Extracting the MachineSid

using System.Security.Principal;
...
string userName = Environment.MachineName + @"\Administrator";
NTAccount account= new NTAccount(userName);
SecurityIdentifier sid = (SecurityIdentifier)
     account.Translate(typeof(SecurityIdentifier));
string machineSid = sid.AccountDomainSid.ToString();

Using an ErrorProvider

1. Add it to the form

// 2. Initialise it:
errorProvider.BlinkStyle = ErrorBlinkStyle.AlwaysBlink;
errorProvider.SetIconAlignment(this, ErrorIconAlignment.MiddleRight);
errorProvider.SetIconPadding(this, 2);

// 3. To flag an error
errorProvider.SetError(tbName, "The specified user name is unknown");

// 4. To stop it flashing
errorProvider.Clear(); 

Useful Assembly Methods

using System.Reflection;


//To retrieve the version number from the 
// assembly in your code, you use can do this:
string strVersion = 
    Assembly.GetExecutingAssembly().GetName().Version.ToString(); 
//To retrieve the version number from the
// assembly that is calling your assembly, 
// you can use this:
string strVersion = 
    Assembly.GetCallingAssembly().GetName().Version.ToString();

// Retrieving the executing assembly's path as a Uri
Uri uri = new Uri(System.IO.Path.GetDirectoryName( 
      Assembly.GetExecutingAssembly().GetName().CodeBase));
// and as a string path
string path = new Uri(System.IO.Path.GetDirectoryName( 
      Assembly.GetExecutingAssembly().GetName().CodeBase)).LocalPath;

Performing FileToString and StringToFile.

The required methods are on the File class:

using System.IO;

string File.ReadAllText  (string path, Encoding enc);
string File.ReadAllText  (string path);
void   File.WriteAllText (string path, string contents, Encoding encoding);
void   File.WriteAllText (string path, string contents);

Reading and Writing Xml

#region Read/Write Xml

using System.Text;
using System.Xml;
using System.IO;

...

// Reading from XML Reader
private void FromXml(XmlReader reader)
{
   bool corrupt = false;
   while (!reader.EOF && !corrupt)
   {
       if (reader.NodeType != XmlNodeType.EndElement)
       {
           switch (reader.Name)
           {
               case "BaseElement":
                 string tmp = reader.GetAttribute("Guid");
                 m_Guid = new Guid(tmp);                    
               break;

               case "EnumType":
                  string tmp = reader.ReadElementContentAsString();
                  m_EnumType = (EnumType)Enum.Parse(
                       typeof(EnumType), tmp);
               break;
               case "Id":
                   m_Id = reader.ReadElementContentAsString();
               break;
               case "Name":
                   m_SomeThing = reader.ReadElementContentAsString();
               break;
               case "SomeDate":
                   string value = reader.ReadElementContentAsString();
                   DateTime m_SomeDate;
                   DateTime.TryParse(value, out m_SomeDate);
               break;
               default:
               break;
           }
       }
       try
       {
           reader.Read();
       }
       catch (XmlException)
       {
           corrupt = true;
       }
   }
}


// Reading from XML String
private void FromXmlString(string xml)
{
   XmlTextReader reader = new XmlTextReader(xml, XmlNodeType.Element,
       new XmlParserContext(null, new XmlNamespaceManager(
           new NameTable()), null, XmlSpace.Default));
   try
   {
       reader.MoveToContent();
       FromXml(reader);
   }
   finally
   {
       reader.Close();
   }
}

// Reading from XMLFile
public void FromXmlFile(string xmlFile)
{
   if (File.Exists(xmlFile))
   {
       XmlTextReader reader = new XmlTextReader(xmlFile);
       try
       {
           reader.MoveToContent();
           FromXml(reader);
       }
       finally
       {
           reader.Close();
       }
   }
}

// Writing to XML Writer
public void ToXml(XmlWriter writer)
{
   //m_Writer.WriteDocType("", null, null, null);
   writer.WriteStartElement("BaseElement");
   writer.WriteAttributeString("Guid", m_Guid.ToString());
   WriteContent(writer);
   writer.WriteEndElement();
   writer.Flush();
}

protected virtual void WriteContent(XmlWriter writer)
{
   writer.WriteElementString("EnumType", m_EnumType.ToString());
   writer.WriteElementString("Id", m_Id);
   writer.WriteElementString("Name", m_Name);
   writer.WriteElementString("Date", DateTime.Now.ToUniversalTime().ToString());
}

// Writing to XML String
public override string ToXmlString()
{
   StringWriter sw = new StringWriter();
   XmlTextWriter writer = new XmlTextWriter(sw);
   try
   {
       writer.Formatting = Formatting.Indented;
       writer.WriteStartDocument();
       ToXml(writer);
       writer.WriteEndDocument();
   }
   finally
   {
       writer.Close();
   }

   return sw.GetStringBuilder().ToString();
}


public void ToXmlFile(string xmlFile, Encoding encoding)
{
   XmlTextWriter writer = new XmlTextWriter(xmlFile, encoding);
   try
   {
       writer.Formatting = Formatting.Indented;
       writer.WriteStartDocument();
       ToXml(writer);
       writer.WriteEndDocument();
   }
   finally
   {
       writer.Close();
   }
}

#endregion Read/Write Xml

Basic OnPaint and OnSizeChanged Methods for a Resizable Control

// after InitializeComponent()
this.ResizeRedraw = true; // If you want resizing to cause a redraw

protected override void OnSizeChanged(EventArgs e)
{
    base.OnSizeChanged(e);
    this.Invalidate();
}

protected override void OnPaint(PaintEventArgs pea)
{
    try
    {
        pea.Graphics.FillRectangle(Brushes.DarkOliveGreen, 
new Rectangle(0, 0, Width, Height));

        // Create a new pen.
        using (Pen pen = new Pen(Brushes.Black))
        {
            // Draw a line
            Point pt1 = new Point(ClientRectangle.Left, 
ClientRectangle.Bottom - 1);
            Point pt2 = new Point(ClientRectangle.Right, 
ClientRectangle.Bottom - 1);
            pea.Graphics.DrawLine(pen, pt1, pt2);
        }

    }
    catch (Exception ex)
    {
        //TODO: Log these errors.
    }
}

Reading the Registry in c#

private static void GetMachineGuid()
{
    string machineGuid = string.Empty;
    RegistryKey rk = Registry.LocalMachine.OpenSubKey(@"Software\Microsoft\Cryptography");
    machineGuid = (string)rk.GetValue(@"MachineGuid");
    Console.WriteLine("MachineGuid: " + machineGuid);
}