Create a class dynamically with Reflection.Emit. I got stuck

Question

A read about creating types at runtime and i found it amazing. My goal is to create this class:

[DelimitedRecord(",")]
public class Person
{
    [FieldOrder(0)]
    private string firstName;

    [FieldOrder(1)]
    private string lastName;

    public string FirstName
    {
        get { return firstName; }
        set { firstName = value; }
    }

    public string LastName
    {
        get { return lastName; }
        set { lastName = value; }
    }
}

I did this:

//create the builder
AssemblyName assembly = new AssemblyName("FileHelpersTests");
AppDomain appDomain = System.Threading.Thread.GetDomain();
AssemblyBuilder assemblyBuilder = appDomain.DefineDynamicAssembly(assembly, AssemblyBuilderAccess.Run);
ModuleBuilder moduleBuilder = assemblyBuilder.DefineDynamicModule(assembly.Name);

//create the class
TypeBuilder typeBuilder = moduleBuilder.DefineType("Person", TypeAttributes.Public | TypeAttributes.AutoClass | TypeAttributes.AnsiClass |
                                                    TypeAttributes.BeforeFieldInit, typeof(System.Object));

//create the Delimiter attribute

//create the firstName field
FieldBuilder firstNameField = typeBuilder.DefineField("firstName", typeof(System.String), FieldAttributes.Private);

//create the firstName attribute [FieldOrder(0)]

//create the FirstName property
PropertyBuilder firstNameProperty = typeBuilder.DefineProperty("FirstName", PropertyAttributes.HasDefault, typeof(System.String), null);

//create the FirstName Getter
MethodBuilder firstNamePropertyGetter = typeBuilder.DefineMethod("get_FirstName", MethodAttributes.Public | MethodAttributes.SpecialName |
                                                                  MethodAttributes.HideBySig, typeof(System.String), Type.EmptyTypes);
ILGenerator firstNamePropertyGetterIL = firstNamePropertyGetter.GetILGenerator();
firstNamePropertyGetterIL.Emit(OpCodes.Ldarg_0);
firstNamePropertyGetterIL.Emit(OpCodes.Ldfld, firstNameField);
firstNamePropertyGetterIL.Emit(OpCodes.Ret);

//create the FirstName Setter
MethodBuilder firstNamePropertySetter = typeBuilder.DefineMethod("set_FirstName", MethodAttributes.Public | MethodAttributes.SpecialName |
                                                    MethodAttributes.HideBySig, null, new Type[] { typeof(System.String) });
ILGenerator firstNamePropertySetterIL = firstNamePropertySetter.GetILGenerator();
firstNamePropertySetterIL.Emit(OpCodes.Ldarg_0);
firstNamePropertySetterIL.Emit(OpCodes.Ldarg_1);
firstNamePropertySetterIL.Emit(OpCodes.Stfld, firstNameField);
firstNamePropertySetterIL.Emit(OpCodes.Ret);

//assign getter and setter
firstNameProperty.SetGetMethod(firstNamePropertyGetter);
firstNameProperty.SetSetMethod(firstNamePropertySetter);


//create the lastName field
FieldBuilder lastNameField = typeBuilder.DefineField("lastName", typeof(System.String), FieldAttributes.Private);

//create the lastName attribute [FieldOrder(1)]

//create the LastName property
PropertyBuilder lastNameProperty = typeBuilder.DefineProperty("LastName", PropertyAttributes.HasDefault, typeof(System.String), null);

//create the LastName Getter
MethodBuilder lastNamePropertyGetter = typeBuilder.DefineMethod("get_LastName", MethodAttributes.Public | MethodAttributes.SpecialName |
                                                                  MethodAttributes.HideBySig, typeof(System.String), Type.EmptyTypes);
ILGenerator lastNamePropertyGetterIL = lastNamePropertyGetter.GetILGenerator();
lastNamePropertyGetterIL.Emit(OpCodes.Ldarg_0);
lastNamePropertyGetterIL.Emit(OpCodes.Ldfld, lastNameField);
lastNamePropertyGetterIL.Emit(OpCodes.Ret);

//create the FirstName Setter
MethodBuilder lastNamePropertySetter = typeBuilder.DefineMethod("set_FirstName", MethodAttributes.Public | MethodAttributes.SpecialName |
                                                    MethodAttributes.HideBySig, null, new Type[] { typeof(System.String) });
ILGenerator lastNamePropertySetterIL = lastNamePropertySetter.GetILGenerator();
lastNamePropertySetterIL.Emit(OpCodes.Ldarg_0);
lastNamePropertySetterIL.Emit(OpCodes.Ldarg_1);
lastNamePropertySetterIL.Emit(OpCodes.Stfld, lastNameField);
lastNamePropertySetterIL.Emit(OpCodes.Ret);

//assign getter and setter
lastNameProperty.SetGetMethod(lastNamePropertyGetter);
lastNameProperty.SetSetMethod(lastNamePropertySetter);

I got stuck while creating those attributes:

The one at class level
The one at field level

This is what ILDASM shows when i click

The constructor

.class public auto ansi beforefieldinit FileHelpersTests.Person
    extends [mscorlib]System.Object
{
    .custom instance void [FileHelpers]FileHelpers.DelimitedRecordAttribute::.ctor(string) = ( 01 00 01 2C 00 00 )           // ...,..
} // end of class FileHelpersTests.Person

The firstName field

.field private string firstName
.custom instance void [FileHelpers]FileHelpers.FieldOrderAttribute::.ctor(int32) = ( 01 00 00 00 00 00 00 00 )

What does “LE” mean? Does it mean the class attribute works now? In any case, what have you tried and how did that fail? — svick
– svick, Commented Jan 23, 2013 at 13:38
Also, it's usually much easier to generate code by using C#-level libraries, like CodeDOM (if it can do what you need) or Roslyn. — svick
– svick, Commented Jan 23, 2013 at 13:40
What exactly do you need help with? Does your attribute not work? Is there an exception? — Gabe
– Gabe, Commented Jan 23, 2013 at 13:41
It now works, i just hurried and post it, anyway, it remains here as a full example of how to achieve it. — gigi
– gigi, Commented Jan 23, 2013 at 13:43

svick · Accepted Answer · 2013-01-23 14:10:50Z

4

I made it work:

//create the Delimiter attribute
Type[] attributeParams = new Type[] { typeof(string) };
ConstructorInfo classCtorInfo = typeof(DelimitedRecordAttribute).GetConstructor(attributeParams);
CustomAttributeBuilder attributeBuilder = new CustomAttributeBuilder(classCtorInfo, new object[] { ";" });
typeBuilder.SetCustomAttribute(attributeBuilder);

This would do the job for the field attributes:

//create the firstName attribute [FieldOrder(0)]
Type[] firstNameFieldOrderAttributeParams = new Type[] { typeof(int) };
ConstructorInfo firstNameFieldOrderAttrInfo = typeof(FieldOrderAttribute).GetConstructor(firstNameFieldOrderAttributeParams);
CustomAttributeBuilder firstNameFieldOrderAttributeBuilder = new CustomAttributeBuilder(firstNameFieldOrderAttrInfo, new object[] { 0 });
firstNameField.SetCustomAttribute(firstNameFieldOrderAttributeBuilder);

edited Jan 23, 2013 at 14:10

svick

247k54 gold badges405 silver badges535 bronze badges

answered Jan 23, 2013 at 13:45

gigi

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