What is ViewState in ASP.NET and how does it work?

ViewState in ASP.NET is a client-side state management technique that is used to preserve the state of controls and page data across postbacks. It is a hidden field on the page that stores the state of controls in a base64-encoded format.

When an ASP.NET page is rendered, the state of controls is saved to the ViewState. This ViewState is then sent to the client as a hidden field in the rendered HTML. When a postback occurs, the ViewState data is sent back to the server, allowing the server to reconstruct the page and controls as they were before the postback.

ViewState is particularly useful for maintaining the state of controls like textboxes, dropdown lists, and checkboxes across postbacks, without the need for manually storing and retrieving values. However, ViewState can also result in larger page sizes and increased server load due to the amount of data being stored and transferred.

Overall, ViewState is a powerful feature in ASP.NET that simplifies state management and improves the user experience by maintaining control state across postbacks.