是否可以通过反射引用特定版本的装配？

Question

A colleague of mine wrote quite questionable piece of code some time ago, and eventually it got broken. Here's simplified sample:

Assembly assembly = typeof(SmtpClient).Assembly;
Type _mailWriterType = assembly.GetType("System.Net.Mail.MailWriter"); //getting a reference to internal class

//create an instance of System.Net.Mail.MailWriter storing it into _mailWriter variable
//It's internal, but for now it still works

MethodInfo _sendMethod = typeof(MailMessage).GetMethod("Send",BindingFlags.Instance | BindingFlags.NonPublic);

//calling non-public method resulting in app crash
_sendMethod.Invoke(
    message,
    BindingFlags.Instance | BindingFlags.NonPublic,
    null,
    new object[] { _mailWriter, true },
    null);

After some investigation it turned out that on my development machine there are indeed two parameters of MailMessage.Send method:

System.Net.Mime.BaseWriter writer
Boolean sendEnvelope

Hovewer, our QA engineers have installed VisualStudio 2012 recently, and got .NET 4.5 installed. So, when QA people try to run the application, they got System.Reflection.TargetParameterCountException . And, it looks like MailMessage.Send got third parameter in .NET 4.5:

System.Net.Mime.BaseWriter writer
Boolean sendEnvelope
Boolean allowUnicode

Of course we are to re-implement this piece of code to stop using non-public interfaces. Hovewer, we are on a tight schedule with a project, so we can't afford it right now.

So, here is a question: are there any ways to reference older (eg .NET 4.0) version of the assembly via reflection?

Answer 1

Instead of loading the Assembly with typeof(SmtpClient).Assembly you can load the assembly with Assembly.Load(AssemblyName) .

AssemblyName describes an assembly's unique identity in full. For example:

ExampleAssembly, Version=1.0.0.0, Culture=en, PublicKeyToken=a5d015c7d5a0b012

You can specify versioning information in your full assembly name.

Here is the MSDN documentation with more examples.

Answer 2

To get specific, do this

var systemNet35 = Assembly.Load(
    @"System.Net, Version=3.5.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL");

Type _mailWriterType = systemNet35.GetType("System.Net.Mail.MailWriter");

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Of course, this will only work with .Net 3.5 installed.