Autoscroll when keyboard open on purchase screen

lib/screens/purchase.dart

@@ -45,6 +45,8 @@ class PurchaseScreenState<T> extends BaseState<PurchaseScreen> {
   void initState() {
     loading = true;
     requestAsyncData(user);
+    buildFocusNode();
+    scrollController = new ScrollController();
     super.initState();
   }
 
@@ -54,12 +56,14 @@ class PurchaseScreenState<T> extends BaseState<PurchaseScreen> {
   }
 
   bool purchaseInProgress = false;
+  ScrollController scrollController;
   Map user;
   String card = '';
   String loyalityType = '';
   String loyalty = '';
   String bonus = '';
   List<Map> coupons = [];
+  ListView listView;
 
   @override
   Widget getScreenContent() {
@@ -119,8 +123,8 @@ class PurchaseScreenState<T> extends BaseState<PurchaseScreen> {
         )
     ));
 
-    return new Container(child: new ListView(reverse: true,
-      children: <Widget>[new Column(children: widgetList)].reversed.toList()));
+    listView = new ListView(children: widgetList, controller: scrollController);
+    return listView;
   }
 
   getBonusInputField() {
@@ -130,6 +134,7 @@ class PurchaseScreenState<T> extends BaseState<PurchaseScreen> {
         hintText: (app != 'crypto') ? StringsLocalization.bonusHint() : StringsLocalization.joysHint(),
         hintStyle: new TextStyle(color: greyTextColor, fontSize: 16.0)
       ),
+      focusNode: bonusFocusNode,
       controller: bonusController,
       onSubmitted: (String text) {
         setState(() {
@@ -206,13 +211,13 @@ class PurchaseScreenState<T> extends BaseState<PurchaseScreen> {
           hintText: getHintString(),
           hintStyle: new TextStyle(color: greyTextColor, fontSize: 16.0)),
       controller: controller,
+      focusNode: sumFocusNode,
       onSubmitted: (String text) {
         setState(() {
           controller.text = _parseSum(text);
         });
       },
-      textAlign: TextAlign.center,
-      autofocus: true);
+      textAlign: TextAlign.center);
   }
 
   requestAsyncData(Map user) async {
@@ -436,4 +441,39 @@ class PurchaseScreenState<T> extends BaseState<PurchaseScreen> {
       Navigator.of(context).pop(token);
     });
   }
+
+  FocusNode bonusFocusNode = new FocusNode();
+  FocusNode sumFocusNode = new FocusNode();
+
+  // TODO: Удалить дублирующийся код.
+  void buildFocusNode() {
+
+    sumFocusNode.addListener(() {
+      setState(() {
+
+        if (sumFocusNode.hasFocus && bonusFocusNode.hasFocus) {
+          bonusFocusNode.unfocus();
+        }
+
+        if (sumFocusNode.hasFocus) {
+          scrollController.animateTo(100.0, duration: new Duration(seconds: 1), curve: Curves.ease);
+        }
+
+      });
+    });
+
+    bonusFocusNode.addListener(() {
+      setState(() {
+
+        if (bonusFocusNode.hasFocus && sumFocusNode.hasFocus) {
+          sumFocusNode.unfocus();
+        }
+
+        if (bonusFocusNode.hasFocus) {
+          scrollController.animateTo(120.0, duration: new Duration(seconds: 1), curve: Curves.ease);
+        }
+
+      });
+    });
+  }
 }