扩展方法:

public static void AddRange<T, S>(this ICollection<T> list, params S[] values)
    where S : T
{
    foreach (S value in values)
        list.Add(value);
}

该方法适用于所有类型，并允许您将一系列项作为参数添加到列表中。

例子:

var list = new List<Int32>();
list.AddRange(5, 4, 8, 4, 2);

我喜欢下面这些方法来处理带有Flags属性集的枚举:

public static bool AnyOf(this object mask, object flags)
{
    return ((int)mask & (int)flags) != 0;
}
public static bool AllOf(this object mask, object flags)
{
    return ((int)mask & (int)flags) == (int)flags;
}
public static object SetOn(this object mask, object flags)
{
    return (int)mask | (int)flags;
}
etc.

使用示例:

var options = SomeOptions.OptionA;
options = options.SetOn(OptionB);
options = options.SetOn(OptionC);

if (options.AnyOf(SomeOptions.OptionA | SomeOptions.OptionB))
{
etc.

原始方法来自本文:http://www.codeproject.com/KB/cs/masksandflags.aspx?display=Print 我只是把它们转换成扩展方法。

但它们的一个问题是对象类型的参数，这意味着所有对象最终都被这些方法扩展，而理想情况下，它们应该只应用于枚举。

更新 根据评论，你可以绕过“签名污染”，以牺牲性能为代价，如下所示:

public static bool AnyOf(this Enum mask, object flags)
{
    return (Convert.ToInt642(mask) & (int)flags) != 0;
}

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>();

与时间跨度相关的扩展，如:

public static TimeSpan Seconds(this int seconds)
{
  return TimeSpan.FromSeconds(seconds);
}

public static TimeSpan Minutes(this int minutes)
{
  return TimeSpan.FromMinutes(minutes);
}

允许使用:

1.Seconds()
20.Minutes()

像这样的锁定扩展:

public static IDisposable GetReadLock(this ReaderWriterLockSlim slimLock)
{
  slimLock.EnterReadLock();
  return new DisposableAction(slimLock.ExitReadLock);
}

public static IDisposable GetWriteLock(this ReaderWriterLockSlim slimLock)
{
  slimLock.EnterWriteLock();
  return new DisposableAction(slimLock.ExitWriteLock);
}

public static IDisposable GetUpgradeableReadLock(this ReaderWriterLockSlim slimLock)
{
  slimLock.EnterUpgradeableReadLock();
  return new DisposableAction(slimLock.ExitUpgradeableReadLock);
}

允许使用像这样的锁:

using (lock.GetUpgradeableReadLock())
{
  // try read
  using (lock.GetWriteLock())
  {
    //do write
  }
}

还有许多来自Lokad共享图书馆的其他书籍

在这里找到更多的例子:www.extensionmethod.net

日期时间扩展

例子:

DateTime firstDayOfMonth = DateTime.Now.First();
DateTime lastdayOfMonth = DateTime.Now.Last();
DateTime lastFridayInMonth = DateTime.Now.Last(DayOfWeek.Friday);
DateTime nextFriday = DateTime.Now.Next(DayOfWeek.Friday);
DateTime lunchTime = DateTime.Now.SetTime(11, 30);
DateTime noonOnFriday = DateTime.Now.Next(DayOfWeek.Friday).Noon();
DateTime secondMondayOfMonth = DateTime.Now.First(DayOfWeek.Monday).Next(DayOfWeek.Monday).Midnight();