What is ViewData and ViewBag?

In ASP.NET MVC, ViewData and ViewBag are used to pass data between a controller and a view. While they serve the same purpose, there are some differences in their implementation and usage.


ViewData is a dictionary of objects that is derived from the ViewDataDictionary class. It allows you to store and retrieve data using string keys. It is accessible within both the controller and the corresponding view. The data stored in ViewData is available only for the duration of the current request. If you set data in the controller action and use it in the view, it will be available during that request and will not persist across subsequent requests. ViewData requires type casting for complex data types and null value checks to avoid errors.


On the other hand, ViewBag is a dynamic property introduced in C# 4.0. It is a convenient way to pass data between a controller and a view without requiring explicit type casting. Internally, ViewBag properties are stored as name/value pairs in the ViewData dictionary. Like ViewData, ViewBag data is also valid only for the duration of the current request. However, ViewBag simplifies the process of accessing data by eliminating the need for type casting. It allows you to access the properties directly in the view using dynamic syntax.


Both ViewData and ViewBag serve the purpose of passing data from the controller to the view, but ViewBag provides a more concise and dynamic way of accessing the data in the view. It is important to note that neither ViewData nor ViewBag should be used for complex data sharing or for storing data that needs to persist beyond the current request. In such cases, it is recommended to use other mechanisms like model binding, session state, or TempData.