I'm using a 3rd party library which requires a static method to be invoked before it is used - it sets the serial key to validate the license for the software. I'm needing to use this library in multiple projects and I want to shield those projects from needing to worry about this license. Ideally, I'd like to create a shared assembly which will handle the licensing and reference it by the projects which use the library - and isolate those projects from even knowing that any licensing is taking place.
One way to start thinking about accomplishing this is to perhaps use an assembly attribute. So, I make one which has a contructor to set the license:
[AttributeUsage(AttributeTargets.Assembly)]
public class LibraryLicenseAttribute : Attribute
{
public LibraryLicenseAttribute()
{
Lib.SetLicense("valid key");
}
}
and place it in a wrapper project:
LibraryWrapperProject
Properties
AssemblyInfo.cs
References
Lib.dll
LibraryLicenseAttribute.cs
And have it invoked by including it in AssemblyInfo.cs:
[LibraryLicense]
Now, I can reference this project in another project which uses the library:
LibraryUserProject
References
LibraryWrapperProject
LibraryUser.cs
... but when I go to use the library ...
class LibraryUser
{
public LibraryUser()
{
Lib.Use();
}
}
It reports that the license hasn't been set. I've found that I can include the attribute in the calling project's AssemblyInfo.cs and the attribute will get invoked. This is better than redistributing the licensing to all the downstream projects, but they still need that extra cruft to make it work.
Furthermore - some of the projects are dynamically loaded elseware. For instance:
Assembly.Load("LibraryUserProject.dll");
How can I invoke the licensing assembly attribute when dynamically loading the assembly it is contained in? Is there another .NET framework feature that might make this easier?
Without much analysing your solution to the problem, i suggest you to check out the AppDomain.CurrentDomain.AssemblyLoad and AppDomain.AssemblyResolve events for running your code when the assembly resolved or loadded.
Another and more elegant solution may be using a static type initializers (static constructor) or Module Initializers. Static type intitializers are called the first time the type is referenced and easy to implement. However, Module Initializers in C# is not a trivial task but you can achive your goal by implementing.
Related
I'm making a .Net application to manage and install mods. The application itself shouldn't be able to install mods for any particular game but should be able to call 3rd-party extensions to do so.
Let's say my mod manager expects an implementation of the given interface:
interface IGameManager {
// Deploy a modding configuration to the targeted game
void Deploy();
// Remove all managed mods from the targeted game
void Purge();
// ...
}
And someone else, working on a different code base, implement IGameManager to manage a specific game:
class MinecraftManager: IGameManager {
// ...
}
Then this person compiles it, publishes it and everyone could simply feed this extension to the main mod manager so it can manage their mods for the targeted game.
But how? Is there a way for my application to safely load and use such third-party implementations at run-time? And how to facilitate the making of third-party extension (e.g. giving an interface to build on but more elegantly and maintenance-friendly)?
Edit 1: Invalid syntax in MinecraftManager signature
You are essentially trying to design a plugin system. There are many implementations that you could reuse but the general idea is that:
You need your manager to be able to discover extensions. There are many ways to do that but the simplest and most used approach is to place extension assemblies under a well known directory in the file system. Then your manager can enumerate the assemblies in that folder by enumerating the files (or if you prefer that each extension has it own subfolder enumerate the subfolders)
Load the assembly. For that you will use one of the Assembly.Load.. methods. Since it is not possible to unload assemblies, you may want to first load the assembly for reflection only and once you decide that the assembly is valid you can load it in the ApplicationDomain in order to use it.
Use relfection to enumerate all classes of the assembly you just loaded and find the ones that implement the right interface (IGameManager). Altenatively you can require that extensions contains an "entry point" class of known name, then look for that class by name (using reflection).
Create an instance of the class(es) and use it (perhaps also keep it in a collection of loaded extensions)
Regarding the interface that extensions must implement: You should put the interface (and any other supporting interfaces) in a separate assembly. The assembly should contain only interfaces, no implementation. You can then publish the assembly. Once published the interface should never change.
If you need to add functionality you should create a new interface. This way old versions of the manager will work with newer versions of an extension (that is designed to implement the new functionality as well). Also your manager can determine which interfaces are implemented by an extension and act accordingly (thus maintaining compatibility). If the new functionality is mandatory, your manager should discard any extension that does not implement both interfaces.
I just found out dotNet 4 already have an extensibility framework (Documentations here), which is cleaner and safer than using Assembly.Load().
Here's the snippet I use to load my plugins from a given directory, if anyone encounter the same problem:
// Where T is the type you want to retrieve from the assemblies
private static IEnumerable<Lazy<T>> LoadExternalAssemblyFromPath<T>(string path, string pattern) {
CreateDirectoryIfDoesntExist(path);
AggregateCatalog catalog = new AggregateCatalog();
catalog.Catalogs.Add(new DirectoryCatalog(path, pattern));
CompositionContainer container = new CompositionContainer(catalog);
return container.GetExports<T>();
}
// Usage:
LoadExternalAssemblyFromPath("C:/path/to/plugins", "*.dll");
Regarding the implementation of such plugin, Kouvarakis' solution on the matter is correct.
In my .NET solution, I have two projects: one main project and a project for running tests against the main project. In my project, I have several methods that I'd like to keep "private", but would also like to run tests for. Is there an access method that could limit these functions to just inside of my solution?
You are looking for the InternalsVisibleTo attribute.
This attributes lets you specify other assemblies that should have access to types and methods that are internal to your assembly. So, in your main project AssemblyInfo.cs file (or any other source file), you can specify that your test project is a 'friend assembly' and should have access to the internals of your main project:
[assembly:InternalsVisibleTo("MainProject.Tests")]
On a side note, as pointed out by Alexei, if your MainProject is signed with a strong name key, any 'friend' assembly must also be signed. This is explained here
Although, as mentioned in another comment. Best practice is to test your assembly by using its public API.
You can use InternalsVisibleTo attribute to make internal types and methods visible to selected assemblies.
However, you should try to design your API so that it can be tested using only the public interface.
You should seriously think back about the architecture of your solution. This is a smell that often shows that your class does too much things at once.
A simple fix is to extract this responsibility (those private methods) to another class where they then become public and are testable out of the box...
No, there is no way to limit access to "just solution".
The reason is solution is simply group of projects. One project can be in any number of solutions. So even if you "limit" access to projects included in one solution you/someone else can create another solution that somehow will need to magically get access to methods.
Additionally built assembly does not include any information on what solution it was part of - so there is no information at run time to check access.
To you particular problem - InternalsVisibleTo (as shown in other answers) will give access to internal methods to projects you allow (requires strongly signed assemblies) or refactor your code to avoid need for testing private methods.
I am linking one of the external resource at runetime in my code using something like below:
System.Reflection.Assembly assembly = System.Reflection.Assembly.LoadFrom("MyNice.dll");
Type type = assembly.GetType("MyType");
Tool = Activator.CreateInstance(type) as Tool;
Now as you can see that at the end of the object creation, it has to cast the resulting object into the tool class because there are a lot of references to the methods and properties of Tool class in my code that if it is no there then the code will error out on compile time.
Now, this is a bad situation because I wanted to remove the Dll from my references and have it loaded dynamically at runtime but at the same to there are pieces of my code that referes to and are dependent to the Tool assembly. How can I make it independent? Do I have to use reflection all over my code or there is any easy alternative out there?
for example:
if (Tool.ApplicationIsOpen)
return StatusResult.Success;
is there in the same class which assumes that Tool class already exists and will break if I remove it from my references folder.
Any suggesitons?
I would suggest making shared DLL to reference from both projects that contains an interface in which Tool inherits.
In this shared project, make an interface such as ITool, that exposes the functionality you need for the consumer project.
Shared Project
public interface ITool
{
void Something();
}
Separate Project
public class Tool : ITool
{
public void Something()
{
// do something
}
}
Consumer Project
System.Reflection.Assembly assembly = System.Reflection.Assembly.LoadFrom("MyNice.dll");
Type type = assembly.GetTypes().FirstOrDefault(t => t.IsAssignableFrom(typeof(ITool)));
ITool tool = Activator.CreateInstance(type) as ITool;
Now you can delete the reference to the project containing Tool, but you still need the reference to the shared project that contains ITool. If you truly don't want any references, then explore the reflection route, but be warned it'll probably be messy.
This strategy is the basis for many plugin systems. I'd recommend you check out some Dependency Injection (DI for short) libraries that can do a lot of this heavy lifting for you.
Here is a list of DI libraries: http://www.hanselman.com/blog/ListOfNETDependencyInjectionContainersIOC.aspx
Personally I've been using Ninject lately.
Some relevant links:
Using Ninject in a plugin like architecture
Google something like "plugin framework DI C#"
This may be a long shot, but the flexibility of .NET never ceases to amaze me, so here goes.
I'm developing an MVC application that needs to search through a set of assemblies for class types that are derived from a common base class.
i.e. I have several assemblies that have activity types that are all derived from ActivityBase. These assemblies will be placed in a specific directory. They're kinda like plugins. Since they will need to be loaded dynamically at runtime, they will also need to be accompanied by some dependencies (unless I can figure out a convenient way to separate them, feel free to chime in on this as well.)
I have code that will iterate through all of the .DLL files in this directory, load the assembly, and iterate through all of the types in the assembly to find ones that are derived from ActivityBase.
This works fine. However, I would like to avoid loading and searching through the assemblies that do not have activities, because some of the dependencies have thousands of types and it becomes a performance problem.
So I guess my question is, other than a file naming convention, is there any way to "decorate" or mark an assembly with some type of data that would indicate that it is an activity assembly, that can be easily automated at build time and easily read at runtime?
Any other suggestions for handling this problem are also welcome.
You can implement your own assembly attribute:
[AttributeUsage(AttributeTargets.Assembly)]
public class ActivityAssemblyAttribute : Attribute
{
}
Then decorate necessary assembly with this attribute:
[assembly: ActivityAssemblyAttribute()]
And, when needed, just check whether the assembly under question is decorated with this attribute:
ActivityAssemblyAttribute attribute = null;
object[] attributes = assembly.GetCustomAttributes(typeof(ActivityAssemblyAttribute), false);
if (attributes.Length > 0)
{
attribute = attributes[0] as ActivityAssemblyAttribute;
}
I am working on a project and want to optionally use an assembly if available. This assembly is only available on WS 2008 R2, and my ideal product whould be a common binary for both computers with and without the assembly. However, I'm primarily developing on a Windows 7 machine, where I cannot install the assembly.
How can I organize my code so that I can (with minimum changes) build my code on a machine without the assembly and secondly, how do I ensure that I call the assembly functions only when it is present.
(NOTE : The only use of the optional assembly is to instantiate a class in the library and repeatedly call a (single) function of the class, which returns a boolean. The assembly is fsrmlib, which exposes advanced file system management operations on WS08R2.)
I'm currently thinking of writing a wrapper class, which will always return true if the assembly is not present. Is this the right way to go about doing this?
My approach would be to dynamically load the assembly, instead of hard-coding a reference. Your code could then decide whether to use the assembly (if it loaded) or return some other value. If you use the assembly, you'll need to use reflection to instantiate the class and use the method. That way your code will build and run on any platform, but it's behavior will change if it detects the presence of fsrmlib.
The System.Reflection.Assembly documentation has example code for doing this.
Hide the functionality behind an interface, say:
public interface IFileSystemManager
{
void Manage(IFoo foo);
}
Create two implementations:
An implementation that wraps the desired functionality from fsrmlib
A Null Object implementation that does nothing
Inject the IFileSystemManager into your consumers using Constructor Injection:
public class Consumer
{
private readonly IFileSystemManager fileSystemManager;
public Consumer(IFileSystemManager fileSystemManager)
{
if (fileSystemManager == null)
{
throw new ArgumentNullException("fileSystemManager");
}
this.fileSystemManager = fileSystemManager;
}
// Use the file system manager...
public void Bar()
{
this.fileSystemManager.Manage(someFoo);
}
}
Make the selection of IFileSystemManager a configuration option by delegating the mapping from IFileSystemManager to concrete class to the config file so that you can change the implementation without recompiling the application.
Configure applications running on WS 2008 R2 to use the implementation that wraps fsrmlib, and configure all other applications to use the Null Object implementation.
I would recommend that you use a DI Container for the configuration part instead of rolling this functionality yourself.
Alternatively you could also consider treating the IFileSystemManager as an add-in and use MEF to wire it up for you.