When it comes to developing web applications with ASP.Net, one concept that developers often come across is ViewState. It is a mechanism that allows ASP.Net web forms to retain their state between postbacks, which is crucial for maintaining the user's input and preventing data loss.
So, the question that arises is, when exactly does ViewState get loaded in ASP.Net? To answer this, we first need to understand what ViewState is and how it works.
ViewState is essentially a hidden field that is automatically added to every ASP.Net web form. It stores the state of the page and its controls in the form of a string, which is then encrypted and sent to the client as a part of the HTML output. When the page is submitted back to the server, this encrypted string is decoded and used to restore the state of the page and its controls.
Now, coming back to our question, ViewState is loaded during the Page_Load event of the web form's life cycle. This event occurs after the page has been initialized and all the controls on the page have been created. So, by the time the Page_Load event is fired, the ViewState has already been populated with the previous state of the page.
But, what triggers a postback and causes the ViewState to be loaded? There are a few scenarios in which the ViewState gets loaded:
1. Button click or form submission: When a user clicks on a button or submits a form, a postback is triggered, and the ViewState is loaded to maintain the state of the page.
2. AutoPostBack: Some controls, such as the DropDownList, have the AutoPostBack property set to true by default. This means that whenever the user selects an item from the dropdown, a postback is triggered, and the ViewState is loaded.
3. Server-side events: The ViewState is also loaded when a server-side event, such as PageIndexChanged or SelectedIndexChanged, is fired for a control that has ViewState enabled.
It is essential to note that the ViewState is only loaded if it is enabled for the particular control or the entire page. By default, ViewState is enabled for all controls and can be disabled by setting the EnableViewState property to false.
So, why is it crucial to know when ViewState gets loaded? Well, as useful as it is for maintaining the state of the page, it can also cause performance issues if not used correctly. Since the ViewState is sent to the client and back to the server with every postback, it can increase the size of the page and affect its load time. Therefore, it is essential to be mindful of what data is being stored in the ViewState and enable it only when necessary.
In conclusion, ViewState is an essential aspect of ASP.Net web forms, and it gets loaded during the Page_Load event. It is responsible for maintaining the state of the page and its controls between postbacks. By understanding when and how ViewState gets loaded, developers can optimize its usage and improve the performance of their web applications.
