NET3.5中的扩展方法，DEMO直接通过IEnumerable<T>来自定义调用过滤方法

namespace ConsoleApplication2
{
public static class Filter
{
public static IEnumerable ForUser(this IEnumerable qry, string userName)
{
return from a in qry
where
a.Contains(userName.ToLower())
select a;
}

///

/// 自定义起用调用static方法过滤
///

public static void CustExample()
{
IEnumerable x = new List { "1", "zzq", "good" }; //为对象赋值
foreach (var item in x.ForUser("zzq"))
{
Console.WriteLine(item);
}
}