When you assign a value to the NavigateUrl property, its value is stored in the ViewState collection.
You can see the ViewState collection as a bag that enables you to store data that you can retrieveagain after a postback. You identify values in View State using a unique key. In the example the key
equals the name of the property so it’s easy to see they belong together. Once you assign a value to a
View State property, it’s stored in the page in the hidden __VIEWSTATE field that you learned about in
Chapter 4. This means it gets sent to the browser when the page loads and it is sent back to the server
when the page is posted back again.
When the postback occurs, the code in Page_Load in the user control fi res again. Just as with the initial
request, the code accesses the NavigateUrl property in the Select Case/switch block: