在使用Assembly.LoadFrom加载到当前AppDomain的程序集中,我具有以下代码：
[TypeConverter(typeof(EnumConverter<Shapes>))]
public enum Shapes
{
Triangle,
Square,
Circle
}
通用EnumConverter< T>在调用Assembly.GetEntryAssembly()返回的程序集中定义.当我在运行时读取TypeConverter属性时,将获得该类型的全名,如下所示：
MyAssembly.EnumConverter`1[[MyDynamicAssembly.Shapes, MyDynamicAssembly, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]
但是,当我在字符串上调用Type.GetType()时,它返回null.我希望能够获得System.Type的实例.还要注意,MyDynamicAssembly不是由Reflection.Emit生成的(在MSDN文章here中指出).
此代码是使用.NET Framework 2.0在Visual Studio 2005上生成的.
有没有人找到此错误/限制的解决方法？它已在3.5中修复吗？
解决方法:
在遵循了MSDN forum posting的指导之后,我能够提出一个通用解决方案,用于从运行时加载的程序集中加载任意泛型类型.我希望这对某些人有帮助(也许Microsoft会在.NET 4.0中投入等效的功能？)
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
}
上面的场景和下面的MbUnit测试都测试了此代码：
[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()));
}
注意：尝试使用此测试时,应注释掉琐碎的处理程序,否则将调用Type.GetType()而不是实际的解析代码.