While running the app i got this error

[mithun1302]

/E:/flutter/.pub-cache/hosted/pub.dartlang.org/country_pickers-1.3.0/lib/utils/my_alert_dialog.dart:139:36: Error: Method not found: 'ButtonTheme.bar'.
children.add(new ButtonTheme.bar(
^^^

FAILURE: Build failed with an exception.

• Where:
  Script 'E:\flutter\packages\flutter_tools\gradle\flutter.gradle' line: 1035

• What went wrong:
  Execution failed for task ':app:compileFlutterBuildDebug'.

Process 'command 'E:\flutter\bin\flutter.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.

• Get more help at https://help.gradle.org

BUILD FAILED in 1m 6s
Exception: Gradle task assembleDebug failed with exit code 1

[ChetanShahapurkar]

I solved it-
In your pubspec.yaml file

change the package

from

country_pickers: ^1.3.0

To

country_pickers: ^2.0.0