要自定义引导图标，您可能需要模仿AppBar小部件的功能，该小部件根据当前上下文正确地处理显示后退按钮、抽屉图标或关闭图标。下面是一个替换默认图标的例子。

import 'package:flutter/material.dart';

class TopBar extends StatelessWidget with PreferredSizeWidget {
  static const double _topBarHeight = 60;

  @override
  Widget build(BuildContext context) {
    return AppBar(
      toolbarHeight: _topBarHeight,
      title: Text('Title'),
      automaticallyImplyLeading: false,
      leading: _buildLeadingWidget(context),
    );
  }

  @override
  Size get preferredSize => Size.fromHeight(_topBarHeight);

  Widget _buildLeadingWidget(BuildContext context) {
    final ScaffoldState scaffold = Scaffold.of(context);
    final ModalRoute<dynamic> parentRoute = ModalRoute.of(context);

    final bool canPop = ModalRoute.of(context)?.canPop ?? false;
    final bool hasDrawer = scaffold?.hasDrawer ?? false;
    final bool useCloseButton = parentRoute is PageRoute<dynamic> && parentRoute.fullscreenDialog;

    Widget leading;
    if (hasDrawer) {
      leading = IconButton(
        icon: const Icon(Icons.menu_rounded),
        onPressed: Scaffold.of(context).openDrawer,
        tooltip: MaterialLocalizations.of(context).openAppDrawerTooltip,
      );
    } else {
      if (canPop) {
        if (useCloseButton) {
          leading = IconButton(
              color: Theme.of(context).colorScheme.onBackground,
              icon: Icon(Icons.close_rounded),
              onPressed: () => Navigator.of(context).maybePop());
        } else {
          leading = IconButton(
              padding: EdgeInsets.all(0),
              iconSize: 38,
              icon: Icon(Icons.chevron_left_rounded),
              onPressed: Navigator.of(context).pop);
        }
      }
    }

    return leading;
  }
}

这个类使用PreferredSizeWidget作为一个mixin，因此您可以使用它来替换脚手架中现有的AppBar小部件。请注意_buildLeadingWidget方法，它只在必要时显示后退按钮，如果有抽屉，则显示菜单按钮，如果显示全屏对话框，则显示关闭按钮。

在AppBar中，添加前导参数并分配BackButton小部件。然后将颜色参数添加到BackButton，如下所示:

AppBar(
  leading: const BackButton(
    color: Colors.black, // Change the color here
  ),
  centerTitle: true,
)

更改CupertinoPageScaffold的主色调

Theme(
  data: Theme.of(context).copyWith(
    cupertinoOverrideTheme: CupertinoThemeData(
      scaffoldBackgroundColor: Colors.white70,
      primaryColor: Styles.green21D877, // HERE COLOR OF LEADING
    ),
  ),
  child: CupertinoPageScaffold(
    navigationBar: CupertinoNavigationBar(
      brightness: Brightness.light,
      backgroundColor: Colors.white,
      middle: Text('Cupertino App Bar'),
    ),
    child: Container(
      child: Center(
        child: CupertinoActivityIndicator(),
      ),
    ),
  ),
)

  appBar: AppBar(
          iconTheme: IconThemeData(
            color: Colors.white, //modify arrow color from here..
          ),
      );

你可以像下面这样使用iconTheme:

iconTheme: IconThemeData(
  color: Colors.black, // <= You can change your color here.
),

你可以自定义AppBarWidget，关键字with是重要的，或者你可以将你的自定义AppBarWidget分配给脚手架的appBar属性:

import 'package:flutter/material.dart';

double _getAppBarTitleWidth(
    double screenWidth, double leadingWidth, double tailWidth) {
  return (screenWidth - leadingWidth - tailWidth);
}

class AppBarWidget extends StatelessWidget with PreferredSizeWidget {
  AppBarWidget(
      {Key key,
      @required this.leadingChildren,
      @required this.tailChildren,
      @required this.title,
      this.leadingWidth: 110,
      this.tailWidth: 30})
      : super(key: key);

  final List<Widget> leadingChildren;
  final List<Widget> tailChildren;
  final String title;
  final double leadingWidth;
  final double tailWidth;

  @override
  Widget build(BuildContext context) {
    // Get screen size
    double _screenWidth = MediaQuery.of(context).size.width;

    // Get title size
    double _titleWidth =
        _getAppBarTitleWidth(_screenWidth, leadingWidth, tailWidth);

    double _offsetToRight = leadingWidth - tailWidth;

    return AppBar(
      title: Row(
        children: [
          Container(
            width: leadingWidth,
            child: Row(
              mainAxisAlignment: MainAxisAlignment.start,
              children: leadingChildren,
            ),
          ),
          Container(
            color: Colors.green,
            width: _titleWidth,
            padding: const EdgeInsets.only(left: 5.0, right: 5),
            child: Container(
              padding: EdgeInsets.only(right: _offsetToRight),
              color: Colors.deepPurpleAccent,
              child: Center(
                child: Text('$title'),
              ),
            ),
          ),
          Container(
            color: Colors.amber,
            width: tailWidth,
            child: Row(
              children: tailChildren,
            ),
          )
        ],
      ),
      titleSpacing: 0.0,
    );
  }

  @override
  Size get preferredSize => Size.fromHeight(kToolbarHeight);
}

下面是它的使用示例:

import 'package:flutter/material.dart';
import 'package:seal_note/ui/Detail/DetailWidget.dart';
import 'package:seal_note/ui/ItemListWidget.dart';

import 'Common/AppBarWidget.dart';
import 'Detail/DetailPage.dart';

class MasterDetailPage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _MasterDetailPageState();
}

class _MasterDetailPageState extends State<MasterDetailPage> {
  @override
  Widget build(BuildContext context) { 
    return Scaffold(
      appBar: AppBarWidget(leadingChildren: [
        IconButton(
          icon: Icon(
            Icons.arrow_back_ios,
            color: Colors.white,
          ),
        ),
        Text(
          '文件夹',
          style: TextStyle(fontSize: 14.0),
        ),
      ], tailChildren: [
        Icon(Icons.book),
        Icon(Icons.hd),
      ], title: '英语知识',leadingWidth: 140,tailWidth: 50,),
      body: Text('I am body'),
    );
  }
}