Is it possible to create a class during run-time and use it?
I am NOT referring to compiling code at run-time, generating a new assembly, loading it, executing it, etc. Reflection is a one-way street in that it can give you run-time info about your currently loaded assembly or one that you load from file or memory.
My question is more about injection I guess. Can you create a class at run-time within your own app domain and make it do anything useful?
Is it possible to create a class during run-time and use it?
Yes, you could use Reflection.Emit. You may also checkout Castle.DynamicProxy which simplifies the process of manually generating the IL.
Refer "Example 18-11: Dynamic invocation with reflection emit" section in following link:
How to create direct IL without .cs
namespace Programming_CSharp
{
using System;
using System.Diagnostics;
using System.IO;
using System.Reflection;
using System.Reflection.Emit;
using System.Threading;
// used to benchmark the looping approach
public class MyMath
{
// sum numbers with a loop
public int DoSumLooping(int initialVal)
{
int result = 0;
for(int i = 1;i <=initialVal;i++)
{
result += i;
}
return result;
}
}
// declare the interface
public interface IComputer
{
int ComputeSum( );
}
public class ReflectionTest
{
// the private method which emits the assembly
// using op codes
private Assembly EmitAssembly(int theValue)
{
// Create an assembly name
AssemblyName assemblyName =
new AssemblyName( );
assemblyName.Name = "DoSumAssembly";
// Create a new assembly with one module
AssemblyBuilder newAssembly =
Thread.GetDomain( ).DefineDynamicAssembly(
assemblyName, AssemblyBuilderAccess.Run);
ModuleBuilder newModule =
newAssembly.DefineDynamicModule("Sum");
// Define a public class named "BruteForceSums "
// in the assembly.
TypeBuilder myType =
newModule.DefineType(
"BruteForceSums", TypeAttributes.Public);
// Mark the class as implementing IComputer.
myType.AddInterfaceImplementation(
typeof(IComputer));
// Define a method on the type to call. Pass an
// array that defines the types of the parameters,
// the type of the return type, the name of the
// method, and the method attributes.
Type[] paramTypes = new Type[0];
Type returnType = typeof(int);
MethodBuilder simpleMethod =
myType.DefineMethod(
"ComputeSum",
MethodAttributes.Public |
MethodAttributes.Virtual,
returnType,
paramTypes);
// Get an ILGenerator. This is used
// to emit the IL that you want.
ILGenerator generator =
simpleMethod.GetILGenerator( );
// Emit the IL that you'd get if you
// compiled the code example
// and then ran ILDasm on the output.
// Push zero onto the stack. For each 'i'
// less than 'theValue',
// push 'i' onto the stack as a constant
// add the two values at the top of the stack.
// The sum is left on the stack.
generator.Emit(OpCodes.Ldc_I4, 0);
for (int i = 1; i <= theValue;i++)
{
generator.Emit(OpCodes.Ldc_I4, i);
generator.Emit(OpCodes.Add);
}
// return the value
generator.Emit(OpCodes.Ret);
//Encapsulate information about the method and
//provide access to the method's metadata
MethodInfo computeSumInfo =
typeof(IComputer).GetMethod("ComputeSum");
// specify the method implementation.
// Pass in the MethodBuilder that was returned
// by calling DefineMethod and the methodInfo
// just created
myType.DefineMethodOverride(simpleMethod, computeSumInfo);
// Create the type.
myType.CreateType( );
return newAssembly;
}
// check if the interface is null
// if so, call Setup.
public double DoSum(int theValue)
{
if (theComputer == null)
{
GenerateCode(theValue);
}
// call the method through the interface
return (theComputer.ComputeSum( ));
}
// emit the assembly, create an instance
// and get the interface
public void GenerateCode(int theValue)
{
Assembly theAssembly = EmitAssembly(theValue);
theComputer = (IComputer)
theAssembly.CreateInstance("BruteForceSums");
}
// private member data
IComputer theComputer = null;
}
public class TestDriver
{
public static void Main( )
{
const int val = 2000; // Note 2,000
// 1 million iterations!
const int iterations = 1000000;
double result = 0;
// run the benchmark
MyMath m = new MyMath( );
DateTime startTime = DateTime.Now;
for (int i = 0;i < iterations;i++)
result = m.DoSumLooping(val);
}
TimeSpan elapsed =
DateTime.Now - startTime;
Console.WriteLine(
"Sum of ({0}) = {1}",val, result);
Console.WriteLine(
"Looping. Elapsed milliseconds: " +
elapsed.TotalMilliseconds +
" for {0} iterations", iterations);
// run our reflection alternative
ReflectionTest t = new ReflectionTest( );
startTime = DateTime.Now;
for (int i = 0;i < iterations;i++)
{
result = t.DoSum(val);
}
elapsed = DateTime.Now - startTime;
Console.WriteLine(
"Sum of ({0}) = {1}",val, result);
Console.WriteLine(
"Brute Force. Elapsed milliseconds: " +
elapsed.TotalMilliseconds +
" for {0} iterations", iterations);
}
}
}