I would like to use New Gradient App Bar package text on my app using the code below. I used this code before on the past version of flutter and got no problem.

      appBar: PreferredSize(
        preferredSize: const Size(85,85), // here the desired height
        child: NewGradientAppBar(
          title: const Text(
            'Project',
            style: TextStyle(
              fontStyle: FontStyle.italic,
              letterSpacing: 0.1,
              fontWeight: FontWeight.w800,
              fontFamily: 'Roboto',
              height: 1.3,
              fontSize: 50,
            ),
            textAlign: TextAlign.center,
          ),
          gradient: LinearGradient(colors: [Colors.teal.shade300, Colors.teal, Colors.teal.shade800]),

but I’m getting errors on the console when I run the project which are below.

Running Gradle task ‘assembleDebug’…
../../AppData/Local/Pub/Cache/hosted/pub.dev/new_gradient_app_bar-0.2.0/lib/new_gradient_app_bar.dart:422:21: Error: The getter ‘textTheme’ isn’t defined for the class ‘AppBarTheme’.

‘AppBarTheme’ is from ‘package:flutter/src/material/app_bar_theme.dart’ (‘/C:/flutter/packages/flutter/lib/src/material/app_bar_theme.dart’).
Try correcting the name to the name of an existing getter, or defining a getter or field named ‘textTheme’.
appBarTheme.textTheme?.headline6 ??
^^^^^^^^^
../../AppData/Local/Pub/Cache/hosted/pub.dev/new_gradient_app_bar-0.2.0/lib/new_gradient_app_bar.dart:425:21: Error: The getter ‘textTheme’ isn’t defined for the class ‘AppBarTheme’.

‘AppBarTheme’ is from ‘package:flutter/src/material/app_bar_theme.dart’ (‘/C:/flutter/packages/flutter/lib/src/material/app_bar_theme.dart’).
Try correcting the name to the name of an existing getter, or defining a getter or field named ‘textTheme’.
appBarTheme.textTheme?.bodyText2 ??
^^^^^^^^^
../../AppData/Local/Pub/Cache/hosted/pub.dev/new_gradient_app_bar-0.2.0/lib/new_gradient_app_bar.dart:580:21: Error: The getter ‘brightness’ isn’t defined for the class ‘AppBarTheme’.

‘AppBarTheme’ is from ‘package:flutter/src/material/app_bar_theme.dart’ (‘/C:/flutter/packages/flutter/lib/src/material/app_bar_theme.dart’).
Try correcting the name to the name of an existing getter, or defining a getter or field named ‘brightness’.
appBarTheme.brightness ??
^^^^^^^^^^
../../AppData/Local/Pub/Cache/hosted/pub.dev/new_gradient_app_bar-0.2.0/lib/new_gradient_app_bar.dart:581:19: Error: The getter ‘primaryColorBrightness’ isn’t defined for the class ‘ThemeData’.

‘ThemeData’ is from ‘package:flutter/src/material/theme_data.dart’ (‘/C:/flutter/packages/flutter/lib/src/material/theme_data.dart’).
Try correcting the name to the name of an existing getter, or defining a getter or field named ‘primaryColorBrightness’.
themeData.primaryColorBrightness;
^^^^^^^^^^^^^^^^^^^^^^
../../AppData/Local/Pub/Cache/hosted/pub.dev/new_gradient_app_bar-0.2.0/lib/new_gradient_app_bar.dart:591:32: Error: The getter ‘color’ isn’t defined for the class ‘AppBarTheme’.

‘AppBarTheme’ is from ‘package:flutter/src/material/app_bar_theme.dart’ (‘/C:/flutter/packages/flutter/lib/src/material/app_bar_theme.dart’).
Try correcting the name to the name of an existing getter, or defining a getter or field named ‘color’.
color: appBarTheme.color ?? themeData.primaryColor,
^^^^^
Target kernel_snapshot failed: Exception

FAILURE: Build failed with an exception.

What went wrong:
Execution failed for task ‘:app:compileFlutterBuildDebug’.

Process ‘command ‘C:flutterbinflutter.bat” finished with non-zero exit value 1

Try:

Run with –stacktrace option to get the stack trace.
Run with –info or –debug option to get more log output.
Run with –scan to get full insights.

I tried to Pub get and Pub Upgrade hoping it is a dependencies issue but still the errors doesn’t still there.