C# Basics: Extension Methods and QDD vs TDD

by Tyler Jensen 27. September 2011 13:17

In this sixth installment of C# Basics, I want to share a brief snippet of an extension method I’ve found useful that will introduce you to QDD as well. Quick and Dirty Design (QDD) is my name for having multiple tiny console application projects lying around in which I test little code snippets before putting them into something more serious. This is only necessary in projects in which TDD has not been used and no testing framework or tests are available for whatever reason.

But back to extension methods. From MSDN we learn:

“Extension methods enable you to "add" methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type. Extension methods are a special kind of static method, but they are called as if they were instance methods on the extended type. For client code written in C# and Visual Basic, there is no apparent difference between calling an extension method and the methods that are actually defined in a type.”

As the MSDN article points out, the most common extension methods you may run into are the LINQ standard query operations. But don’t let that stop you from providing yourself with some very nice little extension methods like this one:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Text.RegularExpressions;

namespace IOTest
{
  class Program
  {
    static void Main(string[] args)
    {
      string phone1 = @"8015551212";
      string phone2 = @"(8a0d1d)d d5d5d5d-d1d2d1d2";

      if (phone1.StripNonNumeric() == phone2.StripNonNumeric())
        Console.WriteLine("true");
      else
        Console.WriteLine("false");

      Console.ReadLine();
    }
  }

  static class Ext
  {
    private static Regex nonNum = new Regex(@"[^0-9]");

    public static string StripNonNumeric(this string item)
    {
      return nonNum.Replace(item, string.Empty);
    }
  }
}

Tags:

C# Basics | Code | Software Development

“Come What May, And Love It” (and Learn to Laugh)

by Tyler Jensen 26. September 2011 00:50

I remember listening to this wise counsel three years ago from Elder Joseph B. Wirthlin Of the Quorum of the Twelve Apostles. Today my mother reminded me of it and I enjoyed reading it again. If you have ever faced tough times or felt like you were on the losing end of a game, in sport, in work, in life, I hope this article will pick you up.

I would like to highlight one of the points Elder Wirthlin makes, perhaps my favorite:

Learn to laugh – When things go wrong, we can choose to be angry or sad or depressed, but if we choose to laugh, we can get through the present difficulty and more easily find a solution.

“The next time you’re tempted to groan, you might try to laugh instead. It will extend your life and make the lives of all those around you more enjoyable.”

When the stresses of work or a commute or a family crisis threaten to bring you down, laugh. It truly is the best medicine!

Tags:

Commentary | Personal

C# Basics: Symmetric Encryption with Rijndael

by Tyler Jensen 23. September 2011 03:01

I often need to encrypt a string and then decrypt it. Sometimes its to move some value from one server to another without the benefit of SSL. So for the fifth installment of C# Basics, I’ll share the a generic version of a little encryption utility I’ve used many times and in many places.

Most Important: If you decide to use this code, be sure to change the key and vector text to something only you know. You might even want to use a hardware security module.

I like AES (formerly known as Rijndael, pronounced “rain-doll”) but you can pick your own algorithm. The code below will work with most of the .NET symmetric encryption algorithms.

using System;
using System.Security.Cryptography;
using System.Text;

namespace MyCrypt
{
  public static class Tokenizer
  {
    //create your own unique key and vector strings
    //maybe even lock them up and require a cert to get them out
    private const string keyText = @"The quick brown fox jumps";
    private const string vectorText = @"over the lazy dog.";
    private static byte[] key = null;
    private static byte[] vector = null;

    static Tokenizer()
    {
      key = GetMD5Hash(keyText);
      vector = GetMD5Hash(vectorText);
    }

    public static string Encrypt(string val)
    {
      if (string.IsNullOrWhiteSpace(val)) return null;
      RijndaelManaged rjm = new RijndaelManaged();
      rjm.KeySize = 128;
      rjm.BlockSize = 128;
      rjm.Key = key;
      rjm.IV = vector;
      byte[] input = Encoding.UTF8.GetBytes(val);
      byte[] output = rjm.CreateEncryptor()
        .TransformFinalBlock(input, 0, input.Length);
      string data = Convert.ToBase64String(output);
      return data;
    }

    public static string Decrypt(string val)
    {
      if (string.IsNullOrWhiteSpace(val)) return null;
      try
      {
        RijndaelManaged rjm = new RijndaelManaged();
        rjm.KeySize = 128;
        rjm.BlockSize = 128;
        rjm.Key = key;
        rjm.IV = vector;
        byte[] input = Convert.FromBase64String(val);
        byte[] output = rjm.CreateDecryptor()
          .TransformFinalBlock(input, 0, input.Length);
        string data = Encoding.UTF8.GetString(output);
        return data;
      }
      catch
      {
        return null;
      }
    }

    static byte[] GetMD5Hash(string data)
    {
      MD5 md5 = MD5CryptoServiceProvider.Create();
      return md5.ComputeHash(Encoding.UTF8.GetBytes(data));
    }
  }
}

Tags:

C# Basics | Code | Software Development

Keystrokes – Don’t Waste Them

by Tyler Jensen 21. September 2011 04:18

I spend perhaps six hours a day, five days a week, fifty weeks a year hitting the keys. At my slow average typing speed of 30 words per minute (I can type faster but I’m not constantly hitting the keys, so I’m guessing here) and assuming I spend thirty years of my life doing this, my total keystrokes (assuming an average of 6 keystrokes per word) will be:

60 minutes * 6 hours * 5 days * 50 weeks * 30 years * 30 words * 6 keystrokes = 16,200,000 keystrokes

Percentage of my work output firing off an ill conceived email providing advice to someone who does not care or want the advice and will certainly not waste time reading the missive: 0.01%

Today I wasted 0.01% of my available productivity.

I’ve already consumed nearly 50% of my available keystrokes, so I’m posting this to remind myself to conserve my energy and use what remains of my personal utility more wisely.

Important note to self. Do not waste time writing perfectly good advice and sending it to someone who could not care less about your opinion. Instead, read a good book. Write a new blog post. Refactor some old code. Or just watch the leaves in the trees dance in the wind. This would be a more valuable use of that time. Time that cannot ever be recaptured.

Tags:

Commentary | Personal

C# Basics: If-Else If-Else vs Switch vs Dictionary<K,T> in Dealing with Multiple Choices

by Tyler Jensen 20. September 2011 00:12

In this fourth installment of C# Basics, let’s take a look at how you handle multiple choice questions in your code. When you need to decide on a course of action based on the multiple possible values a variable may have, you have three essential choices.

  1. if | else if … | else
  2. switch
  3. Dictionary<K,T>

The code below shows you an example of each:

public class DownloadViewModel
{
  public Byte[] Contents { get; set; }
  public string FileName { get; set; }

  public string ContentType1
  {
    get
    {
      string ext = Path.GetExtension(FileName).ToLower();
      if (ext == ".pdf")
        return "application/pdf";
      else if (ext == ".txt")
        return "application/txt";
      else  
        return "application/octet-stream";
    }
  }

  public string ContentType2
  {
    get
    {
      switch (Path.GetExtension(FileName).ToLower())
      {
        case ".pdf":
          return "application/pdf";
        case ".txt":
          return "application/txt";
        default:
          return "application/octet-stream";
      }
    }
  }

  public string ContentType3
  {
    get
    {
      if (map.Count == 0) LoadMap();
      string val = string.Empty;
      if (!map.TryGetValue(Path.GetExtension(FileName).ToLower(), out val))
      {
        val = "application/octet-stream";
      }
      return val;
    }
  }

  private void LoadMap()
  {
    map.Add(".pdf", "application/pdf");
    map.Add(".txt", "application/txt");
    map.Add("*.*", "application/octet-stream");
  }

  private Dictionary<string, string> map = new Dictionary<string, string>();
}

So how do you pick which one to use? For me, the choice is easy. If I have only a few possible values that are not likely to change, I’ll use the if|else if|else construct. If I have a fair number (more than 3 and less than 16) and these values are not likely to change, I’ll use the switch statement. But if the values are likely to change or be data driven or if the number of values is greater than 15, I prefer to use a Dictionary.

Another highly valuable use of the Dictionary is when the values will kick off some action that may be lengthy or complicated. In that case, I prefer a Dictionary<T, ActionForT>. I can then retrieve the ActionForT and call the Execute method. Like this:

public class DownloadModel
{
  public Byte[] Contents { get; set; }
  public string FileName { get; set; }

  public string ContentType
  {
    get
    {
      string ext = Path.GetExtension(FileName).ToLower();
      if (ext == ".pdf")
        return "application/pdf";
      else if (ext == ".txt")
        return "application/txt";
      else  
        return "application/octet-stream";
    }
  }

  public void Save()
  {
    if (map.Count == 0) LoadMap();
    Action action = null;
    if (map.TryGetValue(Path.GetExtension(FileName).ToLower(), out action))
    {
      action(); //execute the action stored in our map
    }
    else
    {
      map["*.*"](); //execute the default action
    }
  }

  private void SavePdf()
  {
    throw new NotImplementedException();
  }

  private void SaveTxt()
  {
    throw new NotImplementedException();
  }

  private void SaveOther()
  {
    throw new NotImplementedException();
  }

  private void LoadMap()
  {
    map.Add(".pdf", new Action(SavePdf));
    map.Add(".txt", new Action(SaveTxt));
    map.Add("*.*", new Action(SaveOther));
  }

  private Dictionary<string, Action> map = new Dictionary<string, Action>();
}

Tags:

C# Basics | Code | Software Development

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Tyler Jensen

Tyler Jensen
.NET Developer and Architect

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