+ // Control what the system back command does.
+ OnBackPressedCallback onBackPressedCallback = new OnBackPressedCallback(true) {
+ @Override
+ public void handleOnBackPressed() {
+ // Process the different back options.
+ if (drawerLayout.isDrawerVisible(GravityCompat.START)) { // The navigation drawer is open.
+ // Close the navigation drawer.
+ drawerLayout.closeDrawer(GravityCompat.START);
+ } else if (drawerLayout.isDrawerVisible(GravityCompat.END)){ // The bookmarks drawer is open.
+ // close the bookmarks drawer.
+ drawerLayout.closeDrawer(GravityCompat.END);
+ } else if (displayingFullScreenVideo) { // A full screen video is shown.
+ // Exit the full screen video.
+ exitFullScreenVideo();
+ } else if (currentWebView.canGoBack()) { // There is at least one item in the current WebView history.
+ // Get the current web back forward list.
+ WebBackForwardList webBackForwardList = currentWebView.copyBackForwardList();
+
+ // Get the previous entry URL.
+ String previousUrl = webBackForwardList.getItemAtIndex(webBackForwardList.getCurrentIndex() - 1).getUrl();
+
+ // Apply the domain settings.
+ applyDomainSettings(currentWebView, previousUrl, false, false, false);
+
+ // Go back.
+ currentWebView.goBack();
+ } else if (tabLayout.getTabCount() > 1) { // There are at least two tabs.
+ // Close the current tab.
+ closeCurrentTab();
+ } else { // There isn't anything to do in Privacy Browser.
+ // Close Privacy Browser. `finishAndRemoveTask()` also removes Privacy Browser from the recent app list.
+ finishAndRemoveTask();
+
+ // Manually kill Privacy Browser. Otherwise, it is glitchy when restarted.
+ System.exit(0);
+ }
+ }
+ };
+
+ // Register the on back pressed callback.
+ getOnBackPressedDispatcher().addCallback(this, onBackPressedCallback);
+