原文URL：http://www.asp.net/learn/mvc/tutorial-03-cs.aspx

Understanding Controllers

1. Controller定义
  MVC controllers are responsible for responding to requests made against an ASP.NET MVC website. Each browser request is mapped to a particular controller. For example, imagine that you enter the following URL into the address bar of your browser:

http://localhost/Product/Index/3

In this case, a controller named ProductController is invoked. The ProductController is responsible for generating the response to the browser request. For example, the controller might return a particular view back to the browser or the controller might redirect the user to another controller.

A controller is a class that derives from the base System.Web.Mvc.Controller class.

Understanding Controller Actions

1. Action定义
  An action is a method on a controller that gets called when you enter a particular URL in your browser address bar. For example, imagine that you make a request for the following URL:

http://localhost/Product/Index/3

In this case, the Index() method is called on the ProductController class. The Index() method is an example of a controller action.

2. Action的使用注意事项
  2.1 A controller action must be a public method of a controller class.
  2.2 A method used as a controller action cannot be overloaded.
  2.3 A controller action cannot be a static method.

Understanding Action Results

1. Action Result定义
  A controller action returns something called an action result. An action result is what a controller action returns in response to a browser request.

2. Action Results类型
  The ASP.NET MVC framework supports several types of action results including:

1.ViewResult – Represents HTML and markup.
  2.EmptyResult – Represents no result.
  3.RedirectResult – Represents a redirection to a new URL.
  4.JsonResult – Represents a JavaScript Object Notation result that can be used in an AJAX application.
  5.JavaScriptResult – Represents a JavaScript script.
  6.ContentResult – Represents a text result.
  7.FileContentResult – Represents a downloadable file (with the binary content).
  8.FilePathResult – Represents a downloadable file (with a path).
  9.FileStreamResult – Represents a downloadable file (with a file stream).

All of these action results inherit from the base ActionResult class.

2. Action Results类型使用说明

In most cases, a controller action returns a ViewResult.

Normally, you do not return an action result directly. Instead, you call one of the following methods of the Controller base class:

1.View – Returns a ViewResult action result.
  2.Redirect – Returns a RedirectResult action result.
  3.RedirectToAction – Returns a RedirectToRouteResult action result.
  4.RedirectToRoute – Returns a RedirectToRouteResult action result.
  5.Json – Returns a JsonResult action result.
  6.JavaScriptResult – Returns a JavaScriptResult.
  7.Content – Returns a ContentResult action result.
  8.File – Returns a FileContentResult, FilePathResult, or FileStreamResult depending on the parameters passed to the method.

So, if you want to return a View to the browser, you call the View() method. If you want to redirect the user from one controller action to another, you call the RedirectToAction() method.

The ContentResult action result is special. You can use the ContentResult action result to return an action result as plain text.

If a controller action returns a result that is not an action result – for example, a date or an integer – then the result is wrapped in a ContentResult automatically.