refactor: extract loading widget

lib/widgets/issue_pull_request.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/cupertino.dart';
 import '../widgets/widgets.dart';
+import '../widgets/loading.dart';
 
 // Widget of issue screen and pull request screen
 class IssuePullRequestScreen extends StatefulWidget {
@@ -39,7 +40,7 @@ class _IssuePullRequestScreenState extends State<IssuePullRequestScreen> {
 
   Widget _buildBody(BuildContext context) {
     if (payload == null) {
-      return CupertinoActivityIndicator();
+      return Loading();
     }
 
     List items = payload['timeline']['nodes'];

lib/widgets/loading.dart

@@ -0,0 +1,39 @@
+import 'package:flutter/material.dart';
+import 'package:flutter/cupertino.dart';
+import '../providers/settings.dart';
+
+class Loading extends StatelessWidget {
+  final bool more;
+
+  Loading({this.more});
+
+  Widget _buildIndicator(BuildContext context) {
+    switch (SettingsProvider.of(context).layout) {
+      case LayoutMap.cupertino:
+        return CupertinoActivityIndicator(radius: 12);
+      default:
+        return Center(
+          child: SizedBox(
+            width: 24,
+            height: 24,
+            child: CircularProgressIndicator(),
+          ),
+        );
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    if (more) {
+      return Padding(
+        padding: EdgeInsets.symmetric(vertical: 20),
+        child: _buildIndicator(context),
+      );
+    } else {
+      return Padding(
+        padding: EdgeInsets.symmetric(vertical: 40),
+        child: _buildIndicator(context),
+      );
+    }
+  }
+}