[Android gradle 8.x] Could not create an instance of type com.android.build.api.variant.impl.LibraryVariantBuilderImpl.

[muhsinPlanetMedia]

Launching lib\main.dart on moto g45 5G in debug mode...
Running Gradle task 'assembleDebug'...

FAILURE: Build failed with an exception.

• What went wrong:
  A problem occurred configuring project ':flutter_unity_widget'.

Could not create an instance of type com.android.build.api.variant.impl.LibraryVariantBuilderImpl.
Namespace not specified. Specify a namespace in the module's build file. See https://d.android.com/r/tools/upgrade-assistant/set-namespace for information about setting the namespace.

 If you've specified the package attribute in the source AndroidManifest.xml, you can use the AGP Upgrade Assistant to migrate to the namespace value in the build file. Refer to https://d.android.com/r/tools/upgrade-assistant/agp-upgrade-assistant for general information about using the AGP Upgrade Assistant.

• 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 3s
Error: Gradle task assembleDebug failed with exit code 1

[Liuwe1Ye]

Do you have any solution for this problem? I meet same problem when use flutter with unity.

[timbotimbo]

The relevant part of your error is

Namespace not specified. Specify a namespace in the module's build file

When using Gradle 8.x you are required to have a namespace definition in your build.gradle files to compile the project.

Current status

• The plugin flutter_unity_widget plugin on pub.dev (2022.2.1) doesn't have this yet, but the master branch here does.
  (I don't have permission to publish pub.dev updates)
• Unity 2022.3 does not include this by default, Unity 6 does.

Unity workaround

• I added a namespace for the Unity 2022.3 export in this commit

Use the new 2022.3.0 unitypackage, or use the latest build.cs script from the unity example in the master branch.

Fluter workaround 1

• I've added a namespace to the plugin in this commit on the master branch.

So if you import the plugin in your pubspec.yaml from a git url instead of pub.dev, it should be fixed on the plugin side.

flutter_unity_widget:
    git:
      url: https://github.com/juicycleff/flutter-unity-view-widget.git
      ref: master # branch name or commit hash

Another alternative would be to try the experimental Unity 6 support

Flutter workaround 2

Override the gradle setting of the plugin in your build.gradle to add the namespace property.

//<flutter project>/android/build.gradle

// make sure this is above any use of "evaluationDependsOn" 
subprojects {
    afterEvaluate {

        if (project.plugins.hasPlugin("com.android.application")
                || project.plugins.hasPlugin("com.android.library")) {

            if (project.name == "flutter_unity_widget") {
                // override settings in the plugin
               
                project.android {
                    // add namespace if it is missing
                    if (namespace == null) {
                        namespace = project.group
                    }
                }
            }
        }
    }
}

[muhsinPlanetMedia]

Thanks