Getting all types in a namespace via reflection

Following code prints names of classes in specified namespace defined in current assembly.
As other guys pointed out, a namespace can be scattered between different modules, so you need to get a list of assemblies first.

string nspace = "...";

var q = from t in Assembly.GetExecutingAssembly().GetTypes()
        where t.IsClass && t.Namespace == nspace
        select t;
q.ToList().ForEach(t => Console.WriteLine(t.Name));

As FlySwat says, you can have the same namespace spanning in multiple assemblies (for eg System.Collections.Generic). You will have to load all those assemblies if they are not already loaded. So for a complete answer:

AppDomain.CurrentDomain.GetAssemblies()
                       .SelectMany(t => t.GetTypes())
                       .Where(t => t.IsClass && t.Namespace == @namespace)

This should work unless you want classes of other domains. To get a list of all domains, follow this link.

using System.Reflection;
using System.Collections.Generic;
//...

static List<string> GetClasses(string nameSpace)
{
    Assembly asm = Assembly.GetExecutingAssembly();

    List<string> namespacelist = new List<string>();
    List<string> classlist = new List<string>();

    foreach (Type type in asm.GetTypes())
    {
        if (type.Namespace == nameSpace)
            namespacelist.Add(type.Name);
    }

    foreach (string classname in namespacelist)
        classlist.Add(classname);

    return classlist;
}

NB: The above code illustrates what's going on. Were you to implement it, a simplified version can be used:

using System.Linq;
using System.Reflection;
using System.Collections.Generic;
//...

static IEnumerable<string> GetClasses(string nameSpace)
{
    Assembly asm = Assembly.GetExecutingAssembly();
    return asm.GetTypes()
        .Where(type => type.Namespace == nameSpace)
        .Select(type => type.Name);
}

For a specific Assembly, NameSpace and ClassName:

var assemblyName = "Some.Assembly.Name"
var nameSpace = "Some.Namespace.Name";
var className = "ClassNameFilter";

var asm = Assembly.Load(assemblyName);
var classes = asm.GetTypes().Where(p =>
     p.Namespace == nameSpace &&
     p.Name.Contains(className) 
).ToList();

Note: The project must reference the assembly

Here's a fix for LoaderException errors you're likely to find if one of the types sublasses a type in another assembly:

// Setup event handler to resolve assemblies
AppDomain.CurrentDomain.ReflectionOnlyAssemblyResolve += new ResolveEventHandler(CurrentDomain_ReflectionOnlyAssemblyResolve);

Assembly a = System.Reflection.Assembly.ReflectionOnlyLoadFrom(filename);
a.GetTypes();
// process types here

// method later in the class:
static Assembly CurrentDomain_ReflectionOnlyAssemblyResolve(object sender, ResolveEventArgs args)
{
    return System.Reflection.Assembly.ReflectionOnlyLoad(args.Name);
}

That should help with loading types defined in other assemblies.

Hope that helps!

You won't be able to get all types in a namespace, because a namespace can bridge multiple assemblies, but you can get all classes in an assembly and check to see if they belong to that namespace.

Assembly.GetTypes() works on the local assembly, or you can load an assembly first then call GetTypes() on it.

Just like @aku answer, but using extension methods:

string @namespace = "...";

var types = Assembly.GetExecutingAssembly().GetTypes()
    .Where(t => t.IsClass && t.Namespace == @namespace)
    .ToList();

types.ForEach(t => Console.WriteLine(t.Name));

Get all classes by part of Namespace name in just one row:

var allClasses = Assembly.GetExecutingAssembly().GetTypes().Where(a => a.IsClass && a.Namespace != null && a.Namespace.Contains(@"..your namespace...")).ToList();

Namespaces are actually rather passive in the design of the runtime and serve primarily as organizational tools. The Full Name of a type in .NET consists of the Namespace and Class/Enum/Etc. combined. If you only wish to go through a specific assembly, you would simply loop through the types returned by assembly.GetExportedTypes() checking the value of type.Namespace. If you were trying to go through all assemblies loaded in the current AppDomain it would involve using AppDomain.CurrentDomain.GetAssemblies()

//a simple combined code snippet 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;

namespace MustHaveAttributes
{
  class Program
  {
    static void Main ( string[] args )
    {
      Console.WriteLine ( " START " );

      // what is in the assembly
      Assembly a = Assembly.Load ( "MustHaveAttributes" );
      Type[] types = a.GetTypes ();
      foreach (Type t in types)
      {

        Console.WriteLine ( "Type is {0}", t );
      }
      Console.WriteLine (
         "{0} types found", types.Length );

      #region Linq
      //#region Action


      //string @namespace = "MustHaveAttributes";

      //var q = from t in Assembly.GetExecutingAssembly ().GetTypes ()
      //        where t.IsClass && t.Namespace == @namespace
      //        select t;
      //q.ToList ().ForEach ( t => Console.WriteLine ( t.Name ) );


      //#endregion Action  
      #endregion

      Console.ReadLine ();
      Console.WriteLine ( " HIT A KEY TO EXIT " );
      Console.WriteLine ( " END " );
    }
  } //eof Program


  class ClassOne
  {

  } //eof class 

  class ClassTwo
  {

  } //eof class


  [System.AttributeUsage ( System.AttributeTargets.Class |
    System.AttributeTargets.Struct, AllowMultiple = true )]
  public class AttributeClass : System.Attribute
  {

    public string MustHaveDescription { get; set; }
    public string MusHaveVersion { get; set; }


    public AttributeClass ( string mustHaveDescription, string mustHaveVersion )
    {
      MustHaveDescription = mustHaveDescription;
      MusHaveVersion = mustHaveVersion;
    }

  } //eof class 

} //eof namespace 

Quite simple

Type[] types = Assembly.Load(new AssemblyName("mynamespace.folder")).GetTypes();
foreach (var item in types)
{
}