Working with Controllers and Actions in MVC

Working with
Controllers and Actions
in MVC

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Copyright © by Application Developers Training Company

Objectives
• Learn how controllers manage MVC applications
• Understand action methods and how they can
receive input
• Explore how you can return a result from an
action method


Agenda
• Introduction to Controllers
• Using a Controller to Manage the Application
• Controller Actions
• Returning Action Results


Introduction to Controllers


• Controller is the traffic cop to keep things smooth


 Responds to user input


 Manages overall flow of application


 Interacts with model to change state and data


 Selects a result to respond to user


• Does not itself contain UI, data, or business logic
code


code
• Ultimately responsible for servicing requests


code
 The application’s logic


code
 The application’s logic
• Lots of attention in MVC 3


Using a Controller to Manage the
Application


Application
• Powerful but easy to use


Application
• Implemented as .NET class with properties and
methods


Application
methods
• System.Web.Mvc namespace


Application
methods
 Your controllers are likely to need very little code


Application
methods
 Your controllers are likely to need very little code
 Routine infrastructure encapsulated in base classes


Controllers in System.Web.Mvc


• Controller must:


 Implement IController interface


 Have a name ending in “Controller”


 Marked public, not abstract, no generic parameters


• Otherwise, not recognized as controller


 Methods never called as action methods


• Normally inherit from Controller class


 Which inherits from ControllerBase


 Which inherits from ControllerBase
 Which implements IController


The IController Interface


• IController requirement isn’t onerous


• Single purpose: find a controller and call Execute
method


method
• Simple interface definition:


method
public interface IController {
void Execute(RequestContext requestContext);
}


method
public interface IController {
void Execute(RequestContext requestContext);
}

• When request arrives
 Routing identifies controller, calls Execute
 Passes in object with context information


The ControllerBase Abstract Base
Class


Class
• Implements IController


Class
 Adds controller features, such as TempData and
ViewData


Class
ViewData
 Execute method creates ControllerContext object


Class
ViewData
• Still pretty lightweight


Class
ViewData
 Relatively little added functionality


Class
ViewData
 Relatively little added functionality
 Could build Web site with either IController or
ControllerBase


The Controller Class


• Rich implementation of controller infrastructure


• Inherits from ControllerBase


 So indirectly implements IController


• Added features include


 Action methods


 Action methods
 Action results


 Action methods
 Action results
 Filters


 Action methods
 Action results
 Filters
• Normally should implement your controllers
using Controller


The MVC Request Processing


• Response process to every user request


 IIS, ASP.NET, MVC collaboration



Request



Request
HTTP



Request
HTTP

Routing Engine Controller Factory Controller

View Action Method Action Invoker



Request
HTTP



HTTP



Request
HTTP



Response
HTTP


Action Method Selection


• Job of the action invoker


• More complicated than initially appears


 Multiple overloaded methods with same name


 Decorated with attributes that control use


 Action name may be different from method name


• Starts by getting action portion of route
{controller}/{action}/{id}


 Default action is “Index”


• Then map action name to controller method


• Then map action name to controller method
 Simplest: one method with that action name

Action Method Qualifications


• Method must meet requirements to be action
method:


method:
 Public and not static or Shared


method:
 Cannot be defined on System.Object or Controller


method:
o i.e., ToString() could not be an action method


method:
 Cannot be a special method


method:
 Cannot have a NonAction attribute


method:
• Action invoker uses reflection to find candidates


method:
 All methods with same action name


method:
 All methods with same action name
 But method attributes can make this murky with
multiple candidates

ActionName Attribute


• Normal convention is for controller method name
to be same as action name


• Can give it a different action name


 Action name that is not a legal language name


 Use an MVC component name as action name


 Use an MVC component name as action name
 Different naming standards


ActionMethodSelector Attribute


• Now action invoker has list of all matching action
names


names
• Next examines ActionMethodSelector attributes


names
 Control what conditions a method should be used for a
request


names
request
 Single method: IsValidForRequest


names
request
o Executes on each candidate action method


names
request
o Return false, removed from list


names
request

• Implementations


names
request

• Implementations
 NonAction attribute


names
request

• Implementations
 AcceptVerbs attribute


names
request

• Implementations
 AcceptVerbs attribute
 HttpDelete, HttpGet, HttpPost, HttpPut

Controller Actions


Controller Actions
• Once invoked, action method does its job


Controller Actions
 Receive and process input


Controller Actions
 Perform processing


Controller Actions
 Generate output


Controller Actions
 Generate output
o Select a view


Controller Actions
 Generate output
o Select a view
o Write output directly to page


Controller Actions
 Generate output
o Select a view
o Raw data to browser


Controller Actions
 Generate output
o Select a view
o Raw data to browser
o Do nothing


Action Method Input


Action Method Input
• Most methods need data to do work


Action Method Input
• Can come from a variety of sources


Action Method Input
 Environment


Action Method Input
 Environment
 Operating system


Action Method Input
 Environment
 Nature of user request


Action Method Input
 Environment
 Direct parameters


Action Method Input
 Environment
 Many others


Action Method Input
 Environment
 Many others
• Three broad sources for action method


Action Method Input
 Environment
 Many others
 Context objects


Action Method Input
 Environment
 Many others
 Context objects
 Method parameters


Action Method Input
 Environment
 Many others
 Context objects
 Method parameters
 Model bindings

Context Object Input


• Web requests come loaded with information


 HTTP headers


 HTTP headers
 User information


 HTTP headers
 Browser and capability information


 HTTP headers
 User’s IP address


 HTTP headers
 Authentication information


 HTTP headers
 Authentication information
• Information available through context objects


Parameter Input


Parameter Input
• Specialized input customized for method


Parameter Input
• MVC takes care of populating values


Parameter Input
• Action invoker examines context objects for
parameter values and uses model binder


Parameter Input
1. Request.Form


Parameter Input
1. Request.Form
2. RouteData.Values


Parameter Input
1. Request.Form
2. RouteData.Values
3. Request.QueryString


Parameter Input
1. Request.Form
2. RouteData.Values
• Matches solely by name in order


Parameter Input
1. Request.Form
2. RouteData.Values
 Once it finds a match it stops searching


Parameter Input
1. Request.Form
2. RouteData.Values
 Once it finds a match it stops searching
 Have to coordinate names to avoid duplicate names

Model Bindings


Model Bindings
• Model encapsulates data and business rules


Model Bindings
 Use directly in controllers and views


Model Bindings
 Built-in features to make easy


Model Bindings
 Built-in features to make easy
 Automatic data scaffolding


Controller Session State


• SessionState attribute


 Control how and whether controller uses session state


 MVC uses session state by default, if available


• SessionStateBehavior enumeration


 Default


 Default
 Disabled


 Default
 Disabled
 ReadOnly


 Default
 Disabled
 ReadOnly
 Required


Returning Action Results


• Action method follows a normal process


 Receives request and data


 Process the request


 Generates response


• Many possible responses


• Three broad types of results


 HTML


 HTML
 Redirect somewhere else


 HTML
 Page data


 HTML
 Page data
• All options based on ActionResult

Action Result


Action Result
• ActionResult base class


Action Result
public abstract class ActionResult {
public abstract void ExecuteResult(ControllerContext context);
}


Action Result
public abstract class ActionResult {
public abstract void ExecuteResult(ControllerContext context);
}

• ExecuteResult receives context information
• Takes care of low-level work of generating a
response


ActionResult Types


ActionResult Types
Type Helper Method Description
ContentResult Content() Raw text data
EmptyResult -- Returns nothing
FileResult File() Base class to send file
HttpNotFoundResult HttpNotFound() Returns HTTP 404
HttpStatusCodeResult -- Returns any HTTP status
HttpUnauthorizedResult -- Returns HTTP 401
JavaScriptResult JavaScript() Returns and executes script
JsonResult Json() JavaScript Object Notation
PartialViewResult PartialView() HTML snippet
RedirectResult Redirect() Redirect to URL
RedirectToRouteResult RedirectToRoute() Redirect to MVC route or action
ViewResult RedirectToAction()
View() Full HTML page

Passing Data to the View


• Use either ViewData or ViewBag


 Different faces of the same feature


 A bit like ASP.NET Session object


 Exposes ViewDataDictionary


 But ViewData/ViewBag disappear after view rendered


 Session lasts for the user session


• ViewData is loosely typed


• ViewBag is strongly typed


• ViewBag is strongly typed
 Uses dynamic language feature of C# and VB


ViewData and ViewBag


• Not limited to passing strings


• Keep in mind that they are same feature, but
different


different
 Can mix and match in one action method/view


different
 Get the same result either way


different
 Generally should use ViewBag


different
 Generally should use ViewBag
• But in VB, using in controller requires setting
Option Strict Off


Returning Text Data: ContentResult


• HTML is dominant data format


 But browsers can deal with variety of formats


• Use a ContentResult for other formats


 Content helper method


 Specify content as string


 Specify content as string
 Optionally specify type, such as text/xml


Implicit Action Results


• Return text and don’t need to specify type


• If type is not string, calls ToString method with
InvariantCulture setting


• If type is not string, calls ToString method with
InvariantCulture setting
 Wraps in ContentResult object


Missing Resource:


Missing Resource:
• Useful to indicate that requested resource is not
available


Missing Resource:
available
 User hacks a URL


Missing Resource:
available
• Returns HTTP 404 status code


Missing Resource:
available
• Returns HTTP 404 status code
 Can mask an exception that an attacker could
otherwise use


Return any HTTP Status Code:


• More flexible than HttpNotFoundResult


• Can specify any HTTP status code


• Can specify any HTTP status code
 Optional description


Redirection Methods


Redirection Methods
• Methods on the Controller class


Redirection Methods
• Return instances of redirection action methods


Redirection Methods
 Permanent property set to true


Redirection Methods
• Types


Redirection Methods
• Types
 RedirectPermanent method


Redirection Methods
• Types
 RedirectToRoutePermanent method


Redirection Methods
• Types
 RedirectToActionPermanent method


Redirection Methods
• Types
• Make easy to manage permanent redirections


Redirection Methods
• Types
• Make easy to manage permanent redirections
 HTTP 301 status code


Learn More!


Learn More!
• This is an excerpt from a larger course. Visit
www.learnnowonline.com for the full details!


Working with Controllers and Actions in MVC

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