How to obfuscate Flutter apps?

AppBundle (recommended):

• Without splitting:

  flutter build appbundle --obfuscate --split-debug-info=/<directory>
  

• Splitting:

  flutter build appbundle --target-platform android-arm,android-arm64,android-x64 --obfuscate --split-debug-info=/<directory>
  

---

APK:

• Without splitting:

  flutter build apk --obfuscate --split-debug-info=/<directory>
  

• Splitting:

  flutter build apk --target-platform android-arm,android-arm64,android-x64 --split-per-abi --obfuscate --split-debug-info=/<directory>
  

PS: About Splitting:
By default, fat apk contains arm v7, arm v8 and x64 which increases apk size, which you don't want to. So, when you split it, you have separate binaries which you can upload on the store and thus reducing the size of the apk that a user would need to download.

Obfuscation is needed - a flutter app knows its function names, which can be shown using Dart's StackTrace class. There's under-tested support for obfuscation. To enable it:

---

For Android:
Add to the file [ProjectRoot]/android/gradle.properties :

extra-gen-snapshot-options=--obfuscate

---

For iOS:
First, edit [FlutterRoot]/packages/flutter_tools/bin/xcode_backend.sh:
Locate the build aot call, and add a flag to it,

${extra_gen_snapshot_options_or_none}

defined as:

local extra_gen_snapshot_options_or_none=""
if [[ -n "$EXTRA_GEN_SNAPSHOT_OPTIONS" ]]; then
  extra_gen_snapshot_options_or_none="--extra-gen-snapshot-options=$EXTRA_GEN_SNAPSHOT_OPTIONS"
fi

To apply your changes, in [FlutterRoot], run

git commit -am "Enable obfuscation on iOS"  
flutter  

(Running "flutter" after the commit rebuilds flutter tools.)

Next, in your project, add following to [ProjectRoot]/ios/Flutter/Release.xcconfig file:

EXTRA_GEN_SNAPSHOT_OPTIONS=--obfuscate

---

PS: Haven't tried the --save-obfuscation-map flag mentioned at https://github.com/dart-lang/sdk/issues/30524
Again, obfuscation isn't very well tested, as mentioned by @mraleph.

All the above answers are correct, but no answer tells you that we need to add a relative path or directory path while generating build.

Example using Relative Path:

flutter build apk --obfuscate --split-debug-info=./ProjectFolderName/debug
                                

Example using Folder Path:

flutter build apk --obfuscate --split-debug-info=/Users/apple/Desktop/items/debug

The above command will generate a build inside the given project directory, it will create a new folder called ProjectFolderName or 'debug' on the respective command, and there you can find the release build.