如何使用Swift 3中的UIWebview在缓存中保存动态网页

I am developing an application(Swift 3 using UIWebview). I need to load webpages into webview and save some webpages into cache. If there is not internet user will able to see those pages. But I am confused on how to save whole webpage in cache. The main thing is we need to show pages back even if there is not internet. I am developing an application(Swift 3 using UI