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。

轻松序列化对象为XML:

public static string ToXml<T>(this T obj) where T : class
{
    XmlSerializer s = new XmlSerializer(obj.GetType());
    using (StringWriter writer = new StringWriter())
    {
        s.Serialize(writer, obj);
        return writer.ToString();
    }
}

"<root><child>foo</child</root>".ToXml<MyCustomType>();

字符串。格式的快捷方式:

public static class StringExtensions
{
    // Enable quick and more natural string.Format calls
    public static string F(this string s, params object[] args)
    {
        return string.Format(s, args);
    }
}

例子:

var s = "The co-ordinate is ({0}, {1})".F(point.X, point.Y);

要快速复制粘贴，请点击这里。

难道你不觉得输入“一些字符串”. f(“param”)而不是字符串更自然吗?格式(“一些字符串”，“参数”)?

想要一个更容易读懂的名字，试试下面的建议:

s = "Hello {0} world {1}!".Fmt("Stack", "Overflow");
s = "Hello {0} world {1}!".FormatBy("Stack", "Overflow");
s = "Hello {0} world {1}!".FormatWith("Stack", "Overflow");
s = "Hello {0} world {1}!".Display("Stack", "Overflow");
s = "Hello {0} world {1}!".With("Stack", "Overflow");

..

我使用以下扩展来扩展所有的集合(也许有人发现这些有用):

/// <summary>
/// Collection Helper
/// </summary>
/// <remarks>
/// Use IEnumerable by default, but when altering or getting item at index use IList.
/// </remarks>
public static class CollectionHelper
{

    #region Alter;

    /// <summary>
    /// Swap item to another place
    /// </summary>
    /// <typeparam name="T">Collection type</typeparam>
    /// <param name="this">Collection</param>
    /// <param name="IndexA">Index a</param>
    /// <param name="IndexB">Index b</param>
    /// <returns>New collection</returns>
    public static IList<T> Swap<T>(this IList<T> @this, Int32 IndexA, Int32 IndexB)
    {
        T Temp = @this[IndexA];
        @this[IndexA] = @this[IndexB];
        @this[IndexB] = Temp;
        return @this;
    }

    /// <summary>
    /// Swap item to the left
    /// </summary>
    /// <typeparam name="T">Collection type</typeparam>
    /// <param name="this">Collection</param>
    /// <param name="Index">Index</param>
    /// <returns>New collection</returns>
    public static IList<T> SwapLeft<T>(this IList<T> @this, Int32 Index)
    {
        return @this.Swap(Index, Index - 1);
    }

    /// <summary>
    /// Swap item to the right
    /// </summary>
    /// <typeparam name="T">Collection type</typeparam>
    /// <param name="this">Collection</param>
    /// <param name="Index">Index</param>
    /// <returns>New collection</returns>
    public static IList<T> SwapRight<T>(this IList<T> @this, Int32 Index)
    {
        return @this.Swap(Index, Index + 1);
    }

    #endregion Alter;

    #region Action;

    /// <summary>
    /// Execute action at specified index
    /// </summary>
    /// <typeparam name="T">Collection type</typeparam>
    /// <param name="this">Collection</param>
    /// <param name="Index">Index</param>
    /// <param name="ActionAt">Action to execute</param>
    /// <returns>New collection</returns>
    public static IList<T> ActionAt<T>(this IList<T> @this, Int32 Index, Action<T> ActionAt)
    {
        ActionAt(@this[Index]);
        return @this;
    }

    #endregion Action;

    #region Randomize;

    /// <summary>
    /// Take random items
    /// </summary>
    /// <typeparam name="T">Collection type</typeparam>
    /// <param name="this">Collection</param>
    /// <param name="Count">Number of items to take</param>
    /// <returns>New collection</returns>
    public static IEnumerable<T> TakeRandom<T>(this IEnumerable<T> @this, Int32 Count)
    {
        return @this.Shuffle().Take(Count);
    }

    /// <summary>
    /// Take random item
    /// </summary>
    /// <typeparam name="T">Collection type</typeparam>
    /// <param name="this">Collection</param>
    /// <returns>Item</returns>
    public static T TakeRandom<T>(this IEnumerable<T> @this)
    {
        return @this.TakeRandom(1).Single();
    }

    /// <summary>
    /// Shuffle list
    /// </summary>
    /// <typeparam name="T">Collection type</typeparam>
    /// <param name="this">Collection</param>
    /// <returns>New collection</returns>
    public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> @this)
    {
        return @this.OrderBy(Item => Guid.NewGuid());
    }

    #endregion Randomize;

    #region Navigate;

    /// <summary>
    /// Get next item in collection and give first item, when last item is selected;
    /// </summary>
    /// <typeparam name="T">Collection type</typeparam>
    /// <param name="this">Collection</param>
    /// <param name="Index">Index in collection</param>
    /// <returns>Next item</returns>
    public static T Next<T>(this IList<T> @this, ref Int32 Index)
    {
        Index = ++Index >= 0 && Index < @this.Count ? Index : 0;
        return @this[Index];
    }

    /// <summary>
    /// Get previous item in collection and give last item, when first item is selected;
    /// </summary>
    /// <typeparam name="T">Collection type</typeparam>
    /// <param name="this">Collection</param>
    /// <param name="Index">Index in collection</param>
    /// <returns>Previous item</returns>
    public static T Previous<T>(this IList<T> @this, ref Int32 Index)
    {
        Index = --Index >= 0 && Index < @this.Count ? Index : @this.Count - 1;
        return @this[Index];
    }

    #endregion Navigate;

    #region Clone;

    /// <summary>
    /// 
    /// </summary>
    /// <typeparam name="T">Collection type</typeparam>
    /// <param name="this">Collection</param>
    /// <returns>Cloned collection</returns>
    public static IEnumerable<T> Clone<T>(this IEnumerable<T> @this) where T : ICloneable
    {
        return @this.Select(Item => (T)Item.Clone());
    }

    #endregion Clone;

    #region String;

    /// <summary>
    /// Joins multiple string with Separator
    /// </summary>
    /// <param name="this">Collection</param>
    /// <param name="Separator">Separator</param>
    /// <returns>Joined string</returns>
    public static String Join(this IEnumerable<String> @this, String Separator = "")
    {
        return String.Join(Separator, @this);
    }

    #endregion String;

}

我的建议:

public static bool IsNullOrEmpty(this ICollection obj)
{
  return (obj == null || obj.Count == 0);
}

使用集合和数组:

bool isNullOrEmpty = array.IsNullOrEmpty()

而不是

bool isNullOrEmpty = array == null || array.Length == 0;

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();