Occurs when the content that is being navigated to has been found, and is available from the Content property, although it may not have completed loading.
Assembly: PresentationFramework (in PresentationFramework.dll)
You handle if you need to discover pertinent information regarding the navigation request when downloading commences. This information is available from the NavigationEventArgs object that is passed to the event handler, and includes:
The source page. When is raised, at least part of the source page's user interface (UI) tree has been parsed, and attached to target content control.
The requested uniform resource identifier (URI).
Response details (using a WebResponse object).
is not raised when the source page could not be found or loaded, in which case NavigationFailed is raised.