Skip to main content

AutoCommand For MVVM – More tricks With Lambdas and CallerMemberName

imageFew days back I ranted about Lamdba Patterns in C# and Init Time branching.  I also had a generally insane example regarding Init Time branching using CallerMemberName attribute, and got few comments about the usefulness (or the lack of the same).

While I generally agree with the comments, here is a may be useful, still crazy AutoCommand for your next basement MVVM application. First, here is how the AutoCommand will work.


//Our simple View Model
public class SimpleMathViewModel : BaseViewModel
        public SimpleMathViewModel()
            Commands = new Dictionary<string, Action>
                    {"Add", ()=>Result=A+B},
                    {"Substract", ()=>Result=A-B},
                    {"Multiply", ()=>Result=A*B},
                    {"Divide", ()=>Result=A/B}

        //Your commands should get automatically wired up

        public ICommand Add { get { return new AutoCommand(this); } }
        public ICommand Substract { get { return new AutoCommand(this); } }
        public ICommand Multiply { get { return new AutoCommand(this); } }
        public ICommand Divide { get { return new AutoCommand(this); } }

        //Other blah blah properties
        public int A { get; set; }
        public int B { get; set; }

        private int _result;
        public int Result
            get { return _result; }
                _result = value; OnPropertyChanged();

Also, Look ma, there is no dirty property name string in the OnPropertyChanged method call to raise the PropertyChanged notification as it is inferred  - but I'm sure you might have read some where else how to use CallerMemberName to do the trick. If you are still wondering, see the method implementation in the BaseViewModel code below.

Leaving that aside – how’z the wiring works for AutoCommand? Alright, guess you guessed it. Here is the AutoCommand implementation.

   public class AutoCommand : ICommand
        private readonly BaseViewModel _instance;
        private readonly string _caller;

        //Just keep the caller name and the base view model instance
        public AutoCommand(BaseViewModel instance, 
                [CallerMemberName]string caller = "")
            _instance = instance;
            _caller = caller;

        public bool CanExecute(object parameter)
            return true; //who cares

        //Fetch the right command to execute from the dictionary
        public void Execute(object parameter)
            _instance.Commands[_caller](); //get the ICommand based on the caller name

        public event EventHandler CanExecuteChanged;


And if you are wondering how we've implemented the BaseViewModel, it is trivial. There only interesting piece there is how we inject the property name to the base class method.

 public abstract class BaseViewModel : INotifyPropertyChanged
        public event PropertyChangedEventHandler PropertyChanged;
        public Dictionary<string, Action> Commands { get; set; }

        protected virtual void OnPropertyChanged([CallerMemberName]string propertyName="")
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));

This is not a best practice show case, was just discussing a language feature and few possibilities. Happy and Insane coding Smile

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…

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…