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;

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 

把这个:

DbCommand command = connection.CreateCommand();
command.CommandText = "SELECT @param";

DbParameter param = command.CreateParameter();
param.ParameterName = "@param";
param.Value = "Hello World";

command.Parameters.Add(param);

．.． 到这个:

DbCommand command = connection.CreateCommand("SELECT {0}", "Hello World");

．.． 使用这个扩展方法:

using System;
using System.Data.Common;
using System.Globalization;
using System.Reflection;

namespace DbExtensions {

   public static class Db {

      static readonly Func<DbConnection, DbProviderFactory> getDbProviderFactory;
      static readonly Func<DbCommandBuilder, int, string> getParameterName;
      static readonly Func<DbCommandBuilder, int, string> getParameterPlaceholder;

      static Db() {

         getDbProviderFactory = (Func<DbConnection, DbProviderFactory>)Delegate.CreateDelegate(typeof(Func<DbConnection, DbProviderFactory>), typeof(DbConnection).GetProperty("DbProviderFactory", BindingFlags.Instance | BindingFlags.NonPublic).GetGetMethod(true));
         getParameterName = (Func<DbCommandBuilder, int, string>)Delegate.CreateDelegate(typeof(Func<DbCommandBuilder, int, string>), typeof(DbCommandBuilder).GetMethod("GetParameterName", BindingFlags.Instance | BindingFlags.NonPublic, Type.DefaultBinder, new Type[] { typeof(Int32) }, null));
         getParameterPlaceholder = (Func<DbCommandBuilder, int, string>)Delegate.CreateDelegate(typeof(Func<DbCommandBuilder, int, string>), typeof(DbCommandBuilder).GetMethod("GetParameterPlaceholder", BindingFlags.Instance | BindingFlags.NonPublic, Type.DefaultBinder, new Type[] { typeof(Int32) }, null));
      }

      public static DbProviderFactory GetProviderFactory(this DbConnection connection) {
         return getDbProviderFactory(connection);
      }

      public static DbCommand CreateCommand(this DbConnection connection, string commandText, params object[] parameters) {

         if (connection == null) throw new ArgumentNullException("connection");

         return CreateCommandImpl(GetProviderFactory(connection).CreateCommandBuilder(), connection.CreateCommand(), commandText, parameters);
      }

      private static DbCommand CreateCommandImpl(DbCommandBuilder commandBuilder, DbCommand command, string commandText, params object[] parameters) {

         if (commandBuilder == null) throw new ArgumentNullException("commandBuilder");
         if (command == null) throw new ArgumentNullException("command");
         if (commandText == null) throw new ArgumentNullException("commandText");

         if (parameters == null || parameters.Length == 0) {
            command.CommandText = commandText;
            return command;
         }

         object[] paramPlaceholders = new object[parameters.Length];

         for (int i = 0; i < paramPlaceholders.Length; i++) {

            DbParameter dbParam = command.CreateParameter();
            dbParam.ParameterName = getParameterName(commandBuilder, i);
            dbParam.Value = parameters[i] ?? DBNull.Value;
            command.Parameters.Add(dbParam);

            paramPlaceholders[i] = getParameterPlaceholder(commandBuilder, i);
         }

         command.CommandText = String.Format(CultureInfo.InvariantCulture, commandText, paramPlaceholders);

         return command;
      }
   }
}

更多的麻烦。NET扩展方法:DbExtensions

我最喜欢的是字符串上的IsLike()扩展。IsLike()匹配VB的Like操作符，当你不想写一个完整的正则表达式来解决你的问题时，它很方便。用法是这样的:

"abc".IsLike("a*"); // true
"Abc".IsLike("[A-Z][a-z][a-z]"); // true
"abc123".IsLike("*###"); // true
"hat".IsLike("?at"); // true
"joe".IsLike("[!aeiou]*"); // true

"joe".IsLike("?at"); // false
"joe".IsLike("[A-Z][a-z][a-z]"); // false

下面是代码

public static class StringEntentions {
    /// <summary>
    /// Indicates whether the current string matches the supplied wildcard pattern.  Behaves the same
    /// as VB's "Like" Operator.
    /// </summary>
    /// <param name="s">The string instance where the extension method is called</param>
    /// <param name="wildcardPattern">The wildcard pattern to match.  Syntax matches VB's Like operator.</param>
    /// <returns>true if the string matches the supplied pattern, false otherwise.</returns>
    /// <remarks>See http://msdn.microsoft.com/en-us/library/swf8kaxw(v=VS.100).aspx</remarks>
    public static bool IsLike(this string s, string wildcardPattern) {
        if (s == null || String.IsNullOrEmpty(wildcardPattern)) return false;
        // turn into regex pattern, and match the whole string with ^$
        var regexPattern = "^" + Regex.Escape(wildcardPattern) + "$";

        // add support for ?, #, *, [], and [!]
        regexPattern = regexPattern.Replace(@"\[!", "[^")
                                   .Replace(@"\[", "[")
                                   .Replace(@"\]", "]")
                                   .Replace(@"\?", ".")
                                   .Replace(@"\*", ".*")
                                   .Replace(@"\#", @"\d");

        var result = false;
        try {
            result = Regex.IsMatch(s, regexPattern);
        }
        catch (ArgumentException ex) {
            throw new ArgumentException(String.Format("Invalid pattern: {0}", wildcardPattern), ex);
        }
        return result;
    }
}

我已经实现了一个扩展方法包(在http://foop.codeplex.com/上可用)，其中一些是我日常使用的:

// the most beloved extension method for me is Pipe:
<%= variable.Pipe(x => this.SomeFunction(x)).Pipe(y =>
{
    ...;
    return this.SomeOtherFunction(y);
}) %>

var d = 28.December(2009); // some extension methods for creating DateTime
DateTime justDatePart = d.JustDate();
TimeSpan justTimePart = d.JustTime();
var nextTime = d.Add(5.Hours());

using(StreamReader reader = new StreamReader("lines-of-data-file-for-example")) {
    ...
    // for reading streams line by line and usable in LINQ
    var query = from line in reader.Lines(); 
                where line.Contains(_today)
                select new { Parts = PartsOf(line), Time = _now };
}

500.Sleep();

XmlSerialize and XmlDeserialize

IsNull and IsNotNull

IfTrue, IfFalse and Iff:
true.IfTrue(() => Console.WriteLine("it is true then!");

IfNull and IfNotNull

将List转换为数据表

public static class DataTableConverter
{
    /// <summary>
    /// Convert a List{T} to a DataTable.
    /// </summary>
    public static DataTable ToDataTable<T>(this IList<T> items)
    {
        var tb = new DataTable(typeof(T).Name);

        PropertyInfo[] props = typeof(T).GetProperties(BindingFlags.Public | BindingFlags.Instance);

        foreach (PropertyInfo prop in props)
        {
            Type t = GetCoreType(prop.PropertyType);
            tb.Columns.Add(prop.Name, t);
        }

        foreach (T item in items)
        {
            var values = new object[props.Length];

            for (int i = 0; i < props.Length; i++)
            {
                values[i] = props[i].GetValue(item, null);
            }

            tb.Rows.Add(values);
        }

        return tb;
    }

    /// <summary>
    /// Determine of specified type is nullable
    /// </summary>
    public static bool IsNullable(Type t)
    {
        return !t.IsValueType || (t.IsGenericType && t.GetGenericTypeDefinition() == typeof(Nullable<>));
    }

    /// <summary>
    /// Return underlying type if type is Nullable otherwise return the type
    /// </summary>
    public static Type GetCoreType(Type t)
    {
        if (t != null && IsNullable(t))
        {
            if (!t.IsValueType)
            {
                return t;
            }
            else
            {
                return Nullable.GetUnderlyingType(t);
            }
        }
        else
        {
            return t;
        }
    }
}

用法:

    IList<MyClass> myClassList = new List<MyClass>();
    DataTable myClassDataTable = myClassList.ToDataTable();