ViewBag, ViewData, TempData, Session, and Strongly Typed Models

In ASP.NET Core MVC applications, efficiently passing data from controllers to views is crucial for dynamic and responsive web development. This article explores five powerful techniques for data passing: ViewBag, ViewData, TempData, Session, and Strongly Typed Models. We’ll delve into the purpose, usage, benefits, and limitations of each method, offering practical examples to illustrate their application. Whether you’re a seasoned developer or new to ASP.NET Core, this guide will equip you with the knowledge to choose the right approach for your specific needs, ensuring seamless data handling in your projects.

In ASP.NET Core MVC applications, there are several ways to pass data from a controller to a view. Each method has its own use cases, benefits, and limitations. Let's break down each one:

1. ViewBag

• Purpose: Pass data from the controller to the view.

• Syntax: Uses dynamic properties.

• Example:

  // Controller
  public IActionResult Index() {
      ViewBag.Message = "Hello, ViewBag!";
      return View();
  }
  
  // View (Index.cshtml)
  <h2>@ViewBag.Message</h2>

• Advantages: Easy to use with a dynamic syntax.

• Disadvantages: Not type-safe, can lead to runtime errors if mistyped.

2. ViewData

• Purpose: Pass data from the controller to the view.

• Syntax: Uses a dictionary-like structure.

• Example:

  // Controller
  public IActionResult Index() {
      ViewData["Message"] = "Hello, ViewData!";
      return View();
  }
  
  // View (Index.cshtml)
  <h2>@ViewData["Message"]</h2>

• Advantages: Allows passing data using key-value pairs.

• Disadvantages: Not type-safe, requires casting.

3. TempData

• Purpose: Pass data between actions, especially useful for redirects.

• Syntax: Uses a dictionary-like structure.

• Example:

  // Controller - Action1
  public IActionResult Action1() {
      TempData["Message"] = "This is TempData!";
      return RedirectToAction("Action2");
  }
  
  // Controller - Action2
  public IActionResult Action2() {
      var message = TempData["Message"];
      return View();
  }
  
  // View (Action2.cshtml)
  <h2>@TempData["Message"]</h2>

• Advantages: Data persists for a single subsequent request.

• Disadvantages: Data is automatically removed after it is accessed.

4. Session

• Purpose: Store user-specific data across multiple requests.

• Syntax: Uses the session API.

• Example:

  // Controller - Set Session
  public IActionResult SetSession() {
      HttpContext.Session.SetString("Message", "Hello, Session!");
      return View();
  }
  
  // Controller - Get Session
  public IActionResult GetSession() {
      var message = HttpContext.Session.GetString("Message");
      return View(model: message);
  }
  
  // View (GetSession.cshtml)
  <h2>@Model</h2>

• Advantages: Data persists for the duration of the user's session.

• Disadvantages: Can consume server memory, requires server configuration.

5. Strongly Typed Models

• Purpose: Pass data using models to ensure type safety and structure.

• Syntax: Uses model classes.

• Example:

  // Model
  public class MyViewModel {
      public string Message { get; set; }
  }
  
  // Controller
  public IActionResult Index() {
      var model = new MyViewModel { Message = "Hello, Strongly Typed Model!" };
      return View(model);
  }
  
  // View (Index.cshtml)
  @model MyViewModel
  <h2>@Model.Message</h2>

• Advantages: Type-safe, easy to validate, structured data.

• Disadvantages: Requires more setup and maintenance.

Comparison Summary

Method	Type-Safety	Persistence Scope	Use Case
ViewBag	No	Current request	Simple data passing from controller to view.
ViewData	No	Current request	Simple data passing from controller to view.
TempData	No	Single subsequent request	Data across redirects.
Session	No	User's session duration	User-specific data across requests.
Strongly Typed Models	Yes	Current request	Structured, type-safe data passing.