My Tech Blog

You get The type or namespace name Controller could not be found (are you missing a using directive or an assembly reference?) when adding a reference to an asp.net-mvc project

Wed, 09 Jan 2013 09:25:00 GMT

Have you by any chance, added a reference to an asp.net-mvc project from a Windows or Console project, and then you get:

The type or namespace name 'Controller' could not be found (are you missing a using directive or an assembly reference?)

Well the issue is fairly simple.

tl:dr : Just open project properties > Set the Target Framework to '.NET Framework 4' (or 3.5 whichever you're looking at) instead of client profile. Then Add Reference to System.Web.Mvc. And you're set :)

how to authenticate with oauth in perl (Dancer, GitHub, LWP::UserAgent)

Sat, 29 Dec 2012 16:04:17 GMT

I've been playing with perl a lot lately and after recently playing with Catalyst, I moved on to Dancer.

Dancer has a nice tutorial with a simple dummy blog application. The app is on GitHub here. It describes quite a few aspects about Dancer, including sessions, routes, storage and displaying pages.

It's a neat little example in that it's hardly a few files.

Naturally I wanted to get my hands dirty and wanted to try and implement OAuth authentication with github. I don't mean by pulling a nice CPAN module (there isn't one) but writing the whole OAuth flow myself. Fortunately I found this to be a simple task.

I managed to change the authentication in the sample dancer app to login with github. I added this in a forked project.

So I'm going to describe the following:

Use LWP::UserAgent to make requests to github
Use JSON::Parse to gather the response from GitHub
Set a session object to the username and avatar img url and use this on the masterpage (main.tt).

So you can see the forked project files. I just changed dancr.pl and main.tt. I also removed login.tt since there is no need for that. You have to add your application with github and then you'll get a client id and client secret.

Step 1 :

To login you have to redirect to https://github.com/login/oauth/authorize with the following params : YOUR CLIENT ID, redirect url, scope (these are permissions you want) and finally state which is used to prevent cross-site request forgery attacks

I added two variables on the top and the login route changes to just redirect the user to githubs login page. If the user allows your app, then github will send a special code to your app by calling your callback url.

Step 2 :

Goto your Github > Account Settings -> Applications -> Your App -> Callback Url. Note you can set this to localhost byt specifying it like this 127.0.0.1:<SOMEPORT>. I setup this url to /auth/github/callback. So in my dancr.pl I added this route, hopefully the comments should be a good explanation:

This route sub uses a helper method that looks like the following, it parses the query string into a hash.

Step 3 :

The above step adds a few session variables if all goes well, so I then use these in the main.tt page like this:

And that's about it. If all goes well your homepage should look like this:

Any comments, feedback and insults about this article are very welcome! :)

iis website is not accessible over network even though you can ping it

Wed, 19 Dec 2012 10:48:00 GMT

So you hosted your website on IIS...

..You can ping the machine it's hosted on but you can't seem to see the site.

Well, the problem is pretty simple. Most likely it's your firewall blocking

To isolate the problem quickly, it's a good idea to just shut your firewall momentarily and see if your site works.

Here are seven quick steps on how to update your firewall for IIS:

Click Start and type firewall. Find and select Windows Firewall with Advanced Security.
In the window you see, Click Inbound Rules on the right and then on the left click New Rule like so:
The wizard shows up. Select Port and click Next.
Select TCP and then choose to specify local port. Type 80. Click Next.
Select Allow the Connection. Click Next.
Check domain. Additionally you could check Private or Public if you need to host on these networks also.
Lastly, give this Inbound Rule a name and some details:

Hopefully this should get your website back up and running.

ajax upload files with asp.net-mvc and uploadify

Fri, 14 Dec 2012 10:42:00 GMT

After answering a question on stackoverflow I realized uploading files with ajax was something everyone was looking for.

So to commemorate the asp.net-mvc badge I won recently I'm writing a full example of how to do this with asp.net-mvc.

I'll use the uploadify jquery plugin. There are many others you can use too.

So all in all it's pretty simple. We'll create something that looks like this:

It allows you to select multiple files, uploads them asynchronously. Then appends a link to the file, assuming it's an image.

I uploaded a picture of my Arduino Starter Kit :)

How to :

Create a new asp.net mvc4 web application.
Delete the Index.cshtml page under \View\Home\.
Open HomeController.cs and Right Click the Index() method.
Click Add View, and uncheck Use a Layout or Master Page.

Create an upload method like the following code snippet. Your home controller should look like this:

Note : Uploadify names the file it sends as 'Filedata'.

For the view it should look like this:

Note : I had to change the css in uploadify.css, line 74 to point to the uploadify-cancel.png correctly.

74:   background: url('../Content/uploadify-cancel.png') 0 0 no-repeat;

And that's it!!! I have a full sample you can download here.

scraping images with perl

Wed, 12 Dec 2012 06:44:34 GMT

So I've been dabbling with perl lately and this is how I feel today:

See full comic here.

I'm going to go through a simple image scraping program I conjured today. I wrote this to scrape images off a t-shirt gallery so that I could help my friend make a choice on his favourite one offline. \()/ Proud to be a nerd \()/

So for perl of course there already are modules on CPAN to help. I'm using two:

WWW:Mechanize [ This is a pretty famous module and can be used for some automation, downloading content from the web etc]
HTML::TokeParser [ We'll use this to parse the html and get to the tag we want. ]

My target html looked like this:

My "algorithm" went something like:

I used WWW::Mechanize::get() to get the page I wanted.
After this I supplied the page to Html::TokerParser.
From here I went looping through all the tags using the get_tag function till I found one with the gallery-img2 class.
Then I jumped to the next img tag and got the src attribute.
And finally I used WWW::Mechanize::get to download the image for me.

The code is thoroughly commented:

Any feedback, insults and improvements are welcome! :)

How do you learn to use VIM?

Tue, 11 Dec 2012 07:38:00 GMT

So I've been slowly wading into the world of Linux/Bash/VIM/Perl, and for a windows guy it can be a murky path.

I recently took up the idea of learning VIM. Yes! It's scary! It barely works like any other text editor you're used to (on Windows especially) so here is the minimal stuff you need to know to get started:

VIM has two modes

Command Mode : Where you can do things like search/navigate etc
Insert Mode : Where you can type in text. Press the i Key to go into insert mode and ESC to get out of it.

The following shortcuts will help get you productive on VIM as a beginner:

To search press / and then type what you're looking for. n will take you to the next result and N will take you back to the previous.
Navigate up a line in command mode k
Navigate down a line in command mode j
Navigate left a character in command mode h
Navigate right a character l
To save a file :w [Press Enter] (will write to the file)
To exit without saving (in command mode) :q![Press Enter]
To Undo u
You can combine writing and quitting (in command mode): :wq [Press Enter] Or you could also do :x [Press Enter]

These shortcuts should allow you to do most things, to get turn into a power user you could look at many cheat sheets out there like this one and keep using VIM.

This is also an interesting little article you should go through:
http://cloudhead.io/2010/04/24/staying-the-hell-out-of-insert-mode/

Read this for more about this program.

CPAN doesn't install anything? Can't exec "make": No such file or directory

Mon, 26 Nov 2012 15:15:19 GMT

So you're on OSX and cpan just can't seem to install anything?

Do you see the following somewhere in your shell :

Can't exec "make": No such file or directory

Well then you're in luck, it's a plain simple fix.

You need Xcode command line tools (of course xcode itself), because make comes with it. NOTE : If you update to Mountain Lion you will need to install command line tools again! ;)

Open Xcode
Click the Xcode menu option on the top and select Preferences. (It's the Command + <comma> if xcode is focused)

You'll see the following window, click install on Command Line Tools. Once installed you're good to go! :)

You can even check if everything is ok by trying to run make on the command line:

$ make

Lastly, you can also get the Command Line Tools as a dmg for download from here:
https://developer.apple.com/downloads/index.action

But you'll need to sign in with your AppleID

solutions to sqlzoo.net More Join Operation Questions (Movie Database)

Fri, 31 Aug 2012 11:40:48 GMT

While meandering around the web for sql exercises and tutorials I came across www.sqlzoo.net.

It is the perfect place to get hands on knowledge for SQL, especially JOINS!

Below are solutions to all the questions on the More JOIN Operations tutorial. Questions 1-6 are plain straightforward. Questions 7-11 are basic join questions and 12-16 and pretty hard. I ended up spending quite some time trying to solve the last bunch.

Here are all the solutions in case you got stumped. (I just included all questions for completeness)

Problem 1 : List the films where the yr is 1962 [Show id, title]

This one is pretty straigh-forward.

Problem 2 : Give year of 'Citizen Kane'.

This one too :

Problem 3 : List all of the Star Trek movies, include the id title and yr. (All of these movies include the words Star Trek in the title.)

Problem 4 : What are the titles of the films with id 11768, 11955, 21191

Problem 5 : What id number does the actor 'Glenn Close' have?

Problem 6 : What is the id of the film 'Casablanca'

Real join questions begin :

Problem 7 : Obtain the cast list for 'Casablanca'. Use the id value that you obtained in the previous question.

Problem 8 : Obtain the cast list for the film 'Alien'

Problem 9 : List the films in which 'Harrison Ford' has appeared

Problem 10 : List the films where 'Harrison Ford' has appeared - but not in the star role. [Note: the ord field of casting gives the position of the actor. If ord=1 then this actor is in the starring role]

Problem 11: List the films together with the leading star for all 1962 films.

Hard Questions.

These questions are a little bit hard. Give some time to crack them before looking at the solutions.

Problem 12 : Which were the busiest years for 'John Travolta'. Show the number of movies he made for each year.

Problem 13 : List the film title and the leading actor for all of 'Julie Andrews' films.

Problem 14 : Obtain a list of actors in who have had at least 30 starring roles. (Yep, the result set this generates is a empty set)

Problem 15 : List the 1978 films by order of cast list size.

Problem 16 : List all the people who have worked with 'Art Garfunkel'.

And there you have it! Hope it was helpful.

Time Predict

Sun, 24 Jun 2012 13:15:00 GMT

Time Predict is finally out! I've been working on it for sometime now and bothering my friends and colleagues to test it out for me.

It's a simple application I wrote, pretty much a port of http://easyclock.appspot.com/ but it's on Android.

This app came more out of a need I myself had. Hopefully it will be useful to other people too.

Get it from the market here.

I'm very open to any Comments and Suggestions :)

How to get the current location, address and send it to a server on android

Sun, 03 Jun 2012 18:24:23 GMT

Location, Location, Location! Well this article isn't all about location.

Things I will cover in this article:

Get the location of the users device (via the NETWORK). This will be latitude and longitude.
Reverse-Geo code information from the first step and get an address
Send that off to a server via Http GET. (This is typically what you would want to do given a location ;) )

Getting a location

So first off, how do we get the users current latitude and longitude? There are two options (1) We could use the Network (2) Or the GPS. Somehow, getting a location from the network is quite accurate (I tested it a couple times) and it's fairly fast. Getting a location from the GPS then isn't too difficult.

So in a default Android application you would want to add the following permission in your AndroidManifest.xml :

<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>

This is if you're using the network, to use the GPS you would need:

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>

I have an AddressActivity.java and a main.xml. My view looks like this:

The first button gets my location and the code is below. This is pretty straightforward and the snippet is plagiarized straight from the Android docs here. I have two activity level variables lat and lon, I store the locations here so I can use them later.

To get a location from the GPS you would just change this line:

locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locationListener);

To:

locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);

Getting an Address

The magic for reverse geo-coding comes from the Geocoder class. You would need the Internet permission in your manifest and this results in an internet call.

<uses-permission android:name="android.permission.INTERNET"/>

I encapsulate all my geocoder stuff into a GetAddress() function which I call from my btnAddress. It looks like this:

Send to the Internet

Now typically when you get this far, you want to send this information off to your server somewhere and then do something useful with it. So the last function postData() sends a latitude and longitude to my server. I made little dummy program on AppHabour in ASP.NET-MVC3. It sends the data via GET through a URL.

No doubt you need the INTERNET permission as I described earlier. The code looks like this:

And there you have it!

You can download a fully runnable project of all this code from here.

Hopefully soon I will use an AsyncTask to wrap up all of this code, so it happens asynchronously.

a superfast way to search for prime numbers [sieve of eratosthenes]

Mon, 05 Mar 2012 15:52:00 GMT

I've been dabbling a little lately on pure computer science stuff like computational complexity, algorithm design and math. (And interestingly I failed high school math quite badly once)

Project Euler has been an interesting learning/practice ground : http://projecteuler.net/about

The problems here involve some math, but also deal with time complexity. If done wrong, some of the solutions to their problems could take days or longer (maybe years) to complete.

Today at problem 10 this was the case:

Find the sum of all the primes below two million.

A normal brute-force method just took way too long. On a relatively fast machine using the following method for checking for primes took nearly 22 minutes to run:

Enter- Sieve of Eratosthenes : An interestingly fast way to find primes.

You make a list of all your target numbers, in our case 1 to 2 million, then remove (or filter) all the multiples of numbers starting with two. You keep going removing multiples and your list ends up being only prime numbers.

Here's a visualization from the wikipedia article:

Here is a snippet of how I implemented it for the problem. See my whole problem solved here

Drum roll! It took ~80 millisconds to run!

I'm aching to sneak in the time to get to Level 1 which is 25 problems solved! I just got my decathlete badge today. Unfortunately the badges don't show in the little flair, they only show in your statistics page:

I'm put up all my problems as I go on github. Check it out here:
https://github.com/gideondsouza/ProjectEuler_CSharp

Hopefully this was somewhat insightful.

Resources for Learning advanced Javascript

Sun, 26 Feb 2012 16:39:40 GMT

So lately I've been trying to learn a lot of javascript. Unfortunately there are too many nuances and funky things about javascript that you probably won't find all in one place

As always learning by reading good code helps, and what better code repo to look at than the one and only dollar-sign-magic-library, JQuery!

This nifty source viewer helps you peer into jquery source :
http://james.padolsey.com/jquery/

Then there is a BRILLIANT interactive tutorial by the great John Resig:
http://ejohn.org/apps/learn/

Then there is MDN - Mozilla Developer Network, this is MSDN for the html/js developer.

Lastly here is my collection of excellent stackoverflow posts that have helped me understand javascript better:

General Javascript:

Some Jquery Posts:

If you look at the JQuery Source, the entire code is in a block like this:

(function( window, undefined ) { //all JQuery code is here })(window);

Here is a post explaining that.
What is JQuery.fn, what does is do?
Understand JQuery's JQuery.fn.init

Hopefully I'll keep updating this as I go. If you come across any interesting posts, please do share them.

A Simple tic tac toe game with QUnit, JQuery and a pure javascript engine

Wed, 08 Feb 2012 15:14:46 GMT

Yes clearly it's been done way too many times, Tic tac toe. Even worse is I haven't implemented any game AI here, in this game two (human) players play against each other.

Whats interesting about this:

I wrote a little separated engine to process the game in pure javascript.
I wrote a unit-test suite with QUNit
I hooked up the engine with the UI with JQuery (this is more obvious then interesting)

See the screenie below, keeps track of player names, game count and score:

I will (if there is any interest) put this out on github. Please do tell me if you find any mistakes in the design, structure or tests here.

HRESULT 0x80210015 when using Windows Imaging Acquisition

Tue, 31 Jan 2012 09:08:00 GMT

So if you don't know yet I have a little class library that makes scanning with a auto document feeder easy. (http://adfwia.codeplex.com/)

I recently got a couple posts under my project discussions with this error. I had a good idea what the issue was since the library is a result of a project I worked on with WIA.

Simply =>

Your scanner is not connected
Or Not supported.

Another user who posted on the aforementioned discussion, fortified this judgement when he did some research.

It's unfortunate the error has to be so arcane!!

(The project is also on github here : https://github.com/gideondsouza/AutoDocumentFeedforWIA )

Learning from seven languages in seven weeks

Thu, 01 Dec 2011 03:21:46 GMT

Lately I've been trying to break out of my MS stack shell and learn some new things. I've been writing C# now for about 5 years and using visual studio since v6 so its its been slightly hard to adapt to newer things.

Sometime ago on a Channel9 talk I heard about this book, and finally it was available in an Indian Edition (which means it's affordable)

Seven Languages in Seven Weeks: A Pragmatic Guide to Learning Programming Languages

This book is thoroughly interesting because it whizzes through seven different languages, they are : Ruby, Io, Prolog, Scala, Erlang, Clojure, Haskell

The book is divided into a section for each programming language, I'm almost through with the first one, Ruby. The author is funny and smart and most of all talks to you like a programmer. He distills the little nuances of the language and tells you what you need to know.

As I go through the book I hope to blog about each language and what I've learned.

A nifty export to CSV linq extension

Sat, 26 Nov 2011 15:05:21 GMT

So I've been using this little gem of a code snippet in quite a few apps.

Nope, I didn't come up with it on my own, I got it from this blog article:
http://mikehadlow.blogspot.com/2008/06/linq-to-csv.html

I'm not sure what exactly wasn't working but I changed something I don't quite remember.

You use it like this:

IList<AnyTypeWithProperties> tableData = ...
tableData.AsCsv();//returns the data as csv in a string.

How-To:

Add a new file into visual studio, call it 'ExportToCsvExtension.cs' or anything you want. Remember an extension method must be defined on the TOP of its namespace.

Here is the code:

Enjoy!

Abstracting reactive extensions for sql server compact and implementing an instant search

Sat, 19 Nov 2011 11:04:27 GMT

So in the last Rx article I talked about instant search. This article, we're going to go quite a few steps further and search an sql-compact-4 database asychronously! Thats right!

But! Its going to be a little head churner with lambdas and what nots, because we're going to encapsulate retreiving the data in a nice clean way(in my opinion)

You could also just:

What are we making:

You'll need the SQL CE Compact Toolbox because we are going to want an entity framework object context. (Which visual studio won't create for sqlce4 if its not a web project)

You'll also want the solution from the previous blog post on Rx.

Instructions:

Step 1 - Open the solution, open solution explorer (Ctrl + W, S). Right click the project and choose add new item. Select Data on the left and choose SQL Server Compact 4 Local Database (Phew!)

Step 2 - Its more easier to use Visual Studio's server explorer to create a new table. Open server explorer (Ctrl + W, L), it should show your database. (If it doesn't, right click connections and click add connection). Expand your database, Right click Tables and click Create Table.

Create a table like the following, note ID is an identity:

Step 3 - Throw in some data:

Step 4 - Add an entity model for your database. You'll need to have installed SQL Compact Toolbox, goto Tools>Sql Compact Toolbox, Right Click your database and click Add Entity Data Model to current project.

The code

We'll add two helper classes to abstract the task of searching our database asychronously with Rx.

So we're defining a method here that will be based on a Type T, which will be our entity object and TContext which will be the DataContext. This complete generic interface will help you later on when you want to mock and/or use DI. (I typically use MEF.)

We then implement it like so:

Notice, we'll use the T at runtime so we can use this like a repository for any entity object.

Our one and only function GetAllAsObservables, uses the ToAsync method to convert the lambda passed as an argument, into a function which returns an IObservable. We then make a call to this function getall().

We wrote ToAsync(Database1Entities, IQueryable<T>) so getall is a function that takes an instance of Database1Entities and returns an IObservable<T> which we transform/project into IObservable<IList<T>>

Our MainForm code now looks like this:

Explaination :

First off, what we did last time was, we changed the Textbox.TextChanged event to an observable sequence and throttled it by 500 milliseconds. So, our code got called by the system every 500ms, we then executed DO every time this happened.

The original SearchList function does not search asynchronously, you could try and put Thread.Sleep(5000) inside and it will block the UI.

So now!! We execute an async call through our little helper class, to search our database.

Remember our GetAllAsObservables() expects a lamba that takes our data context and returns an IQueryable<T>, this means you can pretty much run any query against your context an long as it returns the right type. Also, this runs in the context of sql, not in memory.

We get in return an IObservable<IList<T>> getfn. We then use ObserveOn because we're going to touch UI from another thread. (This is equivalent to those Invoke() calls you made in your old async code). This time on subscribe you are returned a an IList<Customer>. The lambda you pass into Subscribe is executed when the search is done async!

So try and run the code! Type in some names! =D

I hope this was useful, I'll take this further and get into how to properly abstract data access with Rx by creating Observable repositories. I've used these quite sucessfully in a number of apps!

Any critique, good, bad, ugly is welcome!

Happy Coding

Android Sdk gives failed to fetch url http://dl-ssl.google.com/.../repository.xml

Sat, 19 Nov 2011 07:16:01 GMT

Are you trying to update your Android-SDK and get:

get the “Failed to fetch URL http://dl-ssl.google.com/android/repository/repository.xml”

Searching stackoverflow suggested an internet problem of some kind, but when I tried the URL in the browser itself it didn't work.

Then I looked closer:

The SDK tools themselves have an update, so just select it and hit install.

You'll land up with a new Android SDK Manager:

Happy Coding! =)

Implementing simple instant search with Rx (Reactive Extensions)

Thu, 17 Nov 2011 19:21:00 GMT

Haven't heard of Rx, this could be a little starter tutorial for you.

Rx or Microsoft's Reactive extensions makes life simple when it comes to asychronous programming

My most favorite thing about Rx is how simple it makes instant search! A while ago I asked around on stackoverflow and just architecturing it was so difficult.

So I'm going to go through a dead simple example, where we're going to have an instant search, but, we'll have some dummy data in memory that we're going to search.

Update : I wrote a continuation of this article here where I describe instant search with Rx on a SqlCE database and a nice clean abstraction.

Here's what it'll look like:

I hope to do a post on searching real data, maybe with sql-compact 4, and then I'll get on to how to write Observable Repositories which makes life easier, especially for Silverlight!

How To:

So head over to Visual Studio and create a new form (or you can download the sample). Add a textbox and listbox like the screenshot.

We need to install Rx-Main and Rx-WinForms from nuget.

You can right click your solution and choose Manage Nuget Packages.. and search and install these.

This is the code then:

What/How/Why? :

The starting point to observables is the Observable class, the FromEventPattern method creates an observable sequence from the TextChanged event of the textbox.

Think of this like a list of notifications coming to you.

We then chain a method call to Throttle (my fav part!), it well, throttles this list of notifications by 500 milliseconds.

Here, for win-forms you need the ControlScheduler class otherwise the throttling doesn't work too well. This class comes from the Rx-WinForms package we added earlier. The Do method just does the metho you want to run, and you send off the text from the the textbox over. Lastly, calling Subscribe starts off the notifications.

Download the Sample here.(1.3MB) It's a clean solution but with the Rx nuget packages.

Hope this was useful!

Windows Cannot Find Drivers - Setting up Android USB Debugging

Sun, 13 Nov 2011 08:56:45 GMT

So if you're trying to get Android USB debugging to work with your phone and it says:

Windows Cannot find Drivers

Its probably a samsung phone? Yes?

If it is then all you have to do it install Samsung Kies and voila! You'll get everything up and running.

If you're wondering how to debug a device on your phone.

Make sure USB Debugging on your phone is turned on (Mostly under Settings>Applications>USB Debugging)
(If you have a samsung phone install Samsung Kies)
Connect your phone via USB
In eclipse : Under the Run Menu > Debug Congfigurations you should have a configuration under Android Application, if you don't double click Android Application to create a new one.
Select your configuration and then select the Target Tab.
Choose Manual then Click Debug
You will be presented with a list of your connected devices and your virtual devices.

Happy Android Programming!