这是我写的唯一一个我经常使用的扩展。 它使得用System.Net.Mail发送电子邮件更容易一些。

public static class MailExtension
{
    // GetEmailCreditial(out strServer) gets credentials from an XML file
    public static void Send(this MailMessage email)
    {
        string strServer = String.Empty;
        NetworkCredential credentials = GetEmailCreditial(out strServer);
        SmtpClient client = new SmtpClient(strServer) { Credentials = credentials };
        client.Send(email);
    }

    public static void Send(this IEnumerable<MailMessage> emails)
    {
        string strServer = String.Empty;
        NetworkCredential credentials = GetEmailCreditial(out strServer);
        SmtpClient client = new SmtpClient(strServer) { Credentials = credentials };
        foreach (MailMessage email in emails)
            client.Send(email);
    }
}

// Example of use: 
new MailMessage("info@myDomain.com","you@gmail.com","This is an important Subject", "Body goes here").Send();
//Assume email1,email2,email3 are MailMessage objects
new List<MailMessage>(){email1, email2, email}.Send();

将double类型转换为使用指定区域性格式化的字符串:

public static class ExtensionMethods 
{
  public static string ToCurrency(this double value, string cultureName)
  {
    CultureInfo currentCulture = new CultureInfo(cultureName);
    return (string.Format(currentCulture, "{0:C}", value));
  }
}

例子:

double test = 154.20;
string testString = test.ToCurrency("en-US"); // $154.20

The Substring method on the string class has always felt inadequate to me. Usually when you do a substring, you know the character(s) from where you want to start, and the charachter(s) where you want to end. Thus, I've always felt that have to specify length as the second parameter is stupid. Therefore, I've written my own extension methods. One that takes a startIndex and an endIndex. And one, that takes a startText (string) and endText (string) so you can just specify the text from where to start the substring, and the text for where to end it.

注意:我不能将方法命名为。net中的Substring，因为我的第一个重载采用了与。net重载中的一个相同的参数类型。因此我将它们命名为Subsetstring。请随意添加到CodePlex…

public static class StringExtensions
{
    /// <summary>
    /// Returns a Subset string starting at the specified start index and ending and the specified end
    /// index.
    /// </summary>
    /// <param name="s">The string to retrieve the subset from.</param>
    /// <param name="startIndex">The specified start index for the subset.</param>
    /// <param name="endIndex">The specified end index for the subset.</param>
    /// <returns>A Subset string starting at the specified start index and ending and the specified end
    /// index.</returns>
    public static string Subsetstring(this string s, int startIndex, int endIndex)
    {
        if (startIndex > endIndex)
        {
            throw new InvalidOperationException("End Index must be after Start Index.");
        }

        if (startIndex < 0)
        {
            throw new InvalidOperationException("Start Index must be a positive number.");
        }

        if(endIndex <0)
        {
            throw new InvalidOperationException("End Index must be a positive number.");
        }

        return s.Substring(startIndex, (endIndex - startIndex));
    }

    /// <summary>
    /// Finds the specified Start Text and the End Text in this string instance, and returns a string
    /// containing all the text starting from startText, to the begining of endText. (endText is not
    /// included.)
    /// </summary>
    /// <param name="s">The string to retrieve the subset from.</param>
    /// <param name="startText">The Start Text to begin the Subset from.</param>
    /// <param name="endText">The End Text to where the Subset goes to.</param>
    /// <param name="ignoreCase">Whether or not to ignore case when comparing startText/endText to the string.</param>
    /// <returns>A string containing all the text starting from startText, to the begining of endText.</returns>
    public static string Subsetstring(this string s, string startText, string endText, bool ignoreCase)
    {
        if (string.IsNullOrEmpty(startText) || string.IsNullOrEmpty(endText))
        {
            throw new ArgumentException("Start Text and End Text cannot be empty.");
        }
        string temp = s;
        if (ignoreCase)
        {
            temp = s.ToUpperInvariant();
            startText = startText.ToUpperInvariant();
            endText = endText.ToUpperInvariant();
        }
        int start = temp.IndexOf(startText);
        int end = temp.IndexOf(endText, start);
        return Subsetstring(s, start, end);
    }
}

用法:

string s = "This is a tester for my cool extension method!!";
       s = s.Subsetstring("tester", "cool",true);

输出:"test for my "

// Values ordered true/false
// True/false values separated by a capital letter
// Only two values allowed
// ---------------------------
// Limited, but could be useful
public enum BooleanFormat
{
    OneZero,
    YN,
    YesNo,
    TF,
    TrueFalse,
    PassFail,
    YepNope
}

public static class BooleanExtension
{
    /// <summary>
    /// Converts the boolean value of this instance to the specified string value. 
    /// </summary>
    private static string ToString(this bool value, string passValue, string failValue)
    {
        return value ? passValue : failValue;
    }

    /// <summary>
    /// Converts the boolean value of this instance to a string. 
    /// </summary>
    /// <param name="booleanFormat">A BooleanFormat value. 
    /// Example: BooleanFormat.PassFail would return "Pass" if true and "Fail" if false.</param>
    /// <returns>Boolean formatted string</returns>
    public static string ToString(this bool value, BooleanFormat booleanFormat)
    {
        string booleanFormatString = Enum.GetName(booleanFormat.GetType(), booleanFormat);
        return ParseBooleanString(value, booleanFormatString);      
    }

    // Parses boolean format strings, not optimized
    private static string ParseBooleanString(bool value, string booleanFormatString)
    {
        StringBuilder trueString = new StringBuilder();
        StringBuilder falseString = new StringBuilder();

        int charCount = booleanFormatString.Length;

        bool isTrueString = true;

        for (int i = 0; i != charCount; i++)
        {
            if (char.IsUpper(booleanFormatString[i]) && i != 0)
                isTrueString = false;

            if (isTrueString)
                trueString.Append(booleanFormatString[i]);
            else
                falseString.Append(booleanFormatString[i]);
        }

        return (value == true ? trueString.ToString() : falseString.ToString());
    }

还有一点:

public enum ParseFailBehavior
{
   ReturnNull,
   ReturnDefault,
   ThrowException
}

public static T? ParseNullableEnum<T>(this string theValue, ParseFailBehavior desiredBehavior = ParseFailBehavior.ReturnNull) where T:struct
{
   T output;
   T? result = Enum.TryParse<T>(theValue, out output) 
      ? (T?)output
      : desiredBehavior == ParseFailBehavior.ReturnDefault
         ? (T?)default(T)
         : null;

   if(result == null && desiredBehavior == ParseFailBehavior.ThrowException)
      throw new ArgumentException("Parse Failed for value {0} of enum type {1}".
         FormatWith(theValue, typeof(T).Name));       
}

这个版本需要。net 4.0;在3.5中你没有TryParse和可选参数;你就只能使用enumel . parse()，你必须尝试捕获它。它在3.5中仍然是完全可行的(而且更有用，因为enumel . parse()是oogly的，也是你唯一的其他选择):

public static T? ParseNummableEnum<T>(this string theValue)
{
    return theValue.ParseNullableEnum<T>(ParseFailBehavior.ReturnNull);
}

public static T? ParseNullableEnum<T>(this string theValue, 
    ParseFailBehavior desiredBehavior) where T:struct
{
    try
    {
        return (T?) Enum.Parse(typeof (T), theValue);
    }
    catch (Exception)
    {
        if(desiredBehavior == ParseFailBehavior.ThrowException) throw;
    }

    return desiredBehavior == ParseFailBehavior.ReturnDefault ? (T?)default(T) : null;
}

用法:

//returns null if OptionOne isn't an enum constant
var myEnum = "OptionOne".ParseNullableEnum<OptionEnum>(); 

//guarantees a return value IF the enum has a "zero" constant value (generally a good practice)
var myEnum = "OptionTwo".ParseNullableEnum<OptionEnum>(ParseFailBehavior.ReturnDefault).Value 

我最常用的扩展是一个可以格式化字节数组:

/// <summary>
/// Returns a string representation of a byte array.
/// </summary>
/// <param name="bytearray">The byte array to represent.</param>
/// <param name="subdivision">The number of elements per group,
/// or 0 to not restrict it. The default is 0.</param>
/// <param name="subsubdivision">The number of elements per line,
/// or 0 to not restrict it. The default is 0.</param>
/// <param name="divider">The string dividing the individual bytes. The default is " ".</param>
/// <param name="subdivider">The string dividing the groups. The default is "  ".</param>
/// <param name="subsubdivider">The string dividing the lines. The default is "\r\n".</param>
/// <param name="uppercase">Whether the representation is in uppercase hexadecimal.
/// The default is <see langword="true"/>.</param>
/// <param name="prebyte">The string to put before each byte. The default is an empty string.</param>
/// <param name="postbyte">The string to put after each byte. The default is an empty string.</param>
/// <returns>The string representation.</returns>
/// <exception cref="ArgumentNullException">
/// <paramref name="bytearray"/> is <see langword="null"/>.
/// </exception>
public static string ToArrayString(this byte[] bytearray,
    int subdivision = 0,
    int subsubdivision = 0,
    string divider = " ",
    string subdivider = "  ",
    string subsubdivider = "\r\n",
    bool uppercase = true,
    string prebyte = "",
    string postbyte = "")
{
    #region Contract
    if (bytearray == null)
        throw new ArgumentNullException("bytearray");
    #endregion

    StringBuilder sb = new StringBuilder(
        bytearray.Length * (2 + divider.Length + prebyte.Length + postbyte.Length) +
        (subdivision > 0 ? (bytearray.Length / subdivision) * subdivider.Length : 0) +
        (subsubdivision > 0 ? (bytearray.Length / subsubdivision) * subsubdivider.Length : 0));
    int groupElements = (subdivision > 0 ? subdivision - 1 : -1);
    int lineElements = (subsubdivision > 0 ? subsubdivision - 1 : -1);
    for (long i = 0; i < bytearray.LongLength - 1; i++)
    {
        sb.Append(prebyte);
        sb.Append(String.Format(CultureInfo.InvariantCulture, (uppercase ? "{0:X2}" : "{0:x2}"), bytearray[i]));
        sb.Append(postbyte);

        if (lineElements == 0)
        {
            sb.Append(subsubdivider);
            groupElements = subdivision;
            lineElements = subsubdivision;
        }
        else if (groupElements == 0)
        {
            sb.Append(subdivider);
            groupElements = subdivision;
        }
        else
            sb.Append(divider);

        lineElements--;
        groupElements--;
    }
    sb.Append(prebyte);
    sb.Append(String.Format(CultureInfo.InvariantCulture, (uppercase ? "{0:X2}" : "{0:x2}"), bytearray[bytearray.LongLength - 1]));
    sb.Append(postbyte);

    return sb.ToString();
}

默认情况下，ToArrayString()只是将字节数组打印为由单个字节组成的长字符串。但是，ToArrayString(4,16)将字节分组为4个一组，一行16个字节，就像在您最喜欢的十六进制编辑器中一样。下面很好地格式化了字节数组，以便在c#代码中使用:

byte[] bytearray = new byte[]{ ... };
Console.Write(bytearray.ToArrayString(4, 16, ", ", ",   ", ",\r\n", true, "0x"));

这是我写的，所以你可以用Codeplex。