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.

Answer 1

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);