How to stop firebase error in flutter app

Solution

Add: implementation 'androidx.annotation:annotation:1.0.1' to the build.gradle of firebase_auth library. I used Android Studio to see the flutter android app structure.

---

From Android Studio

Sample Code:

build.graddle(firebase_auth library):

android {
    compileSdkVersion 28

    defaultConfig {
        minSdkVersion 16
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
    lintOptions {
        disable 'InvalidPackage'
    }
    dependencies {
        api 'com.google.firebase:firebase-auth:16.0.1'
        implementation 'androidx.annotation:annotation:1.0.1'
    }
}

pubspec.yaml(dependencies)

  flutter:
    sdk: flutter
  rxdart: ^0.20.0
  firebase_core: ^0.3.0
  firebase_analytics: ^2.0.0
  firebase_auth: ^0.8.0+1
  google_sign_in: ^4.0.0

There seems to be a bug in the latest version of some of the Google plugins where they migrated to AndroidX. I've made a pull request with a fix but it likely won't be reviewed before Monday.

A workaround meanwhile is to downgrade to a working version in your pubspec. E.g. I had firebase_storage: ^1.1.0, and after looking at the changelog to identify a previous version, I changed that line to firebase_storage: 1.0.4.

You need to migrate your project to AndroidX. You can refer this link to migrate your project. And also see change logs for firebase_auth here.