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Please watch: "How to add Facebook Banner Ad in Android Application"
you will learn about how to show No Internet Connection Dialog.
It is very pretty simple though.
Showing No Internet Connection Dialog is very helpful in app like WebView app and all other apps which are mainly dependent on Internet to work.
Making this is very easy and just take few minutes.
Link for code: http://androidmkab.com/2017/01/24/show-no-internet-connection-dialog-android/