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The MVC pattern splits an application into three layers: the model, the view, and the controller.
The model represents core business logic and data. Models encapsulate the properties and behavior of a domain entity and expose properties that describe the entity.Controllers typically instantiate the model in its actions and then provide the model to the view for display.
In general, you can build your model, domain, view, or input modeling in different ways. You use a domain model when the object you are using describes the data you work with in the middle tier of that application. If you are using Entity Framework, for example, and present these objects to a view for display, you are using a domain model approach for creating your model.
A view model approach describes the data being worked on in the presentation layer. Any data you present in the view is found within the properties of the view model class, which represents all the data the controller transmits to the view after processing the request. A view model is generally the result of aggregating multiple classes into a single object.
The input model faithfully represents the data being uploaded to the server from the client with each individual HTTP request. The input model approach uses model binding to capture user input. When you consider a typical complex data entry form, you might have one entry form that captures information that would typically span across multiple objects in a domain, such as name, address, employers, phone numbers, and other values. Those objects would get mapped to different domain objects. The use of an input model, however, enables all the work to create and manage these domain objects to stay within a single controller and model.
Model binders are a simple way to map posted form data to a type and pass that type to an action method as a parameter. The DefaultModelBinder automatically maps input values to model properties if the names match precisely. The model binder implements the IModelBinder interface and contains a GetValue method that retrieves the value of a specified parameter or type. You can use existing value providers to evaluate request values or you can create custom value providers for special evaluation.
Model binding is recursive and transverses complex object graphs. ASP.NET MVC enables you to create custom model binders, which is useful because the default model binder does not support abstract classes or interfaces. There are times when that ability is necessary, especially if you want to use dependency injection and inversion of control
The view is the part of the application responsible for displaying information to users.The controller gives the view a reference to the model or the information that needs to be displayed.
The following are additional considerations when working with a view:
■Strongly-typed views: Eliminates the need for casting in the view by setting the attached model property. The view engine can work with the information through mapped class values rather than through a string-based lookup.
■View-specific model: An intermediate class for when the display does not map directly to a domain object. The view-specific model gathers all the values that are needed for the view from one or more model objects into a single class specifically designed for that view.
■ Partial view :ASP.NET MVCs version of a user control that can be displayed within a page. The Razor view engine displays it the same as a full view, but without including the <html> and <head> tags.
■ Master or layout page: A way to share a design across multiple pages. This page is a building block for the application because it contains much of the wrapper HTML code that turns your output into a format understood by web browsers.
■ Scaffold template:A template that creates standard pages as part of the process when creating a project. This ability gives you a quick start on development. Because the default scaffold types are Visual Studio T4 templates, you can alter the existing scaffold types or create a new one.
RAZOR VIEW AND WEB FORMS VIEW ENGINES:
The Razor view provides a streamlined, compact, expressive, and fluid format that minimizes the amount of coding required within a view. Razor also supports the concept of layouts, which help maintain a consistent look and feel across multiple views within an application.
The Web Forms view engine was the initial view engine. It is similar to ASP.NET and provides a familiar experience to an ASP.NET developer. The Razor view engine uses the @ code delimiter; Web Forms uses the <% notation.
string title = article.Title.ToUpper();
string title = article.Title.ToUpper();
Controllers are the part of ASP.NET MVC 4 that handles incoming requests, handles user input and interaction, and executes application logic. A controller calls the model to get the required business objects, if any, and then calls the view, either with or without a model, to create and render the output HTML. A controller is based on the ControllerBase class and is responsible for locating the appropriate action method to call, getting values in the model to use as parameters, managing all errors, and calling the view engine to write the page. It is the primary handler of the interaction from the user.Action methods are typically one-to-one mappings to user interactions. Each user interaction creates and calls a uniform resource locator (URL). The routing engine parses the URL using routing rules to determine the controller and action method that needs to be called.Because action methods map to user interactions, an action method is called every time a user does something that interacts with the server.
A better approach when laying out the controller structure is to have a controller for each type of object with which the user will be interacting on the screen. This enables you to compartmentalize the functionality around the object into a single place, making code management simpler and providing more easily understandable URLs.
Actions and Action Results:
Routes and Routing:
The routing table is stored in the Global.asax file. The routing system enables you to define URL mapping routes and then handle the mapping to the right controller and actions. It also helps construct outgoing URLs used to call back to the controller/actions.
The routing engine its only job is to analyze URLs and pass control to the route handler. The route handler is there to find an HTTP handler, or an object implementing the IHttpHandler interface, for a request. MvcHandler, the default handler , extracts the controller information by comparing the request with the template values in the routing table. The handler extracts the string and sends it to a controller factory that returns the appropriate controller. The controller factory is easily extendable by creating a custom controller factory that implements IControllerFactory.
Controller actions have attributes that provide additional information to the framework. The most-used select attributes are ActionName, AcceptVerbs, and NonAction, which help the framework determine which action to run. Filter attributes enable you to add caching, validation, and error handling through the use of OutputCache, ValidateInput, and HandleError. Because the attributes are part of ASP.NET MVC, they are customizable as well. You can create custom action filters that surround an action with custom logic by overriding the base ActionFilter class.
Asynchronous action methods are useful for long-running, non-CPU-bound requests because they avoid blocking the web server from performing work while the method request is still pending. When designing your action methods, you need to determine whether to use synchronous or asynchronous processing. You should strongly consider asynchronous methods when the operation is network-bound or I/O-bound rather than CPU-bound. Also, asynchronous methods make sense when you want to enable the user to cancel a longrunning method.
The key to using the new asynchronous framework is the Task framework in the System.Threading.Tasks namespace. The purpose of Task is to provide a pluggable architecture to increase flexibility and to make multitasking applications easier to write. To create an asynchronous action on a controller, mark the controller as async and change the return from an ActionResult into a Task<ActionResult>.
This kind of approach makes sense if you are merging the results from multiple service calls into a single model to be passed to the view. Another approach is to use an asynchronous partial view. This helps the overall performance of your application by running the work in that partial view in a different thread, enabling the primary thread to continue to process other items.
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