How do you store and retrieve data in session state?

In ASP.NET, you can store and retrieve data in session state using the 'Session' object, which represents the session for the current user. The 'Session' object provides a dictionary-like interface to store and retrieve data using key-value pairs. Here's how you can store and retrieve data in session state:

Storing Data:
To store data in session state, assign a value to a key in the 'Session' object. The key can be any string value that uniquely identifies the data you want to store. Here's an example:

// Storing a string value
Session["Username"] = "JohnDoe";

// Storing an object
List<string> favoriteMovies = new List<string> { "Inception", "The Shawshank Redemption", "The Matrix" };
Session["FavoriteMovies"] = favoriteMovies;

Retrieving Data:
To retrieve data from session state, access it using the corresponding key. The retrieved value is returned as an object, so you may need to cast it to the appropriate type. Here's an example:

// Retrieving a string value
string username = (string)Session["Username"];

// Retrieving an object
List<string> favoriteMovies = (List<string>)Session["FavoriteMovies"];

In the above example, the values stored with the keys "Username" and "FavoriteMovies" are retrieved from session state and assigned to the appropriate variables.

It's important to note that when retrieving data from session state, you should ensure the key exists and that the value is of the expected type. You can use techniques such as null-checking and type-checking to handle potential exceptions or unexpected data.

Remember that the Session object is specific to each user's session. Data stored in session state is accessible only to the current user and is not shared across different users or devices. It remains available until the session expires, the user explicitly abandons the session, or the application clears the data from session state.

Additionally, it's important to use session state judiciously and avoid storing excessive data, as it can impact the performance and scalability of your application. Consider storing only essential data and leverage alternative approaches (e.g., databases, caches) for managing persistent or shared data.