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…

Creating a quick Todo listing app on Windows using IIS7, Node.js and Mongodb

As I mentioned in my last post, more and more organizations are leaning towards Web Oriented Architecture (WOA) which are highly scalable. If you were exploring cool, scalable options to build highly performing web applications, you know what Node.js is for.After following the recent post from Scott Hanselman, I was up and running quickly with Node.js. In this post, I’ll explain step by step how I’ve setup Node.js and Mongodb to create a simple Todo listing application.Setting up Node.jsThis is what I’ve done.1 – Goto, scroll down and download node.exe for Windows, and place it in your c:\node folder2 – Goto IIS Node project in Git at, download the correct ‘retail’ link of IIS Node zip file (I downloaded the already built retail package, otherwise you can download and build from the source).3 – Extract the zip file some where, and run the install.bat or install_iisexpress.bat depending on your IIS Version. If you don’t have IIS in…

MVVM - Binding Multiple Radio Buttons To a single Enum Property in WPF

I had a property in my View Model, of an Enum type, and wanted to bind multiple radio buttons to this.

Firstly, I wrote a simple Enum to Bool converter, like this.

public class EnumToBoolConverter : IValueConverter { #region IValueConverter Members public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) { if (parameter.Equals(value)) return true; else return false; } public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) { return parameter; } #endregion }

And my enumeration is like

public enum CompanyTypes { Type1Comp, Type2Comp, Type3Comp } Now, in my XAML, I provided the enumeration as the ConverterParameter, of the Converter we wrote earlier, like