Skip to main content

Rx Framework Part III - LINQ To Events - Generating GetEventName() Wrapper Methods using T4 Text Templates

Before you being, you may Read Part I and Part II 

Soon after writing my last post on LINQ to Events, I thought about creating a quick text template to automatically generate those GetEventName wrapper methods – so that we don’t end up in hand coding those GetMouseDown(), GetMouseMove() and all again. You may use it to quickly generate extension methods to create event to observable wrappers for a specific type. Here we go. Click 'view plain' to grab the source code

Add a new text file to your project, and name it EventWrapperGen.ttinclude

  //Generate the Event wrappers to create an observable from
  //an event

 //Generate a GetEventName wrapper method for events in this type
 void GenerateEventGetters(Type type)
       var events = type.GetEvents();

       foreach (var e in events)
           Type tDelegate = e.EventHandlerType;
           var parameters=GetDelegateParameterTypes(tDelegate);
			 if (parameters.Length==2 
                       && typeof(EventArgs).IsAssignableFrom(parameters[1]))

   public static IObservable<Event<<#=parameters[1].Name#>>> 
   						Get<#=e.Name#> (this <#=type.Name#> el)
       var allevents = 
           (   h => new <#=GetCorrectTypeName(tDelegate)#>(h), 
               h => el.<#=e.Name#> += h, 
               h=> el.<#=e.Name#> -= h

       return allevents;            


	//Get the parameter types for delegates
   private Type[] GetDelegateParameterTypes(Type d)
       if (d.BaseType != typeof(MulticastDelegate))
           throw new ApplicationException("Not a delegate.");

       MethodInfo invoke = d.GetMethod("Invoke");
       if (invoke == null)
           throw new ApplicationException("Not a delegate.");

       ParameterInfo[] parameters = invoke.GetParameters();
       Type[] typeParameters = new Type[parameters.Length];
       for (int i = 0; i < parameters.Length; i++)
           typeParameters[i] = parameters[i].ParameterType;
       return typeParameters;

	//Get the delegate return type
   private Type GetDelegateReturnType(Type d)
       if (d.BaseType != typeof(MulticastDelegate))
           throw new ApplicationException("Not a delegate.");

       MethodInfo invoke = d.GetMethod("Invoke");
       if (invoke == null)
           throw new ApplicationException("Not a delegate.");

       return invoke.ReturnType;
	// Fixes up a Generic Type name so that it displays properly for output.
    public static string GetCorrectTypeName(Type genericType)

			var fullTypeName=false;
            if (!genericType.IsGenericType) return genericType.Name;

            //Make sure the type is indeed generic in which case the` is in the name
            int index = genericType.Name.IndexOf("`");
            if (index == -1)
                if (!fullTypeName)
                    return genericType.Name;

                return genericType.Namespace + "." + genericType.Name;

            // Strip off the Genric postfix
            string TypeName = genericType.Name.Substring(0, index);
            string formatted = TypeName;

            //Parse the generic type arguments
            Type[] genericArgs = genericType.GetGenericArguments();
            string genericOutput = "<";
            bool Start = true;
            foreach (Type arg in genericArgs)
                if (Start)
                    genericOutput += arg.Name;
                    Start = false;
                    genericOutput += "," + arg.Name;

            genericOutput += ">";
            formatted += genericOutput;

            if (!fullTypeName)
                return formatted;
            return genericType.Namespace + "." + formatted;

And now, add a new tt file to your project, and import the above include file as below. Make sure the Custom Tool property of the tt file is set to TextTemplatingFileGenerator.
<#@ template 
language="C#v3.5" debug="true" hostSpecific="true" #>
<#@ output extension=".cs" #>
<#@ Assembly Name="System.dll" #>
<#@ Assembly Name="System.Core.dll" #>
<#@ Assembly Name="System.Windows.Forms.dll" #>
<#@ Assembly Name="WindowsBase.dll" #>
<#@ Assembly Name="PresentationFramework.dll" #>
<#@ Assembly Name="PresentationCore.dll" #>
<#@ import namespace="System" #>
<#@ import namespace="System.IO" #>
<#@ import namespace="System.Diagnostics" #>
<#@ import namespace="System.Linq" #>
<#@ import namespace="System.Collections" #>
<#@ import namespace="System.Windows" #>
<#@ import namespace="System.Windows.Controls" #>
<#@ import namespace="System.Reflection" #>
<#@ import namespace="System.Collections.Generic" #> 

<#@include file="EventWrapperGen.ttinclude" #>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Reflection;
using System.Diagnostics;

namespace ReactiveExtensions 

public static class <#=typeof(UIElement).Name#>Extensions 




You can replace the UIElement type above with any type, to generate the related extension methods. If you havn’t yet done, Read Part I and Part II as well.  Enjoy Coding!!

Shout it

Popular posts from this blog

Top 7 Coding Standards & Guideline Documents For C#/.NET Developers

Some time back, I collated a list of 7 Must Read, Free EBooks for .NET Developers, and a lot of people found it useful. So, I thought about putting together a list of Coding Standard guidelines/checklists for .NET /C# developers as well.As you may already know, it is easy to come up with a document - the key is in implementing these standards in your organization, through methods like internal trainings, Peer Reviews, Check in policies, Automated code review tools etc. You can have a look at FxCop and/or StyleCop for automating the review process to some extent, and can customize the rules based on your requirements.Anyway, here is a list of some good Coding Standard Documents. They are useful not just from a review perspective - going through these documents can definitely help you and me to iron out few hidden glitches we might have in the programming portion of our brain. So, here we go, the listing is not in any specific order.1 – IDesign C# Coding StandardsIDesign C# coding stand…

5 Awesome Learning Resources For Programmers (To help you and your kids to grow the geek neurons)

Happy New Year, this is my first post in 2012. I’ll be sharing few awesome learning resources I’ve bookmarked, and will be pointing out some specific computer/programming related courses I've found interesting from these resources.Also, thought about saving this blog post for my kids as well - instead of investing in these Child education schemes (though they are too small as of today, 2 years and 60 days respectively ). Anyway, personally my new year resolution is to see as much videos from this course collections (assuming I can find some free time in between my regular job && changing my babies diapers).1 – Khan AcademyAs I mentioned some time back, you and your kids are missing some thing huge if you havn’t heard about Khan Academy.  It is an awesome learning resource, especially if you want to re-visit your basics in Math, Science etc.With a library of over 2,600 videos covering everything from arithmetic to physics, finance, and history and 268 practice exercises, th…

Hack Raspberry Pi – How To Build Apps In C#, WinForms and ASP.NET Using Mono In Pi

Recently I was doing a bit of R&D related to finding a viable, low cost platform for client nodes. Obviously, I came across Raspberry Pi, and found the same extremely interesting. Now, the missing piece of the puzzle was how to get going using C# and .NET in the Pi. C# is a great language, and there are a lot of C# developers out there in the wild who are interested in the Pi.In this article, I’ll just document my findings so far, and will explain how develop using C# leveraging Mono in a Raspberry Pi. Also, we’ll see how to write few minimal Windows Forms & ASP.NET applications in the Pie as well.Step 1: What is Raspberry Pi?Raspberry Pi is an ARM/Linux box for just ~ $30. It was introduced with a vision to teach basic computer science in schools. How ever, it got a lot of attention from hackers all around the world, as it is an awesome low cost platform to hack and experiment cool ideas as Pi is almost a full fledged computer.  More About R-Pi From Wikipedia.The Raspberry Pi