可选的依赖关系处理（C＃） [英] Dealing with optional dependencies (C#)

问题描述

我们有哪些可选TFS中集成的应用，但是作为集成是可选的我明显的不希望将所有的机器所需要的TFS组件作为一项要求

We have an app which optionally integrates with TFS, however as the integration is optional I obviously don't want to have all machine need the TFS assemblies as a requirement.

我应该怎么办？

1. 它是确定由我来引用TFS库在我的主要组件和公正，确保当我使用TFS集成，我只引用TFS相关的对象。



2. 或者更安全的选择将是引用TFS库在某些单独的TFSWrapper组装：

1. Is it ok for me to reference the TFS libraries in my main assemblies and just make sure that I only reference TFS related objects when I'm using TFS integration.

2. Alternatively the safer option would be to reference the TFS libraries in some separate "TFSWrapper" assembly:

一。它是那么好，我直接引用该程序集（再次只要我小心我所说的）

a. Is it then ok for me to reference that assembly directly (again as long as I'm careful about what I call)

乙。我反而是暴露了一组接口，为我TFSWrapper组装来实现，然后在需要时使用反射实例化的对象。

b. Should I instead be exposing a set of interfaces for my TFSWrapper assembly to implement, and then instantiate those objects using reflection when required.

1，似乎有风险的我，在另一面2B似乎过度的顶部 - 我本质上可以构建一个插件系统

1 seems risky to me, on the flip side 2b seems over-the-top - I would essentially be building a plug-in system.

当然，必有是一个简单的方法。

Surely there must be a simpler way.

推荐答案

最安全的方式（即不使你的应用程序中的错误，最简单的方法）可能是因为。如下

The safest way (i.e. the easiest way to not make a mistake in your application) might be as follows.

请哪个抽象你TFS的使用，例如接口：

Make an interface which abstracts your use of TFS, for example:

interface ITfs
{
  bool checkout(string filename);
}

写它实现了使用TFS这个接口的类：

Write a class which implements this interface using TFS:

class Tfs : ITfs
{
  public bool checkout(string filename)
  {
    ... code here which uses the TFS assembly ...
  }
}

写

class NoTfs : ITfs
{
  public bool checkout(string filename)
  {
    //TFS not installed so checking out is impossible
    return false;
  }
}

有地方一个单：

Have a singleton somewhere:

static class TfsFactory
{
  public static ITfs instance;

  static TfsFactory()
  {
    ... code here to set the instance
    either to an instance of the Tfs class
    or to an instance of the NoTfs class ...
  }
}

的

现在，只有一个地方，需要小心（即TfsFactory构造函数）;其余的代码可以调用您的TfsFactory.instance的ITFS方法，不知道是否安装TFS的。

Now there's only one place which needs to be careful (i.e. the TfsFactory constructor); the rest of your code can invoke the ITfs methods of your TfsFactory.instance without knowing whether TFS is installed.

要回答下方最近的评论：

To answer recent comments below:

根据我的测试（我不知道这是否是'定义的行为）有异常时，（只要）你抛出一个叫方法，它依赖于丢失的组件。因此，在汇编封装代码 - 这-依赖 - 上的缺失组装至少在一个单独的方法（或一个单独的类）是很重要的。

According to my tests (I don't know whether this is 'defined behaviour') an exception is thrown when (as soon as) you call a method which depends on the missing assembly. Therefore it's important to encapsulate your code-which-depends-on-the-missing-assembly in at least a separate method (or a separate class) in your assembly.

例如，如果通话组件缺少以下将不会加载：

For example, the following won't load if the Talk assembly is missing:

using System;
using OptionalLibrary;

namespace TestReferences
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            if (args.Length > 0 && args[0] == "1") {
                Talk talk = new Talk();
                Console.WriteLine(talk.sayHello() + " " + talk.sayWorld() + "!");
            } else {
                Console.WriteLine("2 Hello World!");
            }
        }
    }
}

的

以下将加载：

The following will load:

using System;
using OptionalLibrary;

namespace TestReferences
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            if (args.Length > 0 && args[0] == "1") {
                foo();
            } else {
                Console.WriteLine("2 Hello World!");
            }
        }

        static void foo()
        {
            Talk talk = new Talk();
            Console.WriteLine(talk.sayHello() + " " + talk.sayWorld() + "!");
        }
    }
}

这是测试结果（使用Windows MSVC＃2010和.NET）：

These are the test results (using MSVC# 2010 and .NET on Windows):

C:\github\TestReferences\TestReferences\TestReferences\bin\Debug>TestReferences.exe
2 Hello World!

C:\github\TestReferences\TestReferences\TestReferences\bin\Debug>TestReferences.exe 1

Unhandled Exception: System.IO.FileNotFoundException: Could not load file or assembly 'OptionalLibrary, Version=1.0.0.0,
 Culture=neutral, PublicKeyToken=null' or one of its dependencies. The system cannot find the file specified.
   at TestReferences.MainClass.foo()
   at TestReferences.MainClass.Main(String[] args) in C:\github\TestReferences\TestReferences\TestReferences\Program.cs:
line 11

C:\github\TestReferences\TestReferences\TestReferences\bin\Debug>

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