migrate scaffold from stateful to stateless

lib/scaffold/as_scaffold.dart

@@ -14,7 +14,7 @@ import 'package:ansu_ui/buttons/as_back_button.dart';
 ///title , AppBar 和 AppBarBottom 均为 `null`时不显示scaffold的AppBar
 ///
 ///只有AppBarBottom时只显示AppBarBottom中的内容
-class ASScaffold extends StatefulWidget {
+class ASScaffold extends StatelessWidget {
   ///标题，可为`String`或`Text`
   final dynamic title;
 
@@ -58,48 +58,47 @@ class ASScaffold extends StatefulWidget {
     this.floatingActionButton,
   }) : super(key: key);
 
-  @override
-  _ASScaffoldState createState() => _ASScaffoldState();
-}
+  Widget get _title {
+    if (title is String) return Text(title);
+    return title ?? SizedBox();
+  }
+
+  Widget get _appBar {
+    if (title == null && appBar == null && appBarBottom == null) return null;
+    return appBar ??
+        AppBar(
+          brightness: Brightness.light,
+          backgroundColor: kForegroundColor,
+          elevation: 0,
+          leading: leading ?? ASBackButton(),
+          actions: actions ?? [],
+          centerTitle: true,
+          title: DefaultTextStyle(
+            style: TextStyle(
+              color: kTextColor,
+              fontSize: 18.sp,
+              fontWeight: FontWeight.bold,
+            ),
+            child: _title,
+          ),
+          bottom: appBarBottom ??
+              PreferredSize(
+                child: SizedBox(),
+                preferredSize: Size.fromHeight(0),
+              ),
+        );
+  }
 
-class _ASScaffoldState extends State<ASScaffold> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      key: widget.key,
-      endDrawer: widget.endDrawer,
-      backgroundColor: widget.backgroundColor,
-      bottomNavigationBar: widget.bottomNavigationBar,
-      floatingActionButton: widget.floatingActionButton,
-      appBar: widget.title == null &&
-              widget.appBar == null &&
-              widget.appBarBottom == null
-          ? null
-          : widget.appBar ??
-              AppBar(
-                brightness: Brightness.light,
-                backgroundColor: kForegroundColor,
-                elevation: 0,
-                leading: widget.leading ?? ASBackButton(),
-                actions: widget.actions ?? [],
-                centerTitle: true,
-                title: DefaultTextStyle(
-                  style: TextStyle(
-                    color: kTextColor,
-                    fontSize: 18.sp,
-                    fontWeight: FontWeight.bold,
-                  ),
-                  child: widget.title is String
-                      ? Text(widget.title)
-                      : widget.title ?? SizedBox(),
-                ),
-                bottom: widget.appBarBottom ??
-                    PreferredSize(
-                      child: SizedBox(),
-                      preferredSize: Size.fromHeight(0),
-                    ),
-              ),
-      body: widget.body,
+      key: key,
+      endDrawer: endDrawer,
+      backgroundColor: backgroundColor,
+      bottomNavigationBar: bottomNavigationBar,
+      floatingActionButton: floatingActionButton,
+      appBar: _appBar,
+      body: body,
     );
   }
 }