Is it possible to have two parts (same namespace, same class name) to a partial class in separate DLLs?
From MSDN -Partial Classes and Methods:
All partial-type definitions meant to
be parts of the same type must be
defined in the same assembly and the
same module (.exe or .dll file).
Partial definitions cannot span
multiple modules.
No. Partial classes are a purely language feature. When an assembly is compiled, the files are combined to create the type. It isn't possible to spread the files out into different assemblies.
Depending on what you want to do, though, you might be able to use extension methods to accomplish what you need.
No it is not possible. When the assembly is compiled the class needs to be finished.
While other answers do provide the unpleasant "No" that anyone landing on this page didn't want to see, I was struck by another thought that hasn't been mentioned here yet. If partial classes were allowed across assemblies, one would get access to private members of existing types that were not written by him, thus allowing him to manipulate them in ways that were not intended by the original author, thus jeopardizing the functionality of all inheriting classes too.
Not only that, those classes in other assemblies (and their children) would need to be recompiled to make it work. Thus it is logically not possible to allow splitting a class over different assemblies.
Note: Read #Zar Shardan's comment below. That is another very important issue, even more important than private member access.
You can use extension methods when you want to add a method to a class in a different dll.
The one drawback of this method is that you cant add static methods.
The question is why would you want to make a partial class in another assembly? You can define abstract classes and interfaces across assemblies, maybe you need to look into that.
You probably just want to create a Wrapper class within you own library, around the class in the 3rd part library. Then add whatever functionality to the wrapper class.
Related
I have an architecture consisting of two DLLs and one executable. Both DLLs define a class with the same name and namespace, but potentially different implementations. What I would like to do is to create an object of each of those classes, and have both of them coexist at the same time.
But as we know a picture says more than a thousand words, so here you go:
The surprising thing is: it actually seems to work!
I have implemented a small prototype using lots of reflection to load the DLLs and instantiate the objects.
Now my question is: Why does this work?
Shouldn't there be a problem having both of the classes in the same AppDomain?
Is it safe to do it this way, or did I just get lucky?
A type is more than its class name and namespace. It also includes assembly information to qualify it. You can compare the AssemblyQualifiedName property of any System.Type and see that they are different.
I have two class libraries "MyLibrary.dll" and "MyLibraryEditor.dll" for a Unity runtime and editor extension. There are several class members inside "MyLibrary.dll" that are only intended for use by "MyLibraryEditor.dll".
My first thought was to use the internal keyword because I mistakenly thought that this constrained visibility to a namespace. Instead it is clear that this keyword limits visibility to the assembly.
What is the best way to constrain access to some class members to "MyLibrary.dll" and "MyLibraryEditor.dll" without hurting performance? Also, reflection is not an option.
I am happy to simply not document the functions, but unfortunately Intellisense (and MonoDevelop's equivalent) show these members.
If you want internals in one assembly to be visible from another assembly, you can use the InternalsVisibleTo attribute on the assembly containing the internals. See http://msdn.microsoft.com/en-us/library/system.runtime.compilerservices.internalsvisibletoattribute.aspx:
[assembly:InternalsVisibleTo("MyLibraryEditor")]
That answered, you might want to rethink your architectural design so that you don't need to use it, since it will open up all internals to the other assembly, not only the ones that you want.
You could make the members internal but use [InternalsVisibleTo] to give access to those members to the other assembly. They'd still be visible within the same assembly as well, of course... there's no way of getting round that.
I primarily use InternalsVisibleToAttribute for giving access to internal members to test classes, and would try to avoid doing this for non-test purposes - but sometimes it can be useful.
This is not possible using pure C# concepts. You are two seperate assemblies, that is as far seperate as you can get, and there is no relationship between the two as far as .Net is concerned.
you could do some things with signing or validation to make it so it would be difficult to use one assembly without the other, but not something you can do to prevent visibility of the classes/members.
Let's say I have a class (not a static class), A, that in some way uses plugins. I use MEF to manage those plugins, and add methods for my users to add parts catalogs. Example usage:
var myA = new A();
myA.LoadPlugins(new DirectoryCatalog("path/to/plugins"));
myA.DoStuffWithPlugins();
In the same namespace as A is class B. B also uses MEF to manage plugins, and has its own CompositionContainer. If a user wants to interact with B's plugins, she must use B's plugin management methods.
B is used just like A is, above.
My question is, is this bad? Should I care that there are two separate places to load plugins in my namespace? If it is bad, what are the alternatives?
My question is, is this bad? Should I care that there are two separate places to load plugins in my namespace? If it is bad, what are the alternatives?
Not necessarily. There is no reason you can't have two completely separate compositions within the same application.
That being said, there's also no real reason, in most cases, to have more than a single composition. MEF will compose both sets of data at once. In your case, you could compose your importers and your reports with the same composition container, which would have the advantage of allowing somebody who is extending your system to only create a single assembly which extends both portions of your application.
One potential minor red flag here is that these are two separate types within the same namespace, but each of which have their own plugin system. Typically, a framework with a full plugin system is going to be complex enough that I'd question whether they belong in the same namespace - though from going by type names of "A" and "B" it's impossible to know whether this is truly inappropriate.
I don't see any problem with that. I would recommend a base class for class A and class B to reuse methods.
class A : BaseCompositionClass {
// implementations
}
class B : BaseCompositionClass {
// implementations
}
You could use a single CatalogExportProvider and then query that provider for the matching imports and exports. You could then use a single CompositionFactory from which classA and classB request compositions.
With C++, I can have one class definition in a header file, and have a multiple implementation files by including the header file.
With C#, it seems that there is no such header file, as one class should contain both definition/implementation.
I wonder if the number of lines can be very big, because one can't separate the class into multiple files. Am I correct? I mean, in some cases, one can't change the class design to have smaller classes. In this case, is there a way to solve this problem?
You can separate a class into multiple files using the partial keyword
public partial class ClassNameHere
{
}
It is possible to split the definition of a class or a struct, or an interface over two or more source files using the Partial keyword modifier Link to msdn with the partial class
Partial classes only give you so much. There is still no way, that i know of, to split your class definition from implementation, such that each exists in a separate file. So if you like to develop based on a need-to-know paradigm then you are sort of stuck. Basically there are three levels a developer can work at...
1) Owns all the code and has access to, and maintains all of it.
2) Wishes to use some useful base class(s) which may form part of a framework, or may just be a useful class with some virtual methods, etc, and wishes to extend, or re-implement some virtual base class methods of interest. Now the developer should not need to go and look at the code in the base class(s) in order to understand things at a functional level. If you understand the job of a function, it's input and output parameters, there is no need to go and scratch inside source code. If you think there's a bug, or an optimization is needed, then refer to the developer from 1) who owns and maintains the base code. Of course there's nothing saying that 1) and 2) cannot be associated with the same developer, in which case we have no problem. In fact, this is more than often the case i suspect. Nevertheless, it is still good practice to keep things well separated according to the level at which you are working.
3) A developer needs to use an already packaged / sealed object / component dll, which exposes the relevant interfaces.
Within the context of c#, 1) and 3) have no problems. With 2) i believe there is no way to get round this (unless you change from exposing virtual base methods to exposing interface methods which can be reimplemented in a component owning the would-be base class). If i want to have a look at a class definition to browse over the methods, scaffolding functions, etc, i have to look at a whole lot of source code as well, which just gets in the way of what i am trying to focus on.
Of course if there is class definition documentation external to how we normally do it ( in headers and source files), then i must admit, that within the context of 2), there is not reason to ever look into a class definition file to gain functional knowledge.
So maybe clever Tom's came up with c#, decided to mix class definition with implementation in an attempt to encourage developers to have external documents for their class definitions, and interfaces, which in most IT companies is severely lacking.
Use a partial class as #sparks suggests, or, split into several classes. It's a good rule of thumb that, if you can't fit a class onto a couple of pages, it's complicated enough to need breaking apart.
I know it lets visual studio to separate WinForms UI code from the UI events, etc. But are there any practical uses for it?
The partial keyword is typically used in code generation utilities to allow developers to add additional functionality to the generated code without the fear of that code being erased if the code is generated again.
With C# 3 the partial keyword can be applied to methods to allow users of generated code to fill in blanks left by the generator. The Linq To Sql designer for example provides partial methods that allow you to add logic to the classes that the framework will call if implemented. The benefit here is that the C# compiler will completely remove unimplemented partial methods, so there is no performance hit at all for not implementing them.
Partial classes can also be used to organize very large classes into separate code files, although this sort of usage is usually a sign that your classes are too large and are taking on too many responsibilities.
The best use for the partial keyword that I can think of is nested classes. Without the partial keyword all nested classes must go in the same code file as the containing class.
One use I have found is for code that you may not want to exist in production code such as tracing or dev logging code. You could place this in the partial class and then when you do a production build you simply build without those partials included and the compiler will auto-magically strip out any calls to those partials that were excluded.
I'm using it for partitioning helper classes where some methods need lots of code. This is quite an easy way of retaining readability as each file only deals with a portion of the class's functionality.
In VB you can use it to separate "normal" code from code that needs late binding via "Option Strict Off".
In C# I only use it for unusually large classes.
The LINQ to SQL designer uses it extensively to split custom behaviors (partial methods) outside of the mapping class.
In short, its main purpose is for code generators.
Hope this helps.
I use partial classes and methods all the time with Linq2Sql. Otherwise I have never used it for anything besides UI/Code-behind classes.
One of the great things that I like about partial classes in linq2sql is that you can have the partial class inherit an interface and it will map the interface to the generated class. This is great if you have more than one Data provider and still want to use the same interfaces for all the Data access classes.
WPF uses partial classes extensively. The XAML generates a partial class that you can add to.
I use partial classes to reduce the merge pain with version control when I know that we would have several developers working on one class. For example, we often have our DAL class split into several partial class files. If you don't put them in different files, it's easy to get merge conflicts that take a while to fix when checked into version ctl.
When the develoment gets less chaotic as the class gets close to complete, we get rid of the partial files. We just use it to make VC/mulit-developer issues easier