flutter showing error while creating a release build - flutter

Question

I am trying to build release apk in flutter its showing error
* What went wrong:
A problem occurred evaluating project ':app'.
> Could not find which method <init>() to invoke from this list:
its showing this error on line keystoreProperties.load(new FileInputStream(keystoreProperties))
I have key.properties file in android folder.
Mybuild.gradle
def localProperties = new Properties()
def localPropertiesFile = rootProject.file('local.properties')
if (localPropertiesFile.exists()) {
localPropertiesFile.withReader('UTF-8') { reader ->
localProperties.load(reader)
}
}
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.")
}
def flutterVersionCode = localProperties.getProperty('flutter.versionCode')
if (flutterVersionCode == null) {
flutterVersionCode = '1'
}
def flutterVersionName = localProperties.getProperty('flutter.versionName')
if (flutterVersionName == null) {
flutterVersionName = '1.0'
}
apply plugin: 'com.android.application'
apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
def keystoreProperties = new Properties()
def keystorePropertiesFile = rootProject.file('key.properties')
if (keystorePropertiesFile.exists()) {
keystoreProperties.load(new FileInputStream(keystoreProperties))
}
android {
compileSdkVersion 28
lintOptions {
disable 'InvalidPackage'
}
defaultConfig {
// TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
applicationId "com.lunchbox_admin"
minSdkVersion 18
targetSdkVersion 28
versionCode flutterVersionCode.toInteger()
versionName flutterVersionName
}
signingConfigs {
release {
keyAlias keystoreProperties['key']
keyPassword keystoreProperties['android']
storeFile keystoreProperties['storeFile'] ? file(keystoreProperties['storeFile']) : null
storePassword keystoreProperties['android']
}
}
buildTypes {
release {
// TODO: Add your own signing config for the release build.
// Signing with the debug keys for now, so `flutter run --release` works.
signingConfig signingConfigs.debug
}
}
}
flutter {
source '../..'
}
key.properties
storePassword=android
keyPassword=android
keyAlias=key
storeFile=C:/Users/asus/lunch.jks

Answer 1

if u r trying to generate release apk then change this line
buildTypes {
release {
// TODO: Add your own signing config for the release build.
// Signing with the debug keys for now, so `flutter run --release` works.
signingConfig signingConfigs.debug
}
}
to release one
buildTypes {
release {
// TODO: Add your own signing config for the release build.
// Signing with the debug keys for now, so `flutter run --release` works.
signingConfig signingConfigs.release
}
}
follow this steps carefully if u got some other errors
https://flutter.dev/docs/deployment/android