Buu Nguyen's Blog

Presentation I gave at the Success in IT Career event organized by KMS Technology last Saturday.

Slides for the C# training I conducted for Microsoft’s customers in Ho Chi Minh city on June 9th 2011. The training covered C# 3.0, LINQ, C# 4.0 and Dynamic Binding.

Some pictures of the training

In a current project, I need to build a catch-all handler which could be used to wired to any static or instance delegate and event regardless of the actual delegate/event type.

For example, given the following definitions:

private delegate int Op(int i);
private delegate int BinaryOp(int i, int j);
class Test
{
    public Op OpDelegate;
    public event BinaryOp BinaryEvent;
}

I want to be able to write code like this:

obj.AddHandler("OpDelegate", args => (int)args[0] * (int)args[0]);
obj.AddHandler("BinaryEvent", args => (int)args[0] + (int)args[1]);

In the above code segment, code>obj is an instance of the Test class. AddHandler should be an extension method for object class. The parameters include the name of the delegate or event and a catch-all handler of type Func<object[], object> and this handler might have been bound to some target. In addition, the code in question mustn't need to know about the actual type of obj at compile time nor does it need to know about the actual signature of the delegate and event being wired.

What AddHandler needs to do is creating some delegate matching the definition of the delegate/event being wired and have that delegate forward the call to the Func<object[], object> argument. That calls for a bit of code generation to build a delegate instance from a runtime generated method definition (which will have its signature match the delegate/event being wired). Like when developing Fasterflect, I opt for CIL generation.

The code for the solution is below. I will incorporate it into Fasterflect as an add-on service. Note that it makes use the EmitHelper class which could be found here.

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Reflection.Emit;
using Emitter;

public static class DynamicHandler
{
    public static Type AddHandler(this Type targetType, string fieldName,
        Func<object[], object> func)
    {
        return InternalAddHandler(targetType, fieldName, func, null, true);
    }

    public static Type AssignHandler(this Type targetType, string fieldName,
        Func<object[], object> func)
    {
        return InternalAddHandler(targetType, fieldName, func, null, false);
    }

    public static Type AddHandler(this object target, string fieldName,
        Func<object[], object> func)
    {
        return InternalAddHandler(target.GetType(), fieldName, func, target, true);
    }

    public static Type AssignHandler(this object target, string fieldName,
        Func<object[], object> func)
    {
        return InternalAddHandler(target.GetType(), fieldName, func, target, false);
    }

    private static Type InternalAddHandler(Type targetType, string fieldName,
        Func<object[], object> func, object target, bool combine)
    {
        Type delegateType;
        var eventInfo = targetType.GetEvent(fieldName);
        if (eventInfo != null && !combine)
            throw new ArgumentException("AssignHandler cannot be used for event type");

        if (eventInfo != null)
        {
            delegateType = eventInfo.EventHandlerType;
            var dynamicHandler = BuildDynamicHandler(targetType, delegateType, func);
            eventInfo.GetAddMethod().Invoke(target, new Object[] {dynamicHandler});
        }
        else
        {
            var fieldInfo = targetType.Field(fieldName,
                                                target == null
                                                    ? Flags.StaticAnyVisibility
                                                    : Flags.InstanceAnyVisibility);
            var field = !combine ? null : target == null
                                            ? (Delegate) fieldInfo.Get()
                                            : (Delegate) fieldInfo.Get(target);
            delegateType = fieldInfo.FieldType;
            var dynamicHandler = BuildDynamicHandler(targetType, delegateType, func);
            field = field == null
                        ? dynamicHandler
                        : Delegate.Combine(field, dynamicHandler);
            (target ?? targetType).SetFieldValue(fieldName, field);
        }
        return delegateType;
    }

    public static Delegate BuildDynamicHandler(this Type delegateOwnerType, Type delegateType,
        Func<object[], object> func)
    {
        MethodInfo invokeMethod = delegateType.GetMethod("Invoke");
        Type returnType = invokeMethod.ReturnType;
        bool hasReturnType = returnType != Constants.VoidType;
        var paramTypes = invokeMethod.GetParameters().Select(p => p.ParameterType).ToArray();
        var dynamicMethod = new DynamicMethod("add_handler",
                                                hasReturnType ? returnType : null,
                                                new [] {typeof(Invoker)}.Concat(paramTypes).ToArray(),
                                                delegateOwnerType);
        var il = new EmitHelper(dynamicMethod.GetILGenerator());
        il.ldarg_0.end(); // <this>
        il.DeclareLocal(typeof(object[]));
        il.ldc_i4(paramTypes.Length); // <this> <length>
        il.newarr(typeof(object)); // <this> <arr>
        il.stloc_0.end(); // <this>
        for (int i = 0; i < paramTypes.Length; i++)
        {
            il.ldloc_0 // <this> <arr>
                .ldc_i4(i) // <this> <arr> <i>
                .ldarg(i + 1) // <this> <arr> <i> <arg_i+1>
                .boxIfValueType(paramTypes[i]) // <this> <arr> <i> <boxed_if_value:arg_i+1>
                .stelem_ref.end(); // <this>
        }
        il.ldloc_0.end(); // <this> <arr>
        il.callvirt(Invoker.InvokeMethodInfo); // <ret>
        if (hasReturnType)
            il.unbox_any(returnType).ret();
        else
            il.pop.ret();
        return dynamicMethod.CreateDelegate(delegateType, new Invoker(func));
    }

    public class Invoker
    {
        public static readonly MethodInfo InvokeMethodInfo =
            typeof(Invoker).Method("Invoke", Flags.InstanceAnyVisibility);
        private readonly Func<object[], object> func;

        public Invoker(Func<object[], object> func)
        {
            this.func = func;
        }

        public object Invoke(object[] args)
        {
            return func(args);
        }
    }
}

I’ve just got news from Microsoft that I am, once again, a Microsoft MVP in ASP.NET/IIS (formerly ASP/ASP.NET).  This is exciting news.  A big thanks to all Microsoft employees and community members who have worked with me in various projects during the past year.

Slides for my speech at an offline event about startups in Ho Chi Minh City.

I had a chance to speak about HTML5 in IE9 and ASP.NET MVC 3 at the Microsoft Technology Conference in Hanoi, Vietnam on Thursday Mar 17th 2011.  The event was supposed to attract 200 audiences.  However the suddenly cold weather and non-stop rain (more later) probably made a few dozens not show up.

This trip to Hanoi was very memorable in many ways.  First, I met and had conversations with many interesting people and learned many things from other speakers (agile development with Scrum & Kanban, BI in SharePoint 2010, distributed caching in practice etc.)  It’s a pity that I had to leave early to catch the flight (which was eventually delayed for as much as 2.5 hours) so I missed a couple of late sessions.

Second, the whole trip itself contains full of surprises.  Both departing and coming back flights were delayed 1 and 2.5 hours respectively, leaving me exhausted in the airports (thanks VNA!).  And then the weather.  In Ho Chi Minh, it was hot like 30 C degree something.  In Hanoi, it was 9 C the moment the plane arrived and remained that cold during the whole time.  I ended up putting on as many clothing as I brought with me to avoid catching a cold (and sounding like a duck during my speeches).  Additionally, it was raining all the time and I was basically on taxi every time I walked out of a building. (And should I mention that there were 2 cab drivers, 1 hotel receptionist and 1 flightmate mistook me for being foreigner and started speaking English to me!)

Slides and code can be found below.  There are a few pictures (of me and some other speakers) taken by a friend of mine.  I hope to receive pictures from Microsoft as well.

One of the books of which I was the technical reviewer was published: ASP.NET MVC 2 Cookbook. Access to the link to find out more about the book.

I hugely enjoyed BarCamp Saigon 2010 which took place yesterday at RMIT University.  Learned a lot of things and met great people.

Below is the slidedeck I used for my session.  Source code is here.

Last week, I conducted a training for customers of Microsoft about ASP.NET MVC 2. The training took place at Microsoft’s office in Ho Chi Minh city. The slides used for the training is below.