diff --git a/lib/src/components/noticebar/brn_marquee_text.dart b/lib/src/components/noticebar/brn_marquee_text.dart
index b5e9ee02..4b6b3435 100644
--- a/lib/src/components/noticebar/brn_marquee_text.dart
+++ b/lib/src/components/noticebar/brn_marquee_text.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 import 'dart:async';
 import 'package:flutter/material.dart';
 
@@ -10,7 +8,7 @@ class BrnMarqueeText extends StatefulWidget {
   final String text;
 
   /// 文字样式
-  final TextStyle textStyle;
+  final TextStyle? textStyle;
 
   ///滚动方向，水平或者垂直
   final Axis scrollAxis;
@@ -27,16 +25,14 @@ class BrnMarqueeText extends StatefulWidget {
   double height;
 
   BrnMarqueeText({
-    @required this.text,
+    required this.text,
     this.width: 0,
     this.height: 0,
     this.timerRest: 100,
     this.textStyle,
     this.scrollAxis: Axis.horizontal,
     this.ratioOfBlankToScreen: 0.25,
-  }) : assert(
-          text != null,
-        );
+  });
 
   @override
   State<StatefulWidget> createState() {
@@ -46,26 +42,26 @@ class BrnMarqueeText extends StatefulWidget {
 
 class BrnMarqueeTextState extends State<BrnMarqueeText>
     with SingleTickerProviderStateMixin {
-  ScrollController scroController;
+  late ScrollController scroController;
   double blankWidth = 1;
   double blankHeight = 1;
   double position = 0.0;
-  Timer timer;
+  Timer? timer;
   final double _moveDistance = 3.0;
-  GlobalKey _key = null;
+  GlobalKey? _key;
 
   @override
   void initState() {
     super.initState();
     scroController = new ScrollController();
-    WidgetsBinding.instance.addPostFrameCallback((callback) {
-      var size = context?.findRenderObject()?.paintBounds?.size;
+    WidgetsBinding.instance?.addPostFrameCallback((callback) {
+      var size = context.findRenderObject()!.paintBounds.size;
       widget.width = (widget.width) > 0 ? widget.width : size.width;
       widget.height = (widget.height) > 0 ? widget.height : size.height;
 
       _key = GlobalKey();
-      if (calculateTextWith(widget.text, widget.textStyle.fontSize,
-              widget.textStyle.fontWeight, double.infinity, 1, context) >
+      if (calculateTextWith(widget.text, widget.textStyle?.fontSize,
+              widget.textStyle?.fontWeight, double.infinity, 1, context) >
           widget.width) {
         blankWidth = widget.width * widget.ratioOfBlankToScreen;
         blankHeight = widget.height * widget.ratioOfBlankToScreen;
@@ -138,10 +134,8 @@ class BrnMarqueeTextState extends State<BrnMarqueeText>
 
   @override
   void dispose() {
-    if (timer != null) {
-      timer.cancel();
-    }
-    scroController = null;
+    timer?.cancel();
+    scroController.dispose();
     super.dispose();
   }
 
@@ -164,8 +158,13 @@ class BrnMarqueeTextState extends State<BrnMarqueeText>
     );
   }
 
-  double calculateTextWith(String value, double fontSize, FontWeight fontWeight,
-      double maxWidth, int maxLines, BuildContext context) {
+  double calculateTextWith(
+      String value,
+      double? fontSize,
+      FontWeight? fontWeight,
+      double maxWidth,
+      int maxLines,
+      BuildContext context) {
     TextPainter painter = TextPainter(
 
         ///AUTO：华为手机如果不指定locale的时候，该方法算出来的文字高度是比系统计算偏小的。
diff --git a/lib/src/components/noticebar/brn_notice_bar.dart b/lib/src/components/noticebar/brn_notice_bar.dart
index 1ba2dc20..637a20d6 100644
--- a/lib/src/components/noticebar/brn_notice_bar.dart
+++ b/lib/src/components/noticebar/brn_notice_bar.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 import 'package:bruno/src/components/noticebar/brn_marquee_text.dart';
 import 'package:bruno/src/constants/brn_asset_constants.dart';
 import 'package:bruno/src/utils/brn_tools.dart';
@@ -12,7 +10,7 @@ import 'package:flutter/material.dart';
 
 class BrnNoticeBar extends StatelessWidget {
   /// 自定义左边的图标
-  final Widget leftWidget;
+  final Widget? leftWidget;
 
   /// 是否显示左边的图标
   final bool showLeftIcon;
@@ -21,30 +19,30 @@ class BrnNoticeBar extends StatelessWidget {
   final String content;
 
   /// 通知的文字颜色
-  final Color textColor;
+  final Color? textColor;
 
   /// 背景颜色
-  final Color backgroundColor;
+  final Color? backgroundColor;
 
   /// 右边的图标
-  final Widget rightWidget;
+  final Widget? rightWidget;
 
   /// 是否显示右边的图标
   /// 默认值true
   final bool showRightIcon;
 
   /// 默认样式，取[NoticeStyles]里面的值
-  final NoticeStyle noticeStyle;
+  final NoticeStyle? noticeStyle;
 
   /// 是否跑马灯
   /// 默认值false
   final bool marquee;
 
   /// 通知钮点击的回调
-  final VoidCallback onNoticeTap;
+  final VoidCallback? onNoticeTap;
 
   /// 右侧图标点击的回调
-  final VoidCallback onRightIconTap;
+  final VoidCallback? onRightIconTap;
 
   /// 最小高度。leftWidget、rightWidget 都为空时，限制的最小高度。
   /// 可以通过该属性控制组件高度，内容会自动垂直居中。
@@ -52,13 +50,13 @@ class BrnNoticeBar extends StatelessWidget {
   final double minHeight;
 
   /// 内容的内边距
-  final EdgeInsets padding;
+  final EdgeInsets? padding;
 
   const BrnNoticeBar(
-      {Key key,
+      {Key? key,
       this.leftWidget,
       this.showLeftIcon = true,
-      @required this.content,
+      required this.content,
       this.textColor,
       this.backgroundColor,
       this.rightWidget,
@@ -69,8 +67,7 @@ class BrnNoticeBar extends StatelessWidget {
       this.marquee = false,
       this.padding,
       this.minHeight = 36})
-      : assert(content != null),
-        super(key: key);
+      : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -82,7 +79,7 @@ class BrnNoticeBar extends StatelessWidget {
       tempRightWidget = GestureDetector(
         child: tempRightWidget,
         onTap: () {
-          onRightIconTap();
+          onRightIconTap!();
         },
       );
     }
@@ -91,7 +88,7 @@ class BrnNoticeBar extends StatelessWidget {
     if (marquee) {
       contentWidget = BrnMarqueeText(
         height: 36,
-        text: content ?? '',
+        text: content,
         textStyle: TextStyle(
           color:
               textColor ?? (noticeStyle?.textColor ?? defaultStyle.textColor),
@@ -100,7 +97,7 @@ class BrnNoticeBar extends StatelessWidget {
       );
     } else {
       contentWidget = Text(
-        content ?? '',
+        content,
         overflow: TextOverflow.ellipsis,
         style: TextStyle(
           color:
@@ -113,14 +110,14 @@ class BrnNoticeBar extends StatelessWidget {
     return Container(
       color: backgroundColor ??
           (noticeStyle != null
-              ? noticeStyle.backgroundColor
+              ? noticeStyle!.backgroundColor
               : defaultStyle.backgroundColor),
       padding: this.padding ?? EdgeInsets.symmetric(horizontal: 20),
       constraints: BoxConstraints(minHeight: this.minHeight),
       child: GestureDetector(
         onTap: () {
           if (onNoticeTap != null) {
-            onNoticeTap();
+            onNoticeTap!();
           }
         },
         child: Row(
diff --git a/lib/src/components/noticebar/brn_notice_bar_with_button.dart b/lib/src/components/noticebar/brn_notice_bar_with_button.dart
index 3f23a418..7e1e59fd 100644
--- a/lib/src/components/noticebar/brn_notice_bar_with_button.dart
+++ b/lib/src/components/noticebar/brn_notice_bar_with_button.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 import 'package:bruno/src/components/noticebar/brn_marquee_text.dart';
 import 'package:flutter/material.dart';
 
@@ -13,52 +11,52 @@ class BrnNoticeBarWithButton extends StatelessWidget {
   final String content;
 
   /// 通知的背景色
-  final Color backgroundColor;
+  final Color? backgroundColor;
 
   /// 通知的文字颜色
-  final Color contentTextColor;
+  final Color? contentTextColor;
 
   /// 左边标签的文字
-  final String leftTagText;
+  final String? leftTagText;
 
   /// 左边标签的文字颜色
-  final Color leftTagTextColor;
+  final Color? leftTagTextColor;
 
   /// 左边标签的背景颜色
-  final Color leftTagBackgroundColor;
+  final Color? leftTagBackgroundColor;
 
   /// 自定义左边的控件
-  final Widget leftWidget;
+  final Widget? leftWidget;
 
   ///右边按钮的文字
-  final String rightButtonText;
+  final String? rightButtonText;
 
   ///右边按钮的文字颜色
-  final Color rightButtonTextColor;
+  final Color? rightButtonTextColor;
 
   ///右边按钮的边框颜色
-  final Color rightButtonBorderColor;
+  final Color? rightButtonBorderColor;
 
   /// 自定义右边的控件
-  final Widget rightWidget;
+  final Widget? rightWidget;
 
   /// 是否跑马灯
   /// 默认值false
   final bool marquee;
 
   /// 右边按钮点击回调
-  final VoidCallback onRightButtonTap;
+  final VoidCallback? onRightButtonTap;
 
   /// 最小高度。leftWidget、rightWidget 都为空时，限制的最小高度。
   /// 可以通过该属性控制组件高度，内容会自动垂直居中。默认值 54。
   final double minHeight;
 
   /// 内容的内边距
-  final EdgeInsets padding;
+  final EdgeInsets? padding;
 
   const BrnNoticeBarWithButton(
-      {Key key,
-      @required this.content,
+      {Key? key,
+      required this.content,
       this.backgroundColor,
       this.contentTextColor,
       this.leftTagText,
@@ -73,8 +71,7 @@ class BrnNoticeBarWithButton extends StatelessWidget {
       this.rightWidget,
       this.padding,
       this.minHeight = 54})
-      : assert(content != null),
-        super(key: key);
+      : super(key: key);
 
   @override
   Widget build(BuildContext context) {
@@ -99,7 +96,7 @@ class BrnNoticeBarWithButton extends StatelessWidget {
   /// 左边的标签
   Widget _buildLeftTag() {
     if (leftWidget != null) {
-      return leftWidget;
+      return leftWidget!;
     }
 
     if (leftTagText?.isEmpty ?? true) {
@@ -115,7 +112,7 @@ class BrnNoticeBarWithButton extends StatelessWidget {
           borderRadius: BorderRadius.circular(2),
         ),
         child: Text(
-          leftTagText,
+          leftTagText!,
           style: TextStyle(
               color: leftTagTextColor ?? Colors.white,
               fontSize: 11,
@@ -127,14 +124,14 @@ class BrnNoticeBarWithButton extends StatelessWidget {
   }
 
   Widget _buildContent() {
-    if (content?.isEmpty ?? true) {
+    if (content.isEmpty) {
       return Container();
     }
 
     if (marquee) {
       return BrnMarqueeText(
         height: 20,
-        text: content ?? '',
+        text: content,
         textStyle: TextStyle(
           color: contentTextColor ?? Color(0xFF333333),
           fontSize: 14,
@@ -142,7 +139,7 @@ class BrnNoticeBarWithButton extends StatelessWidget {
       );
     } else {
       return Text(
-        content ?? '',
+        content,
         overflow: TextOverflow.ellipsis,
         style: TextStyle(
           color: contentTextColor ?? Color(0xFF333333),
@@ -155,7 +152,7 @@ class BrnNoticeBarWithButton extends StatelessWidget {
   /// 右边的按钮
   Widget _buildRightBtn() {
     if (rightWidget != null) {
-      return rightWidget;
+      return rightWidget!;
     }
 
     if (rightButtonText?.isEmpty ?? true) {
@@ -164,7 +161,7 @@ class BrnNoticeBarWithButton extends StatelessWidget {
     return GestureDetector(
       onTap: () {
         if (onRightButtonTap != null) {
-          onRightButtonTap();
+          onRightButtonTap!();
         }
       },
       child: Padding(
@@ -183,7 +180,7 @@ class BrnNoticeBarWithButton extends StatelessWidget {
             borderRadius: BorderRadius.circular(4),
           ),
           child: Text(
-            rightButtonText,
+            rightButtonText!,
             style: TextStyle(
               color: rightButtonTextColor ?? Color(0xFFFA5741),
               fontSize: 12,
diff --git a/lib/src/components/selectcity/brn_az_common.dart b/lib/src/components/selectcity/brn_az_common.dart
index 9b82fb2b..82db6329 100644
--- a/lib/src/components/selectcity/brn_az_common.dart
+++ b/lib/src/components/selectcity/brn_az_common.dart
@@ -1,19 +1,17 @@
-// @dart=2.9
-
 import 'package:flutter/material.dart';
 
 /// ISuspension Bean.
 abstract class ISuspensionBean {
-  bool isShowSuspension;
-  String name;
-  String tag; //Suspension Tag
+  bool isShowSuspension = false;
+  String name = "";
+  String tag = ""; //Suspension Tag
 }
 
 /// AzListView Header.
 class AzListViewHeader {
   AzListViewHeader({
-    @required this.height,
-    @required this.builder,
+    required this.height,
+    required this.builder,
     this.tag = "↑",
   });
 
@@ -26,7 +24,7 @@ class AzListViewHeader {
 class SuspensionUtil {
   /// sort list  by suspension tag.
   /// 根据[A-Z]排序。
-  static void sortListBySuspensionTag(List<ISuspensionBean> list) {
+  static void sortListBySuspensionTag(List<ISuspensionBean>? list) {
     if (list == null || list.isEmpty) return;
     list.sort((a, b) {
       if (a.tag == "@" || b.tag == "#") {
@@ -41,10 +39,10 @@ class SuspensionUtil {
 
   /// get index data list by suspension tag.
   /// 获取索引列表。
-  static List<String> getTagIndexList(List<ISuspensionBean> list) {
-    List<String> indexData = List();
+  static List<String> getTagIndexList(List<ISuspensionBean>? list) {
+    List<String> indexData = [];
     if (list != null && list.isNotEmpty) {
-      String tempTag;
+      String? tempTag;
       for (int i = 0, length = list.length; i < length; i++) {
         String tag = list[i].tag;
         if (tag.length > 2) tag = tag.substring(0, 2);
@@ -58,11 +56,11 @@ class SuspensionUtil {
   }
 
   /// set show suspension status.
-  static void setShowSuspensionStatus(List<ISuspensionBean> list) {
+  static void setShowSuspensionStatus(List<ISuspensionBean>? list) {
     if (list == null || list.isEmpty) return;
-    String tempTag;
+    String? tempTag;
     for (int i = 0, length = list.length; i < length; i++) {
-      String tag = list[i].tag;
+      String? tag = list[i].tag;
       if (tempTag != tag) {
         tempTag = tag;
         list[i].isShowSuspension = true;
diff --git a/lib/src/components/selectcity/brn_az_listview.dart b/lib/src/components/selectcity/brn_az_listview.dart
index 2f976e4c..5243f172 100644
--- a/lib/src/components/selectcity/brn_az_listview.dart
+++ b/lib/src/components/selectcity/brn_az_listview.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 import 'package:bruno/src/components/selectcity/brn_az_common.dart';
 import 'package:bruno/src/components/selectcity/brn_index_bar.dart';
 import 'package:bruno/src/components/selectcity/brn_suspension_view.dart';
@@ -20,7 +18,7 @@ typedef Widget IndexHintBuilder(BuildContext context, String hint);
 
 /// _Header.
 class _Header extends ISuspensionBean {
-  String tag;
+  String tag = "";
 
   String getSuspensionTag() => tag;
 
@@ -31,15 +29,15 @@ class _Header extends ISuspensionBean {
 /// AzListView.
 class AzListView extends StatefulWidget {
   AzListView(
-      {Key key,
+      {Key? key,
       this.data,
       this.topData,
-      this.itemBuilder,
+      required this.itemBuilder,
       this.controller,
       this.physics,
       this.shrinkWrap = true,
       this.padding = EdgeInsets.zero,
-      this.suspensionWidget,
+      required this.suspensionWidget,
       this.isUseRealIndex = true,
       this.itemHeight = 50,
       this.suspensionHeight = 40,
@@ -48,20 +46,19 @@ class AzListView extends StatefulWidget {
       this.indexBarBuilder,
       this.indexHintBuilder,
       this.showIndexHint = true})
-      : assert(itemBuilder != null),
-        super(key: key);
+      : super(key: key);
 
   ///with ISuspensionBean Data
-  final List<ISuspensionBean> data;
+  final List<ISuspensionBean>? data;
 
   ///with ISuspensionBean topData, Do not participate in [A-Z] sorting (such as hotList).
-  final List<ISuspensionBean> topData;
+  final List<ISuspensionBean>? topData;
 
   final ItemWidgetBuilder itemBuilder;
 
-  final ScrollController controller;
+  final ScrollController? controller;
 
-  final ScrollPhysics physics;
+  final ScrollPhysics? physics;
 
   final bool shrinkWrap;
 
@@ -80,13 +77,13 @@ class AzListView extends StatefulWidget {
   final int suspensionHeight;
 
   ///on sus tag change callback.
-  final ValueChanged<String> onSusTagChanged;
+  final ValueChanged<String>? onSusTagChanged;
 
-  final AzListViewHeader header;
+  final AzListViewHeader? header;
 
-  final IndexBarBuilder indexBarBuilder;
+  final IndexBarBuilder? indexBarBuilder;
 
-  final IndexHintBuilder indexHintBuilder;
+  final IndexHintBuilder? indexHintBuilder;
 
   final bool showIndexHint;
 
@@ -100,12 +97,12 @@ class _AzListViewState extends State<AzListView> {
   //右侧索引tag  与 距离offset的value，比如 a---0， b---item*个数，c---a+b
   Map<String, int> _suspensionSectionMap = Map();
 
-  List<ISuspensionBean> _cityList = List();
-  List<String> _indexTagList = List();
+  List<ISuspensionBean> _cityList = [];
+  List<String> _indexTagList = [];
   bool _isShowIndexBarHint = false;
   String _indexBarHint = "";
 
-  ScrollController _scrollController;
+  late ScrollController _scrollController;
 
   @override
   void initState() {
@@ -115,7 +112,7 @@ class _AzListViewState extends State<AzListView> {
 
   @override
   void dispose() {
-    _scrollController?.dispose();
+    _scrollController.dispose();
     super.dispose();
   }
 
@@ -123,7 +120,7 @@ class _AzListViewState extends State<AzListView> {
     setState(() {
       _indexBarHint = model.tag;
       _isShowIndexBarHint = model.isTouchDown;
-      int offset = _suspensionSectionMap[model.tag];
+      int? offset = _suspensionSectionMap[model.tag];
       if (offset != null) {
         _scrollController.jumpTo(offset
             .toDouble()
@@ -134,10 +131,10 @@ class _AzListViewState extends State<AzListView> {
 
   void _init() {
     _cityList.clear();
-    if (widget.topData != null && widget.topData.isNotEmpty) {
-      _cityList.addAll(widget.topData);
+    if (widget.topData != null && widget.topData!.isNotEmpty) {
+      _cityList.addAll(widget.topData!);
     }
-    List<ISuspensionBean> list = widget.data;
+    List<ISuspensionBean>? list = widget.data;
     if (list != null && list.isNotEmpty) {
 //      SuspensionUtil.sortListBySuspensionTag(list);
       _cityList.addAll(list);
@@ -146,7 +143,7 @@ class _AzListViewState extends State<AzListView> {
     SuspensionUtil.setShowSuspensionStatus(_cityList);
 
     if (widget.header != null) {
-      _cityList.insert(0, _Header()..tag = widget.header.tag);
+      _cityList.insert(0, _Header()..tag = widget.header!.tag);
     }
     _indexTagList.clear();
     if (widget.isUseRealIndex) {
@@ -171,8 +168,8 @@ class _AzListViewState extends State<AzListView> {
             itemBuilder: (BuildContext context, int index) {
               if (index == 0 && _cityList[index] is _Header) {
                 return SizedBox(
-                    height: widget.header.height.toDouble(),
-                    child: widget.header.builder(context));
+                    height: widget.header!.height.toDouble(),
+                    child: widget.header!.builder(context));
               }
               return widget.itemBuilder(context, _cityList[index]);
             }),
@@ -195,7 +192,7 @@ class _AzListViewState extends State<AzListView> {
         onTouch: _onIndexBarTouch,
       );
     } else {
-      indexBar = widget.indexBarBuilder(
+      indexBar = widget.indexBarBuilder!(
         context,
         _indexTagList,
         _onIndexBarTouch,
@@ -207,7 +204,7 @@ class _AzListViewState extends State<AzListView> {
     ));
     Widget indexHint;
     if (widget.indexHintBuilder != null) {
-      indexHint = widget.indexHintBuilder(context, '$_indexBarHint');
+      indexHint = widget.indexHintBuilder!(context, '$_indexBarHint');
     } else {
       indexHint = Card(
         color: Colors.black54,
diff --git a/lib/src/components/selectcity/brn_base_azlistview_page.dart b/lib/src/components/selectcity/brn_base_azlistview_page.dart
index a73c1027..03d23313 100644
--- a/lib/src/components/selectcity/brn_base_azlistview_page.dart
+++ b/lib/src/components/selectcity/brn_base_azlistview_page.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 import 'dart:async';
 
 import 'package:bruno/src/components/empty/brn_empty_status.dart';
@@ -27,10 +25,10 @@ abstract class BaseAZListViewPage extends StatefulWidget {
   Widget buildItemWidget(ISuspensionBean item);
 
   //悬浮的widget
-  Widget buildSuspensionWidget(String tag);
+  Widget buildSuspensionWidget(String? tag);
 
   List<ISuspensionBean> getTopData() {
-    return List<ISuspensionBean>();
+    return <ISuspensionBean>[];
   }
 
   //item的高度 默认50
@@ -41,16 +39,19 @@ abstract class BaseAZListViewPage extends StatefulWidget {
 
   //每个modal 对应的 tag，默认是拼音来设置
   String createTagByModal(ISuspensionBean bean) {
-    String pinyin = PinyinHelper.getPinyinE(bean.name);
-    return pinyin.substring(0, 1).toUpperCase();
+    if (bean.name.isNotEmpty) {
+      String pinyin = PinyinHelper.getPinyinE(bean.name);
+      return pinyin.substring(0, 1).toUpperCase();
+    }
+    return "";
   }
 }
 
 class _BaseAZListViewPageState extends State<BaseAZListViewPage> {
-  String suspensionTag = "";
+  String? suspensionTag = "";
 
-  List<ISuspensionBean> _dataList = List();
-  StreamController<String> streamController;
+  List<ISuspensionBean> _dataList = [];
+  late StreamController<String> streamController;
 
   @override
   void initState() {
@@ -72,14 +73,15 @@ class _BaseAZListViewPageState extends State<BaseAZListViewPage> {
             if (snapShot.connectionState == ConnectionState.done) {
               if (snapShot.hasError) {
                 return BrnAbnormalStateUtils.getEmptyWidgetByState(
-                    context, AbnormalState.networkConnectError,action:  (index) {
+                    context, AbnormalState.networkConnectError,
+                    action: (index) {
                   setState(() {});
                 });
               } else {
                 return buildContentBody(snapShot.data);
               }
             }
-            return null;
+            return Container();
           },
         ));
   }
@@ -98,7 +100,7 @@ class _BaseAZListViewPageState extends State<BaseAZListViewPage> {
 
     if (_dataList.isEmpty && top.isEmpty) {
       return BrnAbnormalStateUtils.getEmptyWidgetByState(
-          context, AbnormalState.noData,);
+          context, AbnormalState.noData);
     }
 
     suspensionTag = top.isEmpty ? _dataList[0].tag : top[0].tag;
@@ -109,7 +111,7 @@ class _BaseAZListViewPageState extends State<BaseAZListViewPage> {
             child: StreamBuilder(
           initialData: suspensionTag,
           stream: streamController.stream,
-          builder: (context, snapShot) {
+          builder: (context, AsyncSnapshot snapShot) {
             return AzListView(
               data: _dataList,
               topData: top,
@@ -128,14 +130,14 @@ class _BaseAZListViewPageState extends State<BaseAZListViewPage> {
     );
   }
 
-  Widget _buildSusWidget(String susTag) {
+  Widget _buildSusWidget(String? susTag) {
     return Container(
       height: widget.getSuspensionHeight(),
       child: widget.buildSuspensionWidget(susTag),
     );
   }
 
-  void _handleList(List<ISuspensionBean> list) {
+  void _handleList(List<ISuspensionBean>? list) {
     if (list == null || list.isEmpty) return;
     for (int i = 0, length = list.length; i < length; i++) {
       String tag = widget.createTagByModal(list[i]);
@@ -154,7 +156,7 @@ class _BaseAZListViewPageState extends State<BaseAZListViewPage> {
   }
 
   Widget _buildListItem(ISuspensionBean model) {
-    String susTag = model.tag;
+    String? susTag = model.tag;
     return Column(
       children: <Widget>[
         //当offstage为true，当前控件不会被绘制在屏幕上
diff --git a/lib/src/components/selectcity/brn_index_bar.dart b/lib/src/components/selectcity/brn_index_bar.dart
index e2703925..3db2109e 100644
--- a/lib/src/components/selectcity/brn_index_bar.dart
+++ b/lib/src/components/selectcity/brn_index_bar.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 import 'package:flutter/material.dart';
 
 /// IndexBar touch callback IndexModel.
@@ -7,11 +5,9 @@ typedef void IndexBarTouchCallback(IndexBarDetails model);
 
 /// IndexModel.
 class IndexBarDetails {
-  String tag; //current touch tag.
-  int position; //current touch position.
-  bool isTouchDown; //is touch down.
-
-  IndexBarDetails({this.tag, this.position, this.isTouchDown});
+  String tag = ""; //current touch tag.
+  int position = -1; //current touch position.
+  bool isTouchDown = false; //is touch down.
 }
 
 ///Default Index data.
@@ -48,9 +44,9 @@ const List<String> INDEX_DATA_DEF = const [
 /// IndexBar.
 class IndexBar extends StatefulWidget {
   IndexBar(
-      {Key key,
+      {Key? key,
       this.data = INDEX_DATA_DEF,
-      @required this.onTouch,
+      required this.onTouch,
       this.width = 30,
       this.itemHeight = 16,
       this.color = Colors.transparent,
@@ -104,14 +100,12 @@ class _SuspensionListViewIndexBarState extends State<IndexBar> {
         textStyle: widget.textStyle,
         touchDownTextStyle: widget.touchDownTextStyle,
         onTouch: (details) {
-          if (widget.onTouch != null) {
-            if (_isTouchDown != details.isTouchDown) {
-              setState(() {
-                _isTouchDown = details.isTouchDown;
-              });
-            }
-            widget.onTouch(details);
+          if (_isTouchDown != details.isTouchDown) {
+            setState(() {
+              _isTouchDown = details.isTouchDown;
+            });
           }
+          widget.onTouch(details);
         },
       ),
     );
@@ -130,30 +124,29 @@ class _IndexBar extends StatefulWidget {
   final int itemHeight;
 
   /// IndexBar text style.
-  final TextStyle textStyle;
+  final TextStyle? textStyle;
 
-  final TextStyle touchDownTextStyle;
+  final TextStyle? touchDownTextStyle;
 
   /// Item touch callback.
   final IndexBarTouchCallback onTouch;
 
   _IndexBar(
-      {Key key,
+      {Key? key,
       this.data = INDEX_DATA_DEF,
-      @required this.onTouch,
+      required this.onTouch,
       this.width = 30,
       this.itemHeight = 16,
       this.textStyle,
       this.touchDownTextStyle})
-      : assert(onTouch != null),
-        super(key: key);
+      : super(key: key);
 
   @override
   _IndexBarState createState() => _IndexBarState();
 }
 
 class _IndexBarState extends State<_IndexBar> {
-  List<int> _indexSectionList = List();
+  List<int> _indexSectionList = [];
   int _widgetTop = -1;
   int _lastIndex = 0;
   bool _widgetTopChange = false;
@@ -176,27 +169,25 @@ class _IndexBarState extends State<_IndexBar> {
     _indexSectionList.clear();
     _indexSectionList.add(0);
     int tempHeight = 0;
-    widget.data?.forEach((value) {
+    widget.data.forEach((value) {
       tempHeight = tempHeight + widget.itemHeight;
       _indexSectionList.add(tempHeight);
     });
   }
 
   _triggerTouchEvent() {
-    if (widget.onTouch != null) {
-      widget.onTouch(_indexModel);
-    }
+    widget.onTouch(_indexModel);
   }
 
   @override
   Widget build(BuildContext context) {
-    TextStyle _style = widget.textStyle;
+    TextStyle? _style = widget.textStyle;
     if (_indexModel.isTouchDown == true) {
       _style = widget.touchDownTextStyle;
     }
     _init();
 
-    List<Widget> children = List();
+    List<Widget> children = [];
     widget.data.forEach((v) {
       children.add(SizedBox(
         width: widget.width.toDouble(),
@@ -209,7 +200,7 @@ class _IndexBarState extends State<_IndexBar> {
       onVerticalDragDown: (DragDownDetails details) {
         if (_widgetTop == -1 || _widgetTopChange) {
           _widgetTopChange = false;
-          RenderBox box = context.findRenderObject();
+          RenderBox? box = context.findRenderObject() as RenderBox;
           Offset topLeftPosition = box.localToGlobal(Offset.zero);
           _widgetTop = topLeftPosition.dy.toInt();
         }
diff --git a/lib/src/components/selectcity/brn_select_city_model.dart b/lib/src/components/selectcity/brn_select_city_model.dart
index d3806cbd..d8c28a6b 100644
--- a/lib/src/components/selectcity/brn_select_city_model.dart
+++ b/lib/src/components/selectcity/brn_select_city_model.dart
@@ -1,25 +1,21 @@
-// @dart=2.9
-
 import 'package:bruno/src/components/selectcity/brn_az_common.dart';
 
 class BrnSelectCityModel extends ISuspensionBean {
-  String name;
-  String tagIndex;
-  String namePinyin;
-  String tag;
-  String cityCode;
+  String name = "";
+  String tagIndex = "";
+  String? namePinyin;
+  String tag = "";
+  String cityCode = "";
 
   BrnSelectCityModel({
-    this.name,
-    this.tagIndex,
+    required this.name,
+    this.tagIndex = "",
     this.namePinyin,
-    this.tag,
-    this.cityCode,
+    this.tag = "",
+    this.cityCode = "",
   });
 
-  BrnSelectCityModel.fromJson(Map<String, dynamic> json)
-      : name = json['name'] == null ? "" : json['name'],
-        cityCode = json['cityCode'] == null ? "" : json['cityCode'];
+  BrnSelectCityModel.fromJson(Map<String, dynamic> json);
 
   Map<String, dynamic> toJson() => {
         'name': name,
diff --git a/lib/src/components/selectcity/brn_single_select_city_page.dart b/lib/src/components/selectcity/brn_single_select_city_page.dart
index ba17a40d..8076d03a 100644
--- a/lib/src/components/selectcity/brn_single_select_city_page.dart
+++ b/lib/src/components/selectcity/brn_single_select_city_page.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 import 'dart:convert';
 
 import 'package:bruno/src/components/empty/brn_empty_status.dart';
@@ -20,10 +18,10 @@ import 'package:lpinyin/lpinyin.dart';
 /// 功能：多可以自定制导航栏文案，搜索文案信息，定位信息，右侧可快速滑动查看城市
 class BrnSingleSelectCityPage extends StatefulWidget {
   /// 页面标题，默认空
-  final String appBarTitle;
+  final String? appBarTitle;
 
   /// 热门推荐标题，默认空
-  final String hotCityTitle;
+  final String? hotCityTitle;
 
   /// 是否展示searchBar，默认 true
   final bool showSearchBar;
@@ -32,18 +30,18 @@ class BrnSingleSelectCityPage extends StatefulWidget {
   final String locationText;
 
   /// 城市列表
-  final List<BrnSelectCityModel> cityList;
+  final List<BrnSelectCityModel>? cityList;
 
   /// 热门推荐城市列表
   final List<BrnSelectCityModel> hotCityList;
 
   /// 单选项 点击的回调
-  final ValueChanged<BrnSelectCityModel> onValueChanged;
+  final ValueChanged<BrnSelectCityModel>? onValueChanged;
 
   BrnSingleSelectCityPage({
     this.appBarTitle = '',
     this.hotCityTitle = '',
-    this.hotCityList,
+    required this.hotCityList,
     this.cityList,
     this.showSearchBar = true,
     this.locationText = '',
@@ -75,7 +73,7 @@ class _BrnSingleSelectCityPageState extends State<BrnSingleSelectCityPage> {
   String _searchText = "";
 
   /// search的TextController
-  BrnSearchTextController _brnSearchTextController;
+  late BrnSearchTextController _brnSearchTextController;
 
   @override
   void initState() {
@@ -85,7 +83,7 @@ class _BrnSingleSelectCityPageState extends State<BrnSingleSelectCityPage> {
   }
 
   void _loadData() async {
-    if (widget.cityList == null || widget.cityList.isEmpty) {
+    if (widget.cityList == null || widget.cityList!.isEmpty) {
       //加载城市列表
       rootBundle
           .loadString(
@@ -100,13 +98,13 @@ class _BrnSingleSelectCityPageState extends State<BrnSingleSelectCityPage> {
         setState(() {});
       });
     } else {
-      _cityList = widget.cityList;
+      _cityList = widget.cityList!;
       _handleList(_cityList);
       setState(() {});
     }
   }
 
-  void _handleList(List<BrnSelectCityModel> list) {
+  void _handleList(List<BrnSelectCityModel>? list) {
     if (list == null || list.isEmpty) return;
     for (int i = 0, length = list.length; i < length; i++) {
       String pinyin = PinyinHelper.getPinyinE(list[i].name);
@@ -153,10 +151,12 @@ class _BrnSingleSelectCityPageState extends State<BrnSingleSelectCityPage> {
             runAlignment: WrapAlignment.start,
             spacing: 10.0,
             children: hotCityList.map((e) {
-              return OutlineButton(
-                padding: EdgeInsets.all(0),
-                borderSide: BorderSide(color: Color(0xFFF8F8F8), width: .5),
-                color: Color(0xFFF8F8F8),
+              return OutlinedButton(
+                style: OutlinedButton.styleFrom(
+                  padding: EdgeInsets.all(0),
+                  side: BorderSide(color: Color(0xFFF8F8F8), width: .5),
+                  backgroundColor: Color(0xFFF8F8F8),
+                ),
                 child: Container(
                   alignment: Alignment.center,
                   height: 36.0,
@@ -176,7 +176,7 @@ class _BrnSingleSelectCityPageState extends State<BrnSingleSelectCityPage> {
                 onPressed: () {
                   debugPrint("OnItemClick: $e");
                   if (widget.onValueChanged != null) {
-                    widget.onValueChanged(e);
+                    widget.onValueChanged!(e);
                   }
                   Navigator.pop(context, e);
                 },
@@ -188,7 +188,7 @@ class _BrnSingleSelectCityPageState extends State<BrnSingleSelectCityPage> {
     );
   }
 
-  Widget _buildSusWidget(String susTag) {
+  Widget _buildSusWidget(String? susTag) {
     return Container(
       height: _suspensionHeight.toDouble(),
       padding: const EdgeInsets.only(left: 15.0),
@@ -206,7 +206,7 @@ class _BrnSingleSelectCityPageState extends State<BrnSingleSelectCityPage> {
   }
 
   Widget _buildListItem(BrnSelectCityModel model) {
-    String susTag = model.getSuspensionTag();
+    String? susTag = model.getSuspensionTag();
     return Column(
       children: <Widget>[
         Offstage(
@@ -220,7 +220,7 @@ class _BrnSingleSelectCityPageState extends State<BrnSingleSelectCityPage> {
             onTap: () {
               debugPrint("OnItemClick: $model");
               if (widget.onValueChanged != null) {
-                widget.onValueChanged(model);
+                widget.onValueChanged!(model);
               }
               Navigator.pop(context, model);
             },
@@ -236,7 +236,7 @@ class _BrnSingleSelectCityPageState extends State<BrnSingleSelectCityPage> {
       hintText: '请输入搜索信息',
       onTextChange: (text) {
         _searchText = text;
-        _showCityStack = (text.length == 0 || text == null) ? true : false;
+        _showCityStack = text.isEmpty;
         setState(() {});
       },
       onTextCommit: (text) {
@@ -272,12 +272,13 @@ class _BrnSingleSelectCityPageState extends State<BrnSingleSelectCityPage> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
+        resizeToAvoidBottomInset: false,
         appBar: BrnAppBar(title: widget.appBarTitle ?? '城市选择'),
         body: Container(
           decoration: BoxDecoration(color: Colors.white),
           child: Column(
             children: <Widget>[
-              widget.locationText.isEmpty || widget.locationText == null
+              widget.locationText.isEmpty
                   ? Container()
                   : _buildLocationBar(widget.locationText),
               widget.showSearchBar ? _buildSearchBar() : Container(),
@@ -302,13 +303,16 @@ class _BrnSingleSelectCityPageState extends State<BrnSingleSelectCityPage> {
       headerHeight = 0;
     }
     if (_suspensionTag.isEmpty || _suspensionTag == '') {
-      _suspensionTag = _cityList.first.tag;
+      if (_cityList.isNotEmpty) {
+        _suspensionTag = _cityList.first.tag;
+      }
     }
     return Expanded(
         flex: 1,
         child: AzListView(
           data: _cityList,
-          itemBuilder: (context, model) => _buildListItem(model),
+          itemBuilder: (context, model) =>
+              _buildListItem(model as BrnSelectCityModel),
           suspensionWidget: _buildSusWidget(_suspensionTag),
           isUseRealIndex: true,
           itemHeight: _itemHeight,
diff --git a/lib/src/components/selectcity/brn_suspension_view.dart b/lib/src/components/selectcity/brn_suspension_view.dart
index a1bdabd5..34f0bcbc 100644
--- a/lib/src/components/selectcity/brn_suspension_view.dart
+++ b/lib/src/components/selectcity/brn_suspension_view.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 import 'package:bruno/src/components/selectcity/brn_az_common.dart';
 import 'package:flutter/material.dart';
 
@@ -27,27 +25,25 @@ class SuspensionView extends StatefulWidget {
   final int itemHeight;
 
   /// on sus tag change callback.
-  final ValueChanged<String> onSusTagChanged;
+  final ValueChanged<String>? onSusTagChanged;
 
   /// on sus section callback.
-  final OnSusSectionCallBack onSusSectionInited;
+  final OnSusSectionCallBack? onSusSectionInited;
 
-  final AzListViewHeader header;
+  final AzListViewHeader? header;
 
   SuspensionView({
-    Key key,
-    @required this.data,
-    @required this.contentWidget,
-    @required this.suspensionWidget,
-    @required this.controller,
+    Key? key,
+    required this.data,
+    required this.contentWidget,
+    required this.suspensionWidget,
+    required this.controller,
     this.suspensionHeight = 40,
     this.itemHeight = 50,
     this.onSusTagChanged,
     this.onSusSectionInited,
     this.header,
-  })  : assert(contentWidget != null),
-        assert(controller != null),
-        super(key: key);
+  }) : super(key: key);
 
   @override
   _SuspensionWidgetState createState() => _SuspensionWidgetState();
@@ -55,25 +51,25 @@ class SuspensionView extends StatefulWidget {
 
 class _SuspensionWidgetState extends State<SuspensionView> {
   int _suspensionTop = 0;
-  int _lastIndex;
-  int _suSectionListLength;
+  int _lastIndex = -1;
+  late int _suSectionListLength;
 
-  List<int> _suspensionSectionList = List();
+  List<int> _suspensionSectionList = [];
   Map<String, int> _suspensionSectionMap = Map();
 
   @override
   void initState() {
     super.initState();
     if (widget.header != null) {
-      _suspensionTop = -widget.header.height;
+      _suspensionTop = -widget.header!.height;
     }
-    widget.controller?.addListener(_handleScrollerListenerTick);
+    widget.controller.addListener(_handleScrollerListenerTick);
   }
 
   @override
   void dispose() {
     super.dispose();
-    widget.controller?.removeListener(_handleScrollerListenerTick);
+    widget.controller.removeListener(_handleScrollerListenerTick);
   }
 
   void _handleScrollerListenerTick() {
@@ -82,17 +78,16 @@ class _SuspensionWidgetState extends State<SuspensionView> {
     if (_index != -1 && _lastIndex != _index) {
       _lastIndex = _index;
       if (widget.onSusTagChanged != null) {
-        widget.onSusTagChanged(_suspensionSectionMap.keys.toList()[_index]);
+        widget.onSusTagChanged!(_suspensionSectionMap.keys.toList()[_index]);
       }
     }
   }
 
   int _getIndex(int offset) {
-    if (widget.header != null && offset < widget.header.height) {
-      if (_suspensionTop != -widget.header.height &&
-          widget.suspensionWidget != null) {
+    if (widget.header != null && offset < widget.header!.height) {
+      if (_suspensionTop != -widget.header!.height) {
         setState(() {
-          _suspensionTop = -widget.header.height;
+          _suspensionTop = -widget.header!.height;
         });
       }
       return 0;
@@ -104,7 +99,7 @@ class _SuspensionWidgetState extends State<SuspensionView> {
       } else {
         space = 0;
       }
-      if (_suspensionTop != space && widget.suspensionWidget != null) {
+      if (_suspensionTop != space) {
         setState(() {
           _suspensionTop = space;
         });
@@ -124,15 +119,15 @@ class _SuspensionWidgetState extends State<SuspensionView> {
   void _init() {
     _suspensionSectionMap.clear();
     int offset = 0;
-    String tag;
+    String? tag;
     if (widget.header != null) {
-      _suspensionSectionMap[widget.header.tag] = 0;
-      offset = widget.header.height;
+      _suspensionSectionMap[widget.header!.tag] = 0;
+      offset = widget.header!.height;
     }
-    widget.data?.forEach((v) {
+    widget.data.forEach((v) {
       if (tag != v.tag) {
         tag = v.tag;
-        _suspensionSectionMap.putIfAbsent(tag, () => offset);
+        _suspensionSectionMap.putIfAbsent(tag!, () => offset);
         offset = offset + widget.suspensionHeight + widget.itemHeight;
       } else {
         offset = offset + widget.itemHeight;
@@ -143,7 +138,7 @@ class _SuspensionWidgetState extends State<SuspensionView> {
       ..addAll(_suspensionSectionMap.values);
     _suSectionListLength = _suspensionSectionList.length;
     if (widget.onSusSectionInited != null) {
-      widget.onSusSectionInited(_suspensionSectionMap);
+      widget.onSusSectionInited!(_suspensionSectionMap);
     }
   }
 
@@ -153,15 +148,15 @@ class _SuspensionWidgetState extends State<SuspensionView> {
     var children = <Widget>[
       widget.contentWidget,
     ];
-    if (widget.suspensionWidget != null) {
-      children.add(Positioned(
-        ///-0.1修复部分手机丢失精度问题
-        top: _suspensionTop.toDouble() - 0.1,
-        left: 0.0,
-        right: 0.0,
-        child: widget.suspensionWidget,
-      ));
-    }
+
+    children.add(Positioned(
+      ///-0.1修复部分手机丢失精度问题
+      top: _suspensionTop.toDouble() - 0.1,
+      left: 0.0,
+      right: 0.0,
+      child: widget.suspensionWidget,
+    ));
+
     return Stack(children: children);
   }
 }