I have to develop an e-commerce mobile app. In order to show the products into the app, I have to use a webview that point to a mobile web site. Associate to each product there is the “add to basket” button. Also this button is an element of the mobile site. In the tab bar (and not in the webview) of the mobile app there is the icon of the basket with the number of elements of the basket. How the webview can know that the user has added one or more element to the basket and send to this information to the native mobile app that can update the icon of the basket?
Javascript. You bind the WebView to your Android application with the JavascriptInterface. Here are some reference docs: Building Web Apps in WebView