.
Update:
As to the compile error: that's the way it was written--there may be no other reason. Is it a good idea to get a compile error if you don't reference dependent assemblies? Maybe, you're likely to use something from a reference and that might use something directly from the references references--better a compile error than a deployment error.
Why not a compile error on every non-referenced secondary dependency? Again, it was written that way. Maybe an error here too would be good; but that would be a breaking change and would require really persuasive reasons.
I'm not sure this can be answered by anyone other than someone on the compiler team. I'm now thinking that it's to do with type inference - but whereas §7.6.5.1 Method Invocations talks about inference, §7.6.5.2 Extension method invocations is silent on the matter - despite the fact that inference obviously does take place when searching for applicable extension methods.
I think it's attempting some form of inference before it's performing the comparison on identifiers (which would immediately rule out the extension method since it's got the wrong name). Obviously, it can't perform any form of inference for this type if it's unable to understand the type constraints.
Hence, when you change your type constraint to just class, it now successfully passes over this method - it can infer a type parameter, but it now eliminates this extension method successfully.
When you reference another assembly, I assume the compiler needs to be able to parse any method signatures defined in that assembly, so it knows where to go to find that function if it sees a call to it.
If you replace your GetChild() function with
public static T GetChild<T>(this T src)
{
if (typeof(T) == typeof(DependencyObject)) return default(T);
else return default(T);
}
or something similar to that, it does not require you to include the reference to WindowsBase that you're running into. But if you add where T : DependencyObject to the signature, it does require it.
Effectively, you can use whatever assembly references you want in a project, so long as you don't expose them in any way. Once you expose them, then every other project which uses your library needs to be able to handle them, and thus requires those references themselves.
Maybe ILMerge would solve this problem. The idea is you create 2 dlls and merge them into one. That way you can have a single dll but reference it twice. Then way you can separate the GUI code from other code and only add the reference that you need to the particular project.
The answer is simple. It is because the method is decalre as public. This mean that it is visible to lib2.dll (in your case.) In other word you can call this method.
It also has a constrain that only classes inherited from DependencyObject can call this method. So that is the reason why you need to reference 'WindowsBase'.
I have the following code returning the error " 'object' does not contain a constructor that takes x arguments." on the line trying to call the base constructor.
Solution 1, project 1
namespace Project.Sub.A
{
internal class Foo
{
internal Foo(int a, long b) {}
}
}
Solution 1,project 2
namespace Project.Sub.B{
internal class Bar : Foo
{
internal Bar(int a, long b,long c) :base(a,b+c) {}
}
}
I have NO idea why this does not want to work. Could be my namespaces configured incorrectly?
internal access is per assembly, not namespace.
Because the constructor in the base class is declared internal, it is not accessible to the subclass in the other project. Try changing it to protected internal, or just protected.
update
Just noticed that the base class is also internal. You will need to make it public if you want it to be seen in the second project. Or, you can add [assembly:InternalsVisibleTo("Project2")] in AssemblyInfo.cs in Project1. (I wouldn't personally recommend this option, though.)
There are a number of confounding issues here.
First, your classes are defined as internal in two separate projects. internal means that a class is only visible within its own assembly and not to client code outside of the assembly. Foo should be public so that it can be used in other assemblies
If you make class Foo visible outside of the assembly then you will have to reference that assembly from the project that contains class Bar
And you will have to make sure that the namespaces are referenced properly as well
internal means visible to other classes in the current assembly
Because you're defining your second class in a second project, it can't see that base constructor.
Try making both the Foo Class & Constructor protected instead or internal.
If it's in a separate project as your question suggests, and your base class is marked internal, then it shouldn't be able to find the entire type, let alone the constructor.
Change Foo' accessor to public.
I'm a C# newbie, so please bear with me.
OK, so I have two classes in different assemblies that need to reference each other:
namespace AssemblyA
{
class A
{
private B MyB { get; set; }
}
}
namespace AssemblyB
{
class B
{
private A MyA { get; set; }
}
}
I understand that circular references aren't allowed, so I'm using an interface:
namespace AssemblyA
{
public interface IB
{
// whatever 'A' needs of 'B'
}
class A
{
private IB MyB { get; set; }
}
}
namespace AssemblyB
{
class B : AssemblyA.IB
{
private A MyA { get; set; }
}
}
This works, but it has the disadvantage that it exposes IB to the rest of the world. What I would like to do instead is to make IB internal. But then B cannot derive from it.
In C++, I'd make B a friend and be done. I understand that C# doesn't have friends (pun not intended, but noted), so I have to make do without. I've read that there is an attribute for that, but this will make the whole of assembly A accessible to the whole of assembly B, which I don't like. Is there a way to avoid that?
You've in fact been misinformed - C#/.NET does indeed have support for friend assemblies. You want to mark your two assemblies as Friend Assemblies, which MSDN defines as the following:
An internal type or internal member in an assembly can be accessed from another assembly.
So, simply place the following attribute anywhere in one of your code files in your project (I would choose AssemblyInfo.cs).
[assembly:InternalsVisibleTo("name_of_friend_assembly")]
It seems that the big issue here is letting assembly B see one specific member of assembly A.
This negates, according to the comments reiterating part of the original question, the feasibility of using the well-documented InternalsVisibleTo attribute.
Or does it?
Have you considered making a new assembly, C, with the IB interface marked internal and its own InternalsVisibleTo attributes out to A and B?
This at least exposes IB in a controlled fashion, without exposing all of A to B. I'm not a huge fan of the solution (I would personally just go ahead and use InternalsVisibleTo on A as has been suggested, then document the rest of my internals to keep others in line), but I understand where you're coming from -- and this at least solves the problem.
You could use InternalsVisibleToAttribute
http://msdn.microsoft.com/en-us/library/system.runtime.compilerservices.internalsvisibletoattribute.aspx