How to dynamically create a class?

Question

I have a class which looks like this:

public class Field {     public string FieldName;     public string FieldType; } 

And an object List<Field> with values:

{"EmployeeID","int"}, {"EmployeeName","String"}, {"Designation","String"} 

I want to create a class that looks like this:

Class DynamicClass {     int EmployeeID,     String EmployeeName,     String Designation } 

Is there any way to do this?

I want this to be generated at runtime. I don't want a physical CS file residing in my filesystem.

Answer 1

Yes, you can use System.Reflection.Emit namespace for this. It is not straight forward if you have no experience with it, but it is certainly possible.

Edit: This code might be flawed, but it will give you the general idea and hopefully off to a good start towards the goal.

using System; using System.Reflection; using System.Reflection.Emit;  namespace TypeBuilderNamespace {     public static class MyTypeBuilder     {         public static void CreateNewObject()         {             var myType = CompileResultType();             var myObject = Activator.CreateInstance(myType);         }         public static Type CompileResultType()         {             TypeBuilder tb = GetTypeBuilder();             ConstructorBuilder constructor = tb.DefineDefaultConstructor(MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.RTSpecialName);              // NOTE: assuming your list contains Field objects with fields FieldName(string) and FieldType(Type)             foreach (var field in yourListOfFields)                 CreateProperty(tb, field.FieldName, field.FieldType);              Type objectType = tb.CreateType();             return objectType;         }          private static TypeBuilder GetTypeBuilder()         {             var typeSignature = "MyDynamicType";             var an = new AssemblyName(typeSignature);             AssemblyBuilder assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(an, AssemblyBuilderAccess.Run);             ModuleBuilder moduleBuilder = assemblyBuilder.DefineDynamicModule("MainModule");             TypeBuilder tb = moduleBuilder.DefineType(typeSignature,                     TypeAttributes.Public |                     TypeAttributes.Class |                     TypeAttributes.AutoClass |                     TypeAttributes.AnsiClass |                     TypeAttributes.BeforeFieldInit |                     TypeAttributes.AutoLayout,                     null);             return tb;         }          private static void CreateProperty(TypeBuilder tb, string propertyName, Type propertyType)         {             FieldBuilder fieldBuilder = tb.DefineField("_" + propertyName, propertyType, FieldAttributes.Private);              PropertyBuilder propertyBuilder = tb.DefineProperty(propertyName, PropertyAttributes.HasDefault, propertyType, null);             MethodBuilder getPropMthdBldr = tb.DefineMethod("get_" + propertyName, MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig, propertyType, Type.EmptyTypes);             ILGenerator getIl = getPropMthdBldr.GetILGenerator();              getIl.Emit(OpCodes.Ldarg_0);             getIl.Emit(OpCodes.Ldfld, fieldBuilder);             getIl.Emit(OpCodes.Ret);              MethodBuilder setPropMthdBldr =                 tb.DefineMethod("set_" + propertyName,                   MethodAttributes.Public |                   MethodAttributes.SpecialName |                   MethodAttributes.HideBySig,                   null, new[] { propertyType });              ILGenerator setIl = setPropMthdBldr.GetILGenerator();             Label modifyProperty = setIl.DefineLabel();             Label exitSet = setIl.DefineLabel();              setIl.MarkLabel(modifyProperty);             setIl.Emit(OpCodes.Ldarg_0);             setIl.Emit(OpCodes.Ldarg_1);             setIl.Emit(OpCodes.Stfld, fieldBuilder);              setIl.Emit(OpCodes.Nop);             setIl.MarkLabel(exitSet);             setIl.Emit(OpCodes.Ret);              propertyBuilder.SetGetMethod(getPropMthdBldr);             propertyBuilder.SetSetMethod(setPropMthdBldr);         }     } } 

Answer 2

It will take some work, but is certainly not impossible.

What I have done is:

• Create a C# source in a string (no need to write out to a file),
• Run it through the Microsoft.CSharp.CSharpCodeProvider (CompileAssemblyFromSource)
• Find the generated Type
• And create an instance of that Type (Activator.CreateInstance)

This way you can deal with the C# code you already know, instead of having to emit MSIL.

But this works best if your class implements some interface (or is derived from some baseclass), else how is the calling code (read: compiler) to know about that class that will be generated at runtime?