I am trying to create a dynamic type based on an existing type that contains only public fields. The new dynamic type must also inherit from a different base type which only has a fully implemented method.
I create the TypeBuilder
specifying the base type then I add the public fields to it and finally I call CreateType()
. The resulting error message is:
"Could not load type 'InternalType' from assembly 'MyDynamicAssembly, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' because field 'first' was not given an explicit offset."
To me this implies that the CreateType
method is looking for the public field "first" in the base class which is a problem because it is not there. Why does it think the added field should be in the base class? Or, am I misunderstanding the exception?
Here is the code:
public class sourceClass
{
public Int32 first = 1;
public Int32 second = 2;
public Int32 third = 3;
}
public static class MyConvert
{
public static object ToDynamic(object sourceObject, out Type outType)
{
// get the public fields from the source object
FieldInfo[] sourceFields = sourceObject.GetType().GetFields();
// get a dynamic TypeBuilder and inherit from the base type
AssemblyName assemblyName
= new AssemblyName("MyDynamicAssembly");
AssemblyBuilder assemblyBuilder
= AppDomain.CurrentDomain.DefineDynamicAssembly(
assemblyName,
AssemblyBuilderAccess.Run);
ModuleBuilder moduleBuilder
= assemblyBuilder.DefineDynamicModule("MyDynamicModule");
TypeBuilder typeBuilder
= moduleBuilder.DefineType(
"InternalType",
TypeAttributes.Public
| TypeAttributes.Class
| TypeAttributes.AutoClass
| TypeAttributes.AnsiClass
| TypeAttributes.ExplicitLayout,
typeof(SomeOtherNamespace.MyBase));
// add public fields to match the source object
foreach (FieldInfo sourceField in sourceFields)
{
FieldBuilder fieldBuilder
= typeBuilder.DefineField(
sourceField.Name,
sourceField.FieldType,
FieldAttributes.Public);
}
// THIS IS WHERE THE EXCEPTION OCCURS
// create the dynamic class
Type dynamicType = typeBuilder.CreateType();
// create an instance of the class
object destObject = Activator.CreateInstance(dynamicType);
// copy the values of the public fields of the
// source object to the dynamic object
foreach (FieldInfo sourceField in sourceFields)
{
FieldInfo destField
= destObject.GetType().GetField(sourceField.Name);
destField.SetValue(
destObject,
sourceField.GetValue(sourceField));
}
// give the new class to the caller for casting purposes
outType = dynamicType;
// return the new object
return destObject;
}
Ok, I figured this out moments after posting. I was indeed misreading the error message. It, in fact, had nothing to do with the inherited base class.
When I created the type I specified the attribute "TypeAttributes.ExplicitLayout" which is required. Unfortunately, I didn't realize that I had to also add an offset to each field when I created them. The exception message was completely accurate. Sorry for the false alarm. The corrected code follows:
public class SourceClass
{
public Int32 first = 1;
public Int32 second = 2;
public Int32 third = 3;
}
public static class MyConvert
{
public static object ToDynamic(object sourceObject, out Type outType)
{
Int32 fieldOffset = 0;
// get the public fields from the source object
FieldInfo[] sourceFields = sourceObject.GetType().GetFields();
// get a dynamic TypeBuilder and inherit from the base type
AssemblyName assemblyName
= new AssemblyName("MyDynamicAssembly");
AssemblyBuilder assemblyBuilder
= AppDomain.CurrentDomain.DefineDynamicAssembly(
assemblyName,
AssemblyBuilderAccess.Run);
ModuleBuilder moduleBuilder
= assemblyBuilder.DefineDynamicModule("MyDynamicModule");
TypeBuilder typeBuilder
= moduleBuilder.DefineType(
"InternalType",
TypeAttributes.Public
| TypeAttributes.Class
| TypeAttributes.AutoClass
| TypeAttributes.AnsiClass
| TypeAttributes.ExplicitLayout,
typeof(SomeOtherNamespace.MyBase));
// add public fields to match the source object
foreach (FieldInfo sourceField in sourceFields)
{
FieldBuilder fieldBuilder
= typeBuilder.DefineField(
sourceField.Name,
sourceField.FieldType,
FieldAttributes.Public);
fieldBuilder.SetOffset(fieldOffset);
fieldOffset++;
}
// create the dynamic class
Type dynamicType = typeBuilder.CreateType();
// create an instance of the class
object destObject = Activator.CreateInstance(dynamicType);
// copy the values of the public fields of the
// source object to the dynamic object
foreach (FieldInfo sourceField in sourceFields)
{
FieldInfo destField
= destObject.GetType().GetField(sourceField.Name);
destField.SetValue(
destObject,
sourceField.GetValue(sourceObject));
}
// give the new class to the caller for casting purposes
outType = dynamicType;
// return the new object
return destObject;
}
EDIT: The above code won't work. The field index is in bytes so when you increment the offset you should do so by the size of the field like so:
fieldOffset += sizeof(Int32);