What is ViewData in ASP .Net MVC C#?

ViewData is a dictionary-based container in ASP.NET MVC that enables data transfer from Controller to View. It stores key-value pairs where keys are strings and values are objects, making it a flexible but loosely-typed data transfer mechanism.

ViewData is valid only during the current HTTP request and provides one-way communication from controller to view. Since it uses string keys and object values, it requires explicit casting when retrieving data and does not provide compile-time type checking.

Syntax

Following is the syntax for storing data in ViewData −

ViewData["keyName"] = value;

Following is the syntax for retrieving data from ViewData −

Type variable = (Type)ViewData["keyName"];

Key Characteristics of ViewData

• Dictionary-based: Uses string keys to store and retrieve object values

• Loosely-typed: Requires explicit casting when retrieving data

• Request-scoped: Data is available only during the current HTTP request

• One-way transfer: Transfers data from Controller to View only

• No compile-time checking: Misspelled keys cause runtime errors, not compile-time errors

Using ViewData in Controller

Example

using System;
using System.Collections.Generic;
using System.Web.Mvc;

namespace DemoMvcApplication.Controllers {
    public class HomeController : Controller {
        public ViewResult Index() {
            ViewData["Countries"] = new List<string> {
                "India",
                "Malaysia", 
                "Dubai",
                "USA",
                "UK"
            };
            
            ViewData["Title"] = "Countries List";
            ViewData["Count"] = 5;
            
            return View();
        }
    }
}

Using ViewData in View

Example

@{
    ViewBag.Title = "Countries List";
}

<h2>@ViewData["Title"]</h2>
<p>Total Countries: @ViewData["Count"]</p>

<ul>
@foreach(string country in (List<string>)ViewData["Countries"]) {
    <li>@country</li>
}
</ul>

Output

Countries List
Total Countries: 5

? India
? Malaysia  
? Dubai
? USA
? UK

ViewData vs ViewBag vs TempData

Common Use Cases

• Passing simple data: Strings, numbers, or basic objects to views

• Page metadata: Titles, descriptions, or configuration values

• Collection data: Lists or arrays for dropdown menus or tables

• Conditional rendering: Flags to control view behavior

Conclusion

ViewData provides a simple dictionary-based mechanism for passing data from Controller to View in ASP.NET MVC. While it offers flexibility, it lacks compile-time type checking and requires explicit casting, making ViewBag or strongly-typed models often preferable for complex scenarios.