Recipe 12.1 Listing Imported Assemblies

Problem

You need to determine each assembly imported by a particular assembly. This information can show you if this assembly is using one or more of your assemblies or if your assembly is using another specific assembly.

Solution

Use the Assembly.GetReferencedAssemblies method to obtain the imported assemblies of an assembly:

using System;
using System.Reflection;
using System.Collections.Specialized;

public static void BuildDependentAssemblyList(string path, 
                                                StringCollection assemblies)
{
    // maintain a list of assemblies the original one needs
    if(assemblies == null)
            assemblies = new StringCollection( );

    // have we already seen this one?
    if(assemblies.Contains(path)==true)
        return;

    Assembly asm = null;
    // look for common path delimiters in the string 
    // to see if it is a name or a path
    if((path.IndexOf(@"\",0,path.Length)!=-1)||
        (path.IndexOf("/",0,path.Length)!=-1))
    {
        // load the assembly from a path
        asm = Assembly.LoadFrom(path);
    }
    else
    {
        // try as assembly name
        asm = Assembly.Load(path);
    }
    // add the assembly to the list
    if(asm != null)
    {
        assemblies.Add(path);
    }

    // get the referenced assemblies
    AssemblyName[] imports = asm.GetReferencedAssemblies( );
    // iterate
    foreach (AssemblyName asmName in imports)
    {
        // now recursively call this assembly to get the new modules 
        // it references
        BuildDependentAssemblyList(asmName.FullName,assemblies);
    }
}

This code fills a StringCollection containing the original assembly, all imported assemblies, and the dependent assemblies of the imported assemblies.

If you ran this method against the assembly C:\CSharpRecipes\bin\Debug\CSharpRecipes.exe, you'd get the following dependency tree:

  C:\CSharpRecipes\bin\Debug\CSharpRecipes.exe

  mscorlib, Version=1.0.5000.0, Culture=neutral, 
    PublicKeyToken=b77a5c561934e089

  System, Version=1.0.5000.0, Culture=neutral, PublicKeyToken=b77a5c561934e089

  System.Xml, Version=1.0.5000.0, Culture=neutral, 
    PublicKeyToken=b77a5c561934e089

  System.Runtime.Serialization.Formatters.Soap, Version=1.0.5000.0, 
    Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a

  REGEX_Test, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null

  FileIODenied, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null

  FileIOPermitted, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null

Discussion

Obtaining the imported types in an assembly is useful in determining what assemblies another assembly is using. This knowledge can greatly aid in learning to use a new assembly. This method can also help determine dependencies between assemblies for shipping purposes.

The GetReferencedAssemblies method of the System.Reflection.Assembly class obtains a list of all the imported assemblies. This method accepts no parameters and returns an array of AssemblyName objects instead of an array of Types. The AssemblyName type is made up of members that allow access to the information about an assembly, such as the name, version, culture information, public/private key pairs, and other data.

Note that this method does not account for assemblies loaded using the Assembly.Load* methods, as it is only inspecting for compile-time references.

See Also

See the "Assembly Class" topic in the MSDN documentation.