Problem creating type with Reflection

Question

I got a following base class:

public class ValidationItem 
{
    public ObservableCollection<object> GetFilteredValues( ObservableCollection<object> values)
    {
        return new ObservableCollection<object>(); // nothing here yet
    }

}

I create a type which inherits this base type and I create a getter which is going to return a base class GetFilteredValues method result.

This is how a new property should look like:

public ObservableCollection<object> Values
{
    get { return GetFilteredValues(_values); }
    set { _values = value; }
}

This is what I do:

Type pType = typeof(ObservableCollection<object>);

FieldBuilder fieldBuilder = tb.DefineField("_" + propertyName, pType, FieldAttributes.Private);

PropertyBuilder propertyBuilder = tb.DefineProperty( propertyName, PropertyAttributes.HasDefault, pType, null);

MethodBuilder getPropMthdBldr = tb.DefineMethod("get_" + propertyName,
                                MethodAttributes.Public |
                                MethodAttributes.SpecialName |
                                MethodAttributes.HideBySig,
                                pType, Type.EmptyTypes);
getPropMthdBldr.SetReturnType(typeof(ObservableCollection<>).MakeGenericType(typeof(object)));
ILGenerator getIL = getPropMthdBldr.GetILGenerator();

MethodInfo minfo = typeof(ValidationItem).GetMethod("GetFilteredValues", new[] { typeof(ObservableCollection<object>) }); // it's not null so everything is ok here

getIL.Emit(OpCodes.Ldarg_0);
getIL.Emit(OpCodes.Ldfld, fieldBuilder);
getIL.EmitCall(OpCodes.Callvirt, minfo, Type.EmptyTypes);
getIL.Emit(OpCodes.Ret);

propertyBuilder.SetGetMethod(getPropMthdBldr);

But each time I run an app and use this created type, I get an error "Common Language Runtime detected an invalid program". What am I doing wrong?

Thanks in advance.

Have you tried writing the DynamicAssembly to disk and running it through peverify? peverify normally gives good error messages. — Tim Robinson
– Tim Robinson, Commented Jul 26, 2010 at 12:40
Is your main goal to create an instance of this concrete type using reflection or actually create THE type during runtime? — Wallace Breza
– Wallace Breza, Commented Jul 26, 2010 at 12:48
2Tim: I cannot save assembly because I use Silverlight. 2Wallace: Yes I must create an instance — Maxmyd
– Maxmyd, Commented Jul 27, 2010 at 8:35

Quartermeister · Accepted Answer · 2010-07-26 12:54:27Z

4

When you call GetFilteredValues, the only thing on the stack is the ObservableCollection<object>. Since GetFilteredValues is an instance method, you also need to push this. Add a second Ldarg_0 before the existing one so that you push it on the stack before _values:

getIL.Emit(OpCodes.Ldarg_0);
getIL.Emit(OpCodes.Ldarg_0);
getIL.Emit(OpCodes.Ldfld, fieldBuilder);
getIL.EmitCall(OpCodes.Callvirt, minfo, Type.EmptyTypes);
getIL.Emit(OpCodes.Ret);

answered Jul 26, 2010 at 12:54

Quartermeister

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Comments

abatishchev · Accepted Answer · 2010-07-26 13:11:02Z

3

As per documentation to Ldfld, stack transition is the following

An object reference (or pointer) is pushed onto the stack.
The object reference (or pointer) is popped from the stack; the value of the specified field in the object is found.
The value stored in the field is pushed onto the stack.

So after executing

getIL.Emit(OpCodes.Ldarg_0);
getIL.Emit(OpCodes.Ldfld, fieldBuilder);

you will have only field reference on the evaluation stack (without 'this'). To fix, duplicate arg_0

getIL.Emit(OpCodes.Ldarg_0);
getIL.Emit(OpCodes.Dup);
getIL.Emit(OpCodes.Ldfld, fieldBuilder);
getIL.EmitCall(OpCodes.Callvirt, minfo, Type.EmptyTypes);
getIL.Emit(OpCodes.Ret);

This should help.

edited Jul 26, 2010 at 13:11

abatishchev

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answered Jul 26, 2010 at 13:08

desco

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