Webview problem as I press back

hello experts,
I created app Screen 1 and Screen 2
as I click a button with URL as start value
I reach to Screen 2 and webview goes to start value URL.
but as I back press I used webview can go back and it works fine…but but as I reach to stage of “start value URL” screen is blank…why initial URL is not loaded back at last stage of back press…