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Create Signed APK for Android

This guide will walk you through the process of creating a signed APK for your Flutter Android application. A signed APK is required for publishing your app to the Google Play Store or distributing it outside of debug mode.

Prerequisites​

Before you begin, make sure you have:

  • Java Development Kit (JDK) installed on your system
  • Flutter SDK properly configured
  • Your Flutter project ready for release

Step 1: Create a Keystore using Java Keytool​

First, you need to create a keystore file that will be used to sign your APK. Open your terminal or command prompt and run the following command:

keytool -genkey -v -keystore upload-keystore.jks -keyalg RSA -keysize 2048 -validity 10000 -alias upload

Command breakdown:

  • -genkey: Generates a key pair
  • -v: Verbose output
  • -keystore upload-keystore.jks: Creates a keystore file named "upload-keystore.jks"
  • -keyalg RSA: Uses RSA algorithm
  • -keysize 2048: Sets key size to 2048 bits
  • -validity 10000: Key valid for 10000 days
  • -alias upload: Sets the alias name as "upload"

When you run this command, you'll be prompted to enter:

  1. Keystore password: Choose a strong password and remember it
  2. Key password: You can use the same password as the keystore
  3. Personal information: Fill in the required fields (name, organization, etc.)

Important: Keep your keystore file and passwords secure! You'll need them for all future updates to your app.

Step 2: Create key.properties File​

Create a file named key.properties in your Flutter project's android/app/ directory with the following content:

storePassword=upload
keyPassword=upload
keyAlias=upload
storeFile=C:/Users/DcWhale/upload-keystore.jks

Property descriptions:

  • storePassword: The password you set for your keystore
  • keyPassword: The password you set for your key (usually the same as store password)
  • keyAlias: The alias name you used when creating the keystore (in this case "upload")
  • storeFile: The full path to your keystore file

Note: Replace the file path with the actual location where you saved your upload-keystore.jks file.

Security Considerations​

  • Never commit the key.properties file to version control
  • Add android/app/key.properties to your .gitignore file
  • Store your keystore file in a secure location
  • Consider using environment variables for production builds

Step 3: Build the Signed APK​

Now you can build your signed APK using the Flutter CLI:

flutter build apk

For a release build with optimizations:

flutter build apk --release

To build APK for specific architectures (reduces file size):

# Build for ARM64 devices (most modern Android devices)
flutter build apk --target-platform android-arm64

# Build for both ARM32 and ARM64
flutter build apk --split-per-abi

Step 4: Locate Your Signed APK​

After the build completes successfully, you'll find your signed APK in:

build/app/outputs/flutter-apk/app-release.apk

If you used --split-per-abi, you'll find multiple APK files:

  • app-arm64-v8a-release.apk (for 64-bit ARM devices)
  • app-armeabi-v7a-release.apk (for 32-bit ARM devices)
  • app-x86_64-release.apk (for 64-bit x86 devices)

Troubleshooting​

Common Issues​

  1. "Keystore file not found"

    • Verify the storeFile path in key.properties
    • Use absolute paths with forward slashes

  2. "Wrong keystore password"

    • Double-check your passwords in key.properties
    • Ensure you're using the correct keystore file

  3. "Key not found"

    • Verify the keyAlias matches what you used when creating the keystore
    • List aliases in your keystore: keytool -list -v -keystore upload-keystore.jks

Verification​

To verify your APK is properly signed:

# Check APK signature
jarsigner -verify -verbose -certs build/app/outputs/flutter-apk/app-release.apk

# Or use apksigner (part of Android SDK)
apksigner verify build/app/outputs/flutter-apk/app-release.apk

Best Practices​

  1. Backup your keystore: Store copies in secure, separate locations
  2. Document your signing process: Keep records of passwords and procedures
  3. Test thoroughly: Install and test the signed APK on physical devices
  4. Use ProGuard: Enable code obfuscation for production releases
  5. Version management: Increment version codes for each release

Next Steps​

After creating your signed APK:

  1. Test the APK on various devices
  2. Upload to Google Play Console for distribution
  3. Set up automated signing for CI/CD pipelines
  4. Consider App Bundle format for Play Store optimization

Your signed APK is now ready for distribution!