Simplify page transition code

This way each time we can just use pushNamed instead of having to
construct the MaterialPageRoute each time.

lib/app.dart

@@ -4,6 +4,7 @@ import 'package:device_info/device_info.dart';
 import 'package:firebase_analytics/observer.dart';
 import 'package:flutter/material.dart';
 import 'package:gitjournal/analytics.dart';
+import 'package:gitjournal/screens/folder_listing.dart';
 import 'package:gitjournal/screens/purchase_screen.dart';
 import 'package:gitjournal/screens/purchase_thankyou_screen.dart';
 import 'package:gitjournal/utils/logger.dart';
@@ -154,18 +155,50 @@ class JournalApp extends StatelessWidget {
       theme: themeData,
       navigatorObservers: <NavigatorObserver>[JournalApp.observer],
       initialRoute: initialRoute,
-      routes: {
-        '/': (context) => HomeScreen(),
-        '/settings': (context) => SettingsScreen(),
-        '/setupRemoteGit': (context) =>
-            GitHostSetupScreen(stateContainer.completeGitHostSetup),
-        '/onBoarding': (context) =>
-            OnBoardingScreen(stateContainer.completeOnBoarding),
-        '/purchase': (context) => PurchaseScreen(),
-        '/purchase_thank_you': (context) => PurchaseThankYouScreen(),
-      },
       debugShowCheckedModeBanner: false,
       //debugShowMaterialGrid: true,
+      onGenerateRoute: (settings) {
+        if (settings.name == '/folders') {
+          return PageRouteBuilder(
+            settings: settings,
+            pageBuilder: (_, __, ___) =>
+                _screenForRoute(settings.name, stateContainer),
+            transitionsBuilder: (_, anim, __, child) {
+              return FadeTransition(opacity: anim, child: child);
+            },
           );
         }
+
+        return MaterialPageRoute(
+          settings: settings,
+          builder: (context) => _screenForRoute(
+            settings.name,
+            stateContainer,
+          ),
+        );
+      },
+    );
+  }
+
+  Widget _screenForRoute(String route, StateContainer stateContainer) {
+    switch (route) {
+      case '/':
+        return HomeScreen();
+      case '/folders':
+        return FolderListingScreen();
+      case '/settings':
+        return SettingsScreen();
+      case '/setupRemoteGit':
+        return GitHostSetupScreen(stateContainer.completeGitHostSetup);
+      case '/onBoarding':
+        return OnBoardingScreen(stateContainer.completeOnBoarding);
+      case '/purchase':
+        return PurchaseScreen();
+      case '/purchase_thank_you':
+        return PurchaseThankYouScreen();
+    }
+
+    assert(false, "Not found named route in _screenForRoute");
+    return null;
+  }
 }

lib/widgets/app_drawer.dart

@@ -8,13 +8,11 @@ import 'package:launch_review/launch_review.dart';
 import 'package:provider/provider.dart';
 import 'package:share/share.dart';
 import 'package:url_launcher/url_launcher.dart';
-import 'package:page_transition/page_transition.dart';
 import 'package:fetch_app_logs/fetch_app_logs.dart';
 
 import 'package:gitjournal/analytics.dart';
 import 'package:gitjournal/state_container.dart';
 import 'package:gitjournal/utils.dart';
-import 'package:gitjournal/screens/folder_listing.dart';
 
 class AppDrawer extends StatelessWidget {
   @override
@@ -105,14 +103,7 @@ class AppDrawer extends StatelessWidget {
               var m = ModalRoute.of(context);
               if (m.settings.name == '/') {
                 Navigator.pop(context);
-                Navigator.push(
-                  context,
-                  PageTransition(
-                    type: PageTransitionType.fade,
-                    child: FolderListingScreen(),
-                    settings: const RouteSettings(name: '/folders'),
-                  ),
-                );
+                Navigator.pushNamed(context, '/folders');
               } else if (m.settings.name == '/folders') {
                 Navigator.pop(context);
               } else {
@@ -126,14 +117,7 @@ class AppDrawer extends StatelessWidget {
                   },
                 );
                 if (!wasParent) {
-                  Navigator.push(
-                    context,
-                    PageTransition(
-                      type: PageTransitionType.fade,
-                      child: FolderListingScreen(),
-                      settings: const RouteSettings(name: '/folders'),
-                    ),
-                  );
+                  Navigator.pushNamed(context, '/folders');
                 }
               }
             },

pubspec.lock

@@ -553,13 +553,6 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.0.10"
-  page_transition:
-    dependency: "direct main"
-    description:
-      name: page_transition
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "1.1.5"
   path:
     dependency: "direct main"
     description:

pubspec.yaml

@@ -29,7 +29,6 @@ dependencies:
   fimber: ^0.3.0
   dynamic_theme: ^1.0.0
   flutter_staggered_grid_view: ^0.3.0
-  page_transition: "^1.1.5"
   provider: ^3.2.0
   git_bindings: ^0.0.12
   dart_git: