我觉得这个很有用:

public static class PaulaBean
{
    private static String paula = "Brillant";
    public static String GetPaula<T>(this T obj) {
        return paula;
    }
}

你可以在CodePlex上使用它。

我今天刚刚在博客上写了这个。它是INotifyPropertyChanged属性周围的强类型响应式包装器。

GetPropertyValues返回一个IObservable<T>的值，当它们改变时，从当前值开始。如果忽略当前值，可以对结果调用Skip(1)。

用法如下:

IObservable<int> values = viewModel.GetPropertyValues(x => x.IntProperty);

实现:

public static class NotifyPropertyChangeReactiveExtensions
{
    // Returns the values of property (an Expression) as they change, 
    // starting with the current value
    public static IObservable<TValue> GetPropertyValues<TSource, TValue>(
        this TSource source, Expression<Func<TSource, TValue>> property)
        where TSource : INotifyPropertyChanged
    {
        MemberExpression memberExpression = property.Body as MemberExpression;

        if (memberExpression == null)
        {
            throw new ArgumentException(
                "property must directly access a property of the source");
        }

        string propertyName = memberExpression.Member.Name;

        Func<TSource, TValue> accessor = property.Compile();

        return source.GetPropertyChangedEvents()
            .Where(x => x.EventArgs.PropertyName == propertyName)
            .Select(x => accessor(source))
            .StartWith(accessor(source));
    }

    // This is a wrapper around FromEvent(PropertyChanged)
    public static IObservable<IEvent<PropertyChangedEventArgs>>
        GetPropertyChangedEvents(this INotifyPropertyChanged source)
    {
        return Observable.FromEvent<PropertyChangedEventHandler, 
            PropertyChangedEventArgs>(
            h => new PropertyChangedEventHandler(h),
            h => source.PropertyChanged += h,
            h => source.PropertyChanged -= h);
    }
}

也许我写过和用过的最有用的扩展方法是:

http://www.codeproject.com/KB/cs/fun-with-cs-extensions.aspx?msg=2838918#xx2838918xx

这是一个扩展方法的ASP。Net MVC动作链接助手方法，该方法允许它使用控制器的授权属性来决定该链接是否应该从当前用户视图中启用、禁用或隐藏。 I使您不必在检查所有视图中的用户成员资格的“if”子句中包含受限制的操作。感谢Maarten Balliauw的想法和为我指明道路的代码位。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Security.Principal;
using System.Web.Routing;
using System.Web.Mvc;
using System.Collections;
using System.Reflection;
namespace System.Web.Mvc.Html
{
    public static class HtmlHelperExtensions
    {

        /// <summary>
        /// Shows or hides an action link based on the user's membership status
        /// and the controller's authorize attributes
        /// </summary>
        /// <param name="linkText">The link text.</param>
        /// <param name="action">The controller action name.</param>
        /// <param name="controller">The controller name.</param>
        /// <returns></returns>
        public static string SecurityTrimmedActionLink(
            this HtmlHelper htmlHelper,
            string linkText,
            string action,
            string controller)
        {
            return SecurityTrimmedActionLink(htmlHelper, linkText, action, controller, false, null);
        }

        /// <summary>
        /// Enables, disables or hides an action link based on the user's membership status
        /// and the controller's authorize attributes
        /// </summary>
        /// <param name="linkText">The link text.</param>
        /// <param name="action">The action name.</param>
        /// <param name="controller">The controller name.</param>
        /// <param name="showDisabled">if set to <c>true</c> [show link as disabled - 
        /// using a span tag instead of an anchor tag ].</param>
        /// <param name="disabledAttributeText">Use this to add attributes to the disabled
        /// span tag.</param>
        /// <returns></returns>
        public static string SecurityTrimmedActionLink(
            this HtmlHelper htmlHelper, 
            string linkText, 
            string action, 
            string controller, 
            bool showDisabled, 
            string disabledAttributeText)
        {
            if (IsAccessibleToUser(action, controller, HttpContext.Current ))
            {
                return htmlHelper.ActionLink(linkText, action, controller);
            }
            else
            {
                return showDisabled ? 
                    String.Format(
                        "<span{1}>{0}</span>", 
                        linkText, 
                        disabledAttributeText==null?"":" "+disabledAttributeText
                        ) : "";
            }
        }

        private static IController GetControllerInstance(string controllerName)
        {
            Assembly assembly = Assembly.GetExecutingAssembly();
            Type controllerType = GetControllerType(controllerName);
            return (IController)Activator.CreateInstance(controllerType);
        }

        private static ArrayList GetControllerAttributes(string controllerName, HttpContext context)
        {
            if (context.Cache[controllerName + "_ControllerAttributes"] == null)
            {
                var controller = GetControllerInstance(controllerName);

                context.Cache.Add(
                    controllerName + "_ControllerAttributes",
                    new ArrayList(controller.GetType().GetCustomAttributes(typeof(AuthorizeAttribute), true)),
                    null,
                    Caching.Cache.NoAbsoluteExpiration,
                    Caching.Cache.NoSlidingExpiration,
                    Caching.CacheItemPriority.Default,
                    null);

            }
            return (ArrayList)context.Cache[controllerName + "_ControllerAttributes"];

        }

        private static ArrayList GetMethodAttributes(string controllerName, string actionName, HttpContext context)
        {
            if (context.Cache[controllerName + "_" + actionName + "_ActionAttributes"] == null)
            {
                ArrayList actionAttrs = new ArrayList();
                var controller = GetControllerInstance(controllerName);
                MethodInfo[] methods = controller.GetType().GetMethods();

                foreach (MethodInfo method in methods)
                {
                    object[] attributes = method.GetCustomAttributes(typeof(ActionNameAttribute), true);

                    if ((attributes.Length == 0 && method.Name == actionName)
                        ||
                        (attributes.Length > 0 && ((ActionNameAttribute)attributes[0]).Name == actionName))
                    {
                        actionAttrs.AddRange(method.GetCustomAttributes(typeof(AuthorizeAttribute), true));
                    }
                }

                context.Cache.Add(
                    controllerName + "_" + actionName + "_ActionAttributes",
                    actionAttrs,
                    null,
                    Caching.Cache.NoAbsoluteExpiration,
                    Caching.Cache.NoSlidingExpiration,
                    Caching.CacheItemPriority.Default,
                    null);

            }

            return (ArrayList)context.Cache[controllerName + "_" + actionName+ "_ActionAttributes"]; 
        }

        public static bool IsAccessibleToUser(string actionToAuthorize, string controllerToAuthorize, HttpContext context)
        {
            IPrincipal principal = context.User;

            //cache the attribute list for both controller class and it's methods

            ArrayList controllerAttributes = GetControllerAttributes(controllerToAuthorize, context);

            ArrayList actionAttributes = GetMethodAttributes(controllerToAuthorize, actionToAuthorize, context);                        

            if (controllerAttributes.Count == 0 && actionAttributes.Count == 0)
                return true;

            string roles = "";
            string users = "";
            if (controllerAttributes.Count > 0)
            {
                AuthorizeAttribute attribute = controllerAttributes[0] as AuthorizeAttribute;
                roles += attribute.Roles;
                users += attribute.Users;
            }
            if (actionAttributes.Count > 0)
            {
                AuthorizeAttribute attribute = actionAttributes[0] as AuthorizeAttribute;
                roles += attribute.Roles;
                users += attribute.Users;
            }

            if (string.IsNullOrEmpty(roles) && string.IsNullOrEmpty(users) && principal.Identity.IsAuthenticated)
                return true;

            string[] roleArray = roles.Split(',');
            string[] usersArray = users.Split(',');
            foreach (string role in roleArray)
            {
                if (role == "*" || principal.IsInRole(role))
                    return true;
            }
            foreach (string user in usersArray)
            {
                if (user == "*" && (principal.Identity.Name == user))
                    return true;
            }
            return false;
        }

        private static Type GetControllerType(string controllerName)
        {
            Assembly assembly = Assembly.GetExecutingAssembly();
            foreach (Type type in assembly.GetTypes())
            {
                if (
                    type.BaseType!=null 
                    && type.BaseType.Name == "Controller" 
                    && (type.Name.ToUpper() == (controllerName.ToUpper() + "Controller".ToUpper())))
                {
                    return type;
                }
            }
            return null;
        }

    }
}

我在所有项目中用到的两个小技巧(有些人会觉得很傻)是:

public static bool IsNull(this object o){
  return o == null;
}

and

public static bool IsNullOrEmpty(this string s){
  return string.IsNullOrEmpty(s);
}

它使我的代码更流畅。

if (myClassInstance.IsNull()) //... do something

if (myString.IsNullOrEmpty()) //... do something

我认为这些是很好的扩展属性;如果我们能得到这些。

我喜欢这些NUnit Assert扩展:http://svn.caffeine-it.com/openrasta/trunk/src/Rasta.Testing/AssertExtensions.cs