I can't build a Flutter apk because access 'FlutterEngine' class

Question

For a couple of weeks, I can't build an apk from my project because of incompatibilities of some libraries version and Flutter. So I updated everything, but there are some errors.

This time, the error is that:

• flutter build apk

Running Gradle task 'assembleRelease'...
Running Gradle task 'assembleRelease'... Done                      28,3s
The build failed likely due to AndroidX incompatibilities in a plugin. The tool is about to try using Jetifier to solve the incompatibility.
Building plugin clipboard_manager...
Running Gradle task 'assembleAarRelease'...
Running Gradle task 'assembleAarRelease'... Done                    4,1s
√ Built build\app\outputs\repo.
Building plugin connectivity...
Running Gradle task 'assembleAarRelease'...
Running Gradle task 'assembleAarRelease'... Done                    3,3s
√ Built build\app\outputs\repo.
Building plugin package_info...
Running Gradle task 'assembleAarRelease'...
Running Gradle task 'assembleAarRelease'... Done                    3,6s
√ Built build\app\outputs\repo.
Building plugin shared_preferences...
Running Gradle task 'assembleAarRelease'...
Running Gradle task 'assembleAarRelease'... Done                    4,8s
√ Built build\app\outputs\repo.
e: C:\Trabalho\Projetos\MyProject\android\app\src\main\kotlin\com\example\MyProject\MainActivity.kt: (3, 28): Unresolved reference: NonNull
e: C:\Trabalho\Projetos\MyProject\android\app\src\main\kotlin\com\example\MyProject\MainActivity.kt: (4, 19): Unresolved reference: embedding
e: C:\Trabalho\Projetos\MyProject\android\app\src\main\kotlin\com\example\MyProject\MainActivity.kt: (5, 19): Unresolved reference: embedding
e: C:\Trabalho\Projetos\MyProject\android\app\src\main\kotlin\com\example\MyProject\MainActivity.kt: (8, 21): Unresolved reference: FlutterActivity
e: C:\Trabalho\Projetos\MyProject\android\app\src\main\kotlin\com\example\MyProject\MainActivity.kt: (9, 5): 'configureFlutterEngine' overrides nothing
e: C:\Trabalho\Projetos\MyProject\android\app\src\main\kotlin\com\example\MyProject\MainActivity.kt: (9, 42): Unresolved reference: NonNull
e: C:\Trabalho\Projetos\MyProject\android\app\src\main\kotlin\com\example\MyProject\MainActivity.kt: (9, 65): Unresolved reference: FlutterEngine
e: C:\Trabalho\Projetos\MyProject\android\app\src\main\kotlin\com\example\MyProject\MainActivity.kt: (10, 35): Cannot access class 'FlutterEngine'. Check your module classpath for missing or conflicting dependencies

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:compileReleaseKotlin'.
> Compilation error. See log for more details

* 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 17s
Running Gradle task 'assembleRelease'...
Running Gradle task 'assembleRelease'... Done                      18,5s
Gradle task assembleRelease failed with exit code 1

The error above mention the Kotlin file MainActivity.kt , so that is a copy of my file:

package com.targetsistemas.target_mlog2

import androidx.annotation.NonNull;
import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine
import io.flutter.plugins.GeneratedPluginRegistrant

class MainActivity: FlutterActivity() {
    override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
        GeneratedPluginRegistrant.registerWith(flutterEngine);
    }
}

• flutter doctor -v

[√] Flutter (Channel dev, 2.1.0-12.1.pre, on Microsoft Windows [versão 10.0.19042.867], locale pt-BR)
    • Flutter version 2.1.0-12.1.pre at C:\Flutter
    • Framework revision 8264cb3e8a (3 weeks ago), 2021-03-10 12:37:57 -0800
    • Engine revision 711ab3fda0
    • Dart version 2.13.0 (build 2.13.0-116.0.dev)

[√] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at C:\Users\israel.gomes\AppData\Local\Android\Sdk
    • Platform android-30, build-tools 30.0.2
    • ANDROID_HOME = C:\Users\israel.gomes\AppData\Local\Android\Sdk
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)
    • All Android licenses accepted.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[√] Android Studio (version 4.0)
    • Android Studio at C:\Program Files\Android\Android Studio
    • 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-b01)

[√] IntelliJ IDEA Community Edition (version 2020.3)
    • IntelliJ at C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2020.2.3
    • Flutter plugin version 55.0.4
    • Dart plugin version 203.7759

[√] VS Code (version 1.55.0)
    • VS Code at C:\Users\israel.gomes\AppData\Local\Programs\Microsoft VS Code
    • Flutter extension version 3.20.0

[√] Connected device (3 available)
    • Android SDK built for x86 (mobile) • emulator-5554 • android-x86    • Android 7.1.1 (API 25) (emulator)
    • Chrome (web)                       • chrome        • web-javascript • Google Chrome 89.0.4389.114
    • Edge (web)                         • edge          • web-javascript • Microsoft Edge 87.0.664.75

• No issues found!

Answer 1

Try the following.

1. delete the entire.gradle folder and install android dependency via android studio sync options
2. restarted android studio (invalidate cache as well).
3. in android studio menu > Build > clean project, then Build > Rebuild project