MSDN Magazine - December 2008 - (Page 32)

Graphical Elements Handlers of User Gestures Gateway to the Middle Tier View Controller Model Graphical Elements Handlers of User Gestures Gateway to the Middle Tier MVC Autonomous View Figure 3 From Autonomous View to MVC the controller. The model refers to the application data, manages the application’s functionalities, and notifies the view of state changes. The view is concerned with the content to display to users. Finally, the controller maps user gestures to actions on the model and updates the current view or selects the next view. These three actors are often referred to as the MVC triad. Figure 3 provides a graphical comparison between autonomous views and MVC applications. In MVC, the user interacts with the view, and actions (such as a button click) are captured by the view and forwarded to the controller. The controller decides what to do and does it through an interaction with the model. The model is essentially the business layer plus some extra capabilities. In particular, the model notifies the view about changes that may require an update of the UI. The model doesn’t know any details of the view, but between model and view there’s an “observer” relationship. In other words, the view holds a reference to the model and registers itself with the model to receive a notification of changes. When the notification is received, the view gets fresh data from the model and updates the UI. Figure 4 illustrates a sequence diagram of an MVC interaction. Note that in some MVC implementations, it’s the controller that notifies the view of the changes (see msdn.microsoft.com/ library/ms978748). MVC was devised to target desktop applications, but because of its relatively loose formulation, it was easily adapted for the Web. A popular Web variation of the MVC pattern is Model2. Model2 View Controller Model is the historical name of the pattern that fuels the ASP.NET MVC Framework today. User Gesture The Model2 pattern exposes the view to users through the browsInvoke Action er. User actions are captured by the browser and transformed into Execute the Requested Task a new HTTP request. In this way, requests flow from the browser to a special component (referred to as the front controller) sitting within the Web server. The front controller coordinates all of the Notify Changes requests that are made to the Web application. Ask for Changes In ASP.NET, the front controller takes the form of the URLrouting HTTP module. The HTTP module captures the request Updated Model and routes it to the appropriate controller for the requested action to take place. As the action method returns, the controller orders New View the view to refresh and passes fresh data for the new UI. The outto the User put of the view is captured by the front controller HTTP module and sent back to the browser. Figure 5 shows the sequence diagram for a typical Model2 interaction. You should note that the diagram includes only the genFigure 4 A Standard MVC Interaction eral steps. For example, in the ASP.NET MVC implementation of the pattern, the URL routBrowser URL Routing Controller Model View ing component does some work in addition to using the controller. Post A few differences exist between the original New MVC and Model2. As you can see, there’s no contact between the view and the model as in Invoke Action the MVC original formulation based on the Invoke Method aforementioned “observer” relationship. The user action is not captured and handled by Lookup View the view. The controller renders the view and explicitly passes display data to it. Render In ASP.NET, when you say MVC you should (viewData) HTML specify whether you mean Model2 or a manual implementation of MVC, as briefly explained in the beginning of this column. (If you’d like to read more on the ASP.NET MVC Framework, see msdn.microsoft.com/magazine/cc337884.) Figure 5 The Model2 Interaction as in the ASP.NET MVC Framework 32 msdn magazine Cutting Edge Model2: A Web Variation of MVC http://msdn.microsoft.com/library/ms978748 http://msdn.microsoft.com/library/ms978748 http://msdn.microsoft.com/magazine/cc337884

Table of Contents Feed for the Digital Edition of MSDN Magazine - December 2008

MSDN Magazine - December 2008 Contents Toolbox CLR Inside Out Advanced Basics Cutting Edge Patterns In Practice Team System Real-World WF Visual Studio OBA Tools SOA Data Access Geneva Framework Test Run Foundations Windows With C++ Going Places End Bracket

MSDN Magazine - December 2008

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