Question

In an assembly loaded into the current AppDomain using Assembly.LoadFrom, I have the following code:

[TypeConverter(typeof(EnumConverter<Shapes>))] public enum Shapes {   Triangle,   Square,   Circle } 

The generic EnumConverter<T> is defined in the assembly returned by calling Assembly.GetEntryAssembly(). When I read the TypeConverter attribute at runtime, I get the full name of the type which looks something like:

MyAssembly.EnumConverter`1[[MyDynamicAssembly.Shapes, MyDynamicAssembly, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]] 

However, when I call Type.GetType() on the string, it returns null. I expected to be able to get an instance of System.Type. Also note that MyDynamicAssembly was not generated by Reflection.Emit (pointed out in the MSDN article here).

This code was generated on Visual Studio 2005 using .NET Framework 2.0.

Has anyone found a workaround for this bug/limitation? Has it been fixed in 3.5?

Answer 1

After following a lead from an MSDN forum posting, I was able to put together a general solution for loading arbitrary generic types from assemblies loaded at runtime. I hope this helps some people (and maybe Microsoft will put something equivalent into .NET 4.0?)

public static class TypeHelpers {     /// <summary>     /// Gets the System.Type with the specified name, performing a case-sensitive search.     /// </summary>     /// <param name='typeName'>The assembly-qualified name of the type to get. See System.Type.AssemblyQualifiedName.</param>     /// <param name='throwOnError'>Whether or not to throw an exception or return null if the type was not found.</param>     /// <param name='ignoreCase'>Whether or not to perform a case-insensitive search.</param>     /// <returns>The System.Type with the specified name.</returns>     /// <remarks>     /// This method can load types from dynamically loaded assemblies as long as the referenced assembly      /// has already been loaded into the current AppDomain.     /// </remarks>     public static Type GetType(string typeName, bool throwOnError, bool ignoreCase)     {         if(string.IsNullOrEmpty(typeName))             throw new ArgumentNullException('typeName');          // handle the trivial case         Type type;         if((type = Type.GetType(typeName, false, ignoreCase)) != null)             return type;          // otherwise, perform the recursive search         try         {             return GetTypeFromRecursive(typeName, ignoreCase);         }         catch(Exception e)         {             if(throwOnError)                 throw;         }          return null;     }      #region Private Static Helper Methods      private static Type GetTypeFromRecursive(string typeName, bool ignoreCase)     {         int startIndex = typeName.IndexOf('[');         int endIndex = typeName.LastIndexOf(']');          if(startIndex == -1)         {             // try to load the non-generic type (e.g. System.Int32)             return TypeHelpers.GetNonGenericType(typeName, ignoreCase);         }         else         {             // determine the cardinality of the generic type             int cardinalityIndex = typeName.IndexOf('`', 0, startIndex);             string cardinalityString = typeName.Substring(cardinalityIndex + 1, startIndex - cardinalityIndex - 1);             int cardinality = int.Parse(cardinalityString);              // get the FullName of the non-generic type (e.g. System.Collections.Generic.List`1)             string fullName = typeName.Substring(0, startIndex);             if(typeName.Length - endIndex - 1 > 0)                 fullName += typeName.Substring(endIndex + 1, typeName.Length - endIndex - 1);              // parse the child type arguments for this generic type (recursive)             List<Type> list = new List<Type>();             string typeArguments = typeName.Substring(startIndex + 1, endIndex - startIndex - 1);             foreach(string item in EachAssemblyQualifiedName(typeArguments, cardinality))             {                 Type typeArgument = GetTypeFromRecursive(item, ignoreCase);                 list.Add(typeArgument);             }              // construct the generic type definition             return TypeHelpers.GetNonGenericType(fullName, ignoreCase).MakeGenericType(list.ToArray());         }     }      private static IEnumerable<string> EachAssemblyQualifiedName(string s, int count)     {         Debug.Assert(count != 0);         Debug.Assert(string.IsNullOrEmpty(s) == false);         Debug.Assert(s.Length > 2);          // e.g. '[System.String, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]'         // e.g. '[System.String, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.DateTime, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]'         // e.g. '[System.Collections.Generic.KeyValuePair`2[[System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.DateTime, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]], mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]'          int startIndex = 0;         int bracketCount = 0;          while(count > 0)         {             bracketCount = 0;              for(int i = startIndex; i < s.Length; i++)             {                 switch(s[i])                 {                     case '[':                         bracketCount++;                         continue;                      case ']':                         if(--bracketCount == 0)                         {                             string item = s.Substring(startIndex + 1, i - startIndex - 1);                             yield return item;                             startIndex = i + 2;                         }                         break;                      default:                         continue;                 }             }              if(bracketCount != 0)             {                 const string SR_Malformed = 'The brackets are unbalanced in the string, '{0}'.';                 throw new FormatException(string.Format(SR_Malformed, s));             }              count--;         }     }      private static Type GetNonGenericType(string typeName, bool ignoreCase)     {         // assume the type information is not a dynamically loaded assembly         Type type = Type.GetType(typeName, false, ignoreCase);         if(type != null)             return type;          // otherwise, search the assemblies in the current AppDomain for the type         int assemblyFullNameIndex = typeName.IndexOf(',');         if(assemblyFullNameIndex != -1)         {             string assemblyFullName = typeName.Substring(assemblyFullNameIndex + 2, typeName.Length - assemblyFullNameIndex - 2);             foreach(Assembly assembly in AppDomain.CurrentDomain.GetAssemblies())             {                 if(assembly.GetName().FullName == assemblyFullName)                 {                     string fullName = typeName.Substring(0, assemblyFullNameIndex);                     type = assembly.GetType(fullName, false, ignoreCase);                     if(type != null)                         return type;                 }             }         }          // no luck? blow up         const string SR_TypeNotFound = 'The type, '{0}', was not found.';         throw new ArgumentException(string.Format(SR_TypeNotFound, typeName), 'typeName');     }      #endregion } 

This code was tested both with the scenario above, and with the following MbUnit test:

[Test] public void GetType_DictionaryOfStringAndDictionaryOfInt32AndKeyValuePairOfStringAndListOfInt32() {     Dictionary<string, Dictionary<int, KeyValuePair<string, List<int>>>> obj =      new Dictionary<string, Dictionary<int, KeyValuePair<string, List<int>>>>();      string typeName = obj.GetType().FullName;     Type type = TypeHelpers.GetType(typeName, true, false);      Assert.IsTrue(type.Equals(obj.GetType())); } 

Note: You should comment out the trivial handler when trying to use this test, otherwise Type.GetType() will be called instead of the actual parsing code.