I need a consistent gradient color as a whole, but I can't hide the elevation of the appbar.

  @override
  Widget build(BuildContext context) {

    Widget regionalSelectionContainer = Container(
      decoration: BoxDecoration(
          gradient: LinearGradient(colors: [
            Color(0xff1AB99D),
            Color(0xff2E2888)
          ])
        )
      );
 
    return Scaffold(
      backgroundColor: Color(0xfff2f1f8),
      appBar: GradientAppBar( //  just copy, no modification
        gradientStart: Color(0xff1AB99D),
        gradientEnd: Color(0xff2E2888),
        elevation: 0, // -----------invalid------------
        title: Text('Regional Selection', style: TextStyle(fontSize: 14)),
        centerTitle: true,
      ),
      body: Container(child: regionalSelectionContainer,)
    );
  }

I got this error

compiler message: file:///Users/conneraldrich/.pub-cache/hosted/pub.dartlang.org/gradient_app_bar-0.0.1/lib/gradient_app_bar.dart:393:18: Error: Method not found: 'AnnotatedRegion'.
compiler message:       child: new AnnotatedRegion<SystemUiOverlayStyle>(
compiler message:                  ^^^^^^^^^^^^^^^

    SystemChrome.setSystemUIOverlayStyle(SystemUiOverlayStyle.light.copyWith(
      statusBarColor:
          CustomColors.transparent, 
      statusBarIconBrightness: Brightness.light,
      statusBarBrightness: Brightness.light,
    ));

    return DefaultTabController(
      length: 2,
      child: Scaffold(
        appBar: GradientAppBar(
          title: Text('Flutter Demo Home Page'),
          gradient: LinearGradient(colors: [Colors.red, Colors.purple]),
          bottom: TabBar(tabs: <Widget>[
            Tab(
              icon: Icon(Icons.home),
              text: 'Home',
            ),
            Tab(
              icon: Icon(Icons.store),
              text: 'Store',
            )
          ]),
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                'You have pushed the button this many times:',
              ),
            ],
          ),
        ),
      ),
    );

Doctor summary (to see all details, run flutter doctor -v):
[√] Flutter (Channel master, 1.24.0-2.0.pre.98, on Microsoft Windows [Version 10.0.19041.572], locale ru-RU)
[√] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
[√] Android Studio (version 3.5)
[√] VS Code (version 1.50.1)
[√] Connected device (1 available)

• No issues found!

when I change leading by code:

leading:new IconButton(
                icon: new Image.asset(XMIcons.iback, width: 25, height: 25,),
                tooltip: 'Back',
                onPressed: () => _onBack(),
              )

or

leading: new Center(
            child: new InkWell(
              onTap: onCancel,
              child: new Image.asset(XMIcons.iback, width: 25, height: 25,),
            ),
          )

then icon not show. Please help me!

../../../development/flutter/.pub-cache/hosted/pub.dartlang.org/gradient_app_bar-0.1.3/lib/gradient_app_bar.dart:610:20: Error: The method 'ancestorRenderObjectOfType' isn't defined for the class 'BuildContext'.
 - 'BuildContext' is from 'package:flutter/src/widgets/framework.dart' ('../../../development/flutter/packages/flutter/lib/src/widgets/framework.dart').
Try correcting the name to the name of an existing method, or defining a method named 'ancestorRenderObjectOfType'.
    return context.ancestorRenderObjectOfType(const TypeMatcher<RenderSliverFloatingPersistentHeader>());
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^
Command PhaseScriptExecution failed with a nonzero exit code

Getting this error after upgrading flutter: ../../flutter/.pub-cache/hosted/pub.dartlang.org/gradient_app_bar-0.1.3/lib/gradient_app_bar.dart:407:57: Error: No named parameter with the name 'nullOk'. final ScaffoldState scaffold = Scaffold.of(context, nullOk: true); ^^^^^^ ../../flutter/packages/flutter/lib/src/material/scaffold.dart:1918:24: Context: Found this candidate, but the arguments don't match. static ScaffoldState of(BuildContext context) { ^^

Command PhaseScriptExecution failed with a nonzero exit code
note: Using new build system
note: Building targets in parallel
note: Planning build
note: Constructing build description

Flutter doctor: [✓] Flutter (Channel master, 1.24.0-4.0.pre.160, on Mac OS X 10.15.7 19H2 darwin-x64, locale en-AU) • Flutter version 1.24.0-4.0.pre.160 at /Users/Josh/Developer/flutter • Framework revision 678f3cb4fb (39 minutes ago), 2020-10-29 16:26:16 -0700 • Engine revision 073263e39d • Dart version 2.11.0 (build 2.11.0-260.0.dev)

[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.3) • Android SDK at /Users/Josh/Library/Android/sdk • Platform android-29, build-tools 29.0.3 • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593) • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 12.0.1) • Xcode at /Applications/Xcode.app/Contents/Developer • Xcode 12.0.1, Build version 12A7300 • CocoaPods version 1.9.1

[✓] Android Studio (version 4.1) • Android Studio at /Applications/Android Studio.app/Contents • Flutter plugin can be installed from: 🔨 https://plugins.jetbrains.com/plugin/9212-flutter • Dart plugin can be installed from: 🔨 https://plugins.jetbrains.com/plugin/6351-dart • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593)

[✓] Connected device (1 available) • iPhone 11 (mobile) • 056B5D12-1B8A-4639-BC21-1DA9FD02A58A • ios • com.apple.CoreSimulator.SimRuntime.iOS-14-0 (simulator)

• No issues found! Process finished with exit code 0

Getting this error after upgrading flutter: ../../flutter/.pub-cache/hosted/pub.dartlang.org/gradient_app_bar-0.1.3/lib/gradient_app_bar.dart:407:57: Error: No named parameter with the name 'nullOk'. final ScaffoldState scaffold = Scaffold.of(context, nullOk: true); ^^^^^^ ../../flutter/packages/flutter/lib/src/material/scaffold.dart:1918:24: Context: Found this candidate, but the arguments don't match. static ScaffoldState of(BuildContext context) { ^^

Command PhaseScriptExecution failed with a nonzero exit code
note: Using new build system
note: Building targets in parallel
note: Planning build
note: Constructing build description

Flutter doctor: [✓] Flutter (Channel master, 1.24.0-4.0.pre.160, on Mac OS X 10.15.7 19H2 darwin-x64, locale en-AU) • Flutter version 1.24.0-4.0.pre.160 at /Users/Josh/Developer/flutter • Framework revision 678f3cb4fb (39 minutes ago), 2020-10-29 16:26:16 -0700 • Engine revision 073263e39d • Dart version 2.11.0 (build 2.11.0-260.0.dev)

[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.3) • Android SDK at /Users/Josh/Library/Android/sdk • Platform android-29, build-tools 29.0.3 • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593) • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 12.0.1) • Xcode at /Applications/Xcode.app/Contents/Developer • Xcode 12.0.1, Build version 12A7300 • CocoaPods version 1.9.1

[✓] Android Studio (version 4.1) • Android Studio at /Applications/Android Studio.app/Contents • Flutter plugin can be installed from: 🔨 https://plugins.jetbrains.com/plugin/9212-flutter • Dart plugin can be installed from: 🔨 https://plugins.jetbrains.com/plugin/6351-dart • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593)

[✓] Connected device (1 available) • iPhone 11 (mobile) • 056B5D12-1B8A-4639-BC21-1DA9FD02A58A • ios • com.apple.CoreSimulator.SimRuntime.iOS-14-0 (simulator)

• No issues found! Process finished with exit code 0