ASP.NET MVC: Transferring Data and Action Results

• Transferring data from controllers involves using ViewBag and ViewData properties.
• Using a view model transfers data from a controller to a strongly-typed view.
• TempData property enables web apps to redirect and transfer data from one controller to another.
• Important interfaces and classes form the ActionResult hierarchy.
• One needs to distinguish between the ViewBag and ViewData properties.
• A view model transfers data from a controller to a view.
• Action methods can redirect to other action methods.
• The PRG pattern prevents resubmission of POST data.
• Distinctions exist between the ViewData and TempData properties.
• The Keep() and Peek() methods serve specific purposes within the TempData class.

ActionResult Hierarchy

• The hierarchy includes IActionResult(interface).
• It also includes ActionResult(abstract), and ViewResult.
• RedirectResult, JsonResult, and FileResult are also part of the hierarchy.

Common ActionResult Subtypes

• Common subtypes include ViewResult, RedirectResult, and RedirectToActionResult.
• JsonResult, FileResult, and StatusCodeResult are also common.
• ContentResult and EmptyResult also fall under common subtypes.
• More ActionResult subtypes are available at: https://docs.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.mvc.actionresult

Controller Class Methods (ActionResult)

• The Controller class has methods that return an ActionResult object, like View(), Redirect(), and RedirectToAction().
• File() and Json() are also methods that return an ActionResult object.

Overloads of the View() method

• Overloads include View(), View(model), View(name), and View(name, model).

ViewResult Object Example

• To return a ViewResult object, follow this exampple: public ViewResult List() {var names = new List<string> { "Grace", "Ada", "Charles" };return VIew(names);}

RedirectToActionResult Example

• An action method to return a RedirectToActionResult object: public RedirectToActionResult Index() => RedirectToAction("List");

Action Method with Different Result Types

• Example of an action method returning different result object types : [HttpPost] public IActionResult Edit(string id) { if (ModelState.IsValid) {return RedirectToAction("List");} return View((object)id);}

ViewData Property

• Adding items to the ViewData property in controller code: public ViewResult Index() { ViewData["Book"] = "Alice in Wonderland"; ViewData["Price"] = 9.99; return View();}

ViewDataDictionary Class Properties

• Includes Count, Keys, and Values.

Razor Code to Show ViewData Items

• Sample Razor code displays all items in the ViewData object: <h2>@ViewData.Count items in ViewData</h2> @foreach (KeyValuePair<string, object?> item in ViewData) { <div>@item.Key - @item.Value</div> }
• Output is 2 items in ViewData, "Book - Alice in Wonderland", and "Price - 9.99".

Casting a ViewData Object

• Razor code casts a ViewData object to a double type: <h4>Price: @(((double)ViewData["Price"]).ToString("c"))</h4>
• Results in "Price: $9.99" in browser.

Checking ViewData for Null

• Razor code checks ViewData for null: <h4>Price: @(((double?)ViewData["Price"])?.ToString("c"))</h4>
• It casts a value type (double) to a nullable type.
• It also casts a reference type (string) to a nullable type using: <h4>Book: @ViewData["Book"]?.ToString().ToUpper()</h4>

ViewBag Property Example

• Controller code adding dynamic properties to the ViewBag: public ViewResult Index() { ViewBag.Book = "Alice in Wonderland"; ViewBag.Price = 9.99; return View();}

Razor Code to show ViewBag Properties

• Razor code displays ViewBag properties using ViewData: <h2>@ViewData.Count ViewBag properties</h2> @foreach (KeyValuePair<string, object?> item in ViewData) { <div>@item.Key - @item.Value</div> }
• The browser shows "2 ViewBag properties" with "Book - Alice in Wonderland" and "Price - 9.99".

Working with ViewBag (No Casting)

• Razor code works with a ViewBag property without casting: <h4>Price: @ViewBag.Price.ToString("c")</h4>
• The view displays "Price: $9.99".

Checking ViewBag Properties for Null

• Razor code example: <h4>Price: @ViewBag.Price?.ToString("c")</h4>
• Used for a value type (double).
• Razor code example: <h4>Book: @ViewBag.Book?.ToUpper()</h4>
• Used for a reference type (string).
• The Key name must be valid to be used in C#.
• Can call properties and methods of the ViewDataDictionary class.
• You can loop through all the items in the ViewData dictionary.

NFL Team Organization

• The teams of the National Football League (NFL) are organized in two conferences: NFC and AFC.
• Four divisions exist within each conference: North, South, East, and West.
• Four teams per division.

Conference Class Definition

• Defines the structure for conference data with properties for ConferenceID and Name.

Division Class Definition

• Includes properties for DivisionID and Name.

Team Class Definition

• Contains properties for TeamID, Name, Conference, Division, and LogoImage.

TeamContext Class

• Sets up the database context, including seeding initial data like conference and division names.

Home Controller Details

• HomeController class manages the interactions and data retrieval for the NFL Teams app.
• Methods store selected conference and division IDs in the view bag, and retrieves conference and division data from the database.
• Filters teams by conference and division, passes the list of teams to view as a model.

Custom Route

• The custom route in Program.cs defines a specific route pattern for conference and division display.
• A default route is also present.

Layout

• The layout includes meta, links to bootstrap and site css.
• It loads in the ViewBag title.

Home/Index View:

• It displays team data based on the model passed from the controller.
• Loops through conferences and divisions to create links.
• Loops through teams to display their logos and names.

TeamsViewModel class

• A view model provides a structured way to pass data to the view.
• A view model is used including lists of teams, conferences, and divisions, along with methods to determine active links.

Updated Home Controller

• Populates the model with the lists of teams, conferences, and divisions.

Updated Home/Index View

• Loops to generate appropriate HTML elements for dynamic content display.

HTTP Status Codes (Redirection)

• 302 Found, and 301 Moved Permanently are used for redirection.

ActionResult Subtypes (Redirection)

• Includes RedirectResult, LocalRedirectResult, RedirectToActionResul, RedirectToRouteResult.
• Redirect() is a 302 Found method, RedirectPermanent() is a 301 Moved Permanently method.
• LocalRedirect() is a 302 Found method, LocalRedirectPermanent() is a 301 Moved Permanently method.
• RedirectToAction() is a 302 Found method, RedirectToActionPermanent() is a 301 Moved Permanently method.
• RedirectToRoute() is a 302 Found method, RedirectToRoutePermanent() is a 301 Moved Permanently method.

Subtype Usage (Redirection)

• RedirectResult is used to redirect to an external URL.
• LocalRedirectResult ensures redirection happens within the app.
• RedirectToActionResult redirects to an action method within the app.
• RedirectToRouteResult redirects using a named route within the app.

RedirectToAction() Overloads

• (a): Redirects to the specified action in current controller.
• (a, c): Redirects to the specified action in specified controller.
• (a, routes): Redirects to the specified action in the current controller using route parameters.
• (a, c, routes): Redirects to the specified action in the specified controller using route parameters.

Redirecting Action Methods

• In the current controller: public RedirectToActionResult Index() => RedirectToAction("List");
• In the Team controller: public RedirectToActionResult Index() => RedirectToAction("List", "Team");
• With a parameter in current controller: public RedirectToActionResult Index(string id) => RedirectToAction("Details", new { ID = id });
• Use shortcut for variable and route segment name match: public RedirectToActionResult Index(string id) => RedirectToAction("Details", new { id });
• To supply parameters with a string-string dictionary: public RedirectToActionResult Index(string id) => RedirectToAction("Details", new Dictionary<string, string>(){ { "ID", id } });

Browser Message (POST Request)

• Browsers display a confirmation message when refreshing a page displayed by a POST request
• The purpose is to prevent resubmission.