build.gradle

def localProperties = new Properties()
def localPropertiesFile = rootProject.file('local.properties')
if (localPropertiesFile.exists()) {
    localPropertiesFile.withReader('UTF-8') { reader ->
        localProperties.load(reader)
    }
}

// Load the build signing secrets from a local `keystore.properties` file.
// TODO(YOU): Create release keys and a `keystore.properties` file. See
// `example/README.md` for more info and `keystore.example.properties` for an
// example.
def keystorePropertiesFile = rootProject.file("keystore.properties")
def keystoreProperties = new Properties()
def configured = true
try {
    keystoreProperties.load(new FileInputStream(keystorePropertiesFile))
} catch (IOException e) {
    configured = false
    logger.error('Release signing information not found.')
}

project.ext {
    // TODO(YOU): Create release keys and a `keystore.properties` file. See
    // `example/README.md` for more info and `keystore.example.properties` for an
    // example.
    APP_ID = configured ? keystoreProperties['appId'] : "io.flutter.plugins.inapppurchaseexample.DEFAULT_DO_NOT_USE"
    KEYSTORE_STORE_FILE = configured ? rootProject.file(keystoreProperties['storeFile']) : null
    KEYSTORE_STORE_PASSWORD = keystoreProperties['storePassword']
    KEYSTORE_KEY_ALIAS = keystoreProperties['keyAlias']
    KEYSTORE_KEY_PASSWORD = keystoreProperties['keyPassword']
    VERSION_CODE = configured ? keystoreProperties['versionCode'].toInteger() : 1
    VERSION_NAME = configured ? keystoreProperties['versionName'] : "0.0.1"
}

if (project.APP_ID == "io.flutter.plugins.inapppurchaseexample.DEFAULT_DO_NOT_USE") {
    configured = false
    logger.error('Unique package name not set, defaulting to "io.flutter.plugins.inapppurchaseexample.DEFAULT_DO_NOT_USE".')
}

// Log a final error message if we're unable to create a release key signed
// build for an app configured in the Play Developer Console. Apks built in this
// condition won't be able to call any of the BillingClient APIs.
if (!configured) {
    logger.error('The app could not be configured for release signing. In app purchases will not be testable. See `example/README.md` for more info and instructions.')
}

def flutterRoot = localProperties.getProperty('flutter.sdk')
if (flutterRoot == null) {
    throw new GradleException("Flutter SDK not found. Define location with flutter.sdk in the local.properties file.")
}

apply plugin: 'com.android.application'
apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"

android {
    signingConfigs {
        release {
            storeFile project.KEYSTORE_STORE_FILE
            storePassword project.KEYSTORE_STORE_PASSWORD
            keyAlias project.KEYSTORE_KEY_ALIAS
            keyPassword project.KEYSTORE_KEY_PASSWORD
        }
    }

    compileSdkVersion 29

    lintOptions {
        disable 'InvalidPackage'
    }

    defaultConfig {
        applicationId project.APP_ID
        minSdkVersion 16
        targetSdkVersion 28
        versionCode project.VERSION_CODE
        versionName project.VERSION_NAME
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        // Google Play Billing APIs only work with apps signed for production.
        debug {
            if (configured) {
                signingConfig signingConfigs.release
            } else {
                signingConfig signingConfigs.debug
            }
        }
        release {
            if (configured) {
                signingConfig signingConfigs.release
            } else {
                signingConfig signingConfigs.debug
            }
        }
    }

    testOptions {
        unitTests.returnDefaultValues = true
    }
}

flutter {
    source '../..'
}

dependencies {
    implementation 'com.android.billingclient:billing:3.0.2'
    testImplementation 'junit:junit:4.12'
    testImplementation 'org.mockito:mockito-core:3.6.0'
    testImplementation 'org.json:json:20180813'
    androidTestImplementation 'androidx.test:runner:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.1'
}