Flutter Run

You are running or building a Flutter app. The core idea of this skill: a bare flutter run is almost never the right command in a real project. Flavors, --dart-defines and the Flutter version all have to line up, and remembering them by hand is where the lost afternoons come from.

Put a task runner in front of flutter

Make the repo's Makefile (or melos script, or just file) the source of truth for how each app is launched, and run that. It is the only way the flags stay consistent between your machine, a teammate's, and CI.

A shape that works for a multi-app monorepo:

make setup                                  # pin Flutter (FVM) + bootstrap deps
make secrets ENV=dev PROJECT=<app>          # fetch secrets → .secrets.<app>.<env>.json (gitignored)

make dev PROJECT=<app>                      # web (Chrome), ENV=dev
make dev PROJECT=<app> PLATFORM=android     # Android, flavor applied automatically
make build PROJECT=<app> ENV=prod           # release build

Pin the SDK with FVM (fvm flutter ...) and commit .fvmrc. "Works on my machine" in Flutter is usually two different SDK minors.

Configuration: --dart-define, and the file form

App config should reach the binary through --dart-define, read back with String.fromEnvironment:

class AppEnv {
  static const baseURL = String.fromEnvironment('BASE_URL');
  static const appName = String.fromEnvironment('APP_NAME');
  static const apiKey  = String.fromEnvironment('X_API_KEY');
}

String.fromEnvironment is const and resolved at compile time. Two consequences that bite:

• A missing define is not an error — it is the empty string. An app that "can't reach the backend" is very often an empty BASE_URL, not a network problem.
• Changing a define requires a rebuild, not a hot reload.

Pass many values at once with --dart-define-from-file instead of a long chain of flags:

flutter run --dart-define-from-file=.secrets.myapp.dev.json

Keep .secrets.*.json gitignored and generate it from your secret manager (Doppler, 1Password, Vault, gcloud secrets) in a make secrets target. Have the task runner fall back to a couple of safe public defines when the file is absent, and print a loud warning — a silent fallback produces an app that launches and then misbehaves in ways that look like application bugs.

Android flavors

If the app declares product flavors, a flutter run without --flavor fails outright — flutter run cannot pick one for you. Have the task runner supply a sensible default and let it be overridden:

make dev PROJECT=<app> PLATFORM=android                    # default flavor
make dev PROJECT=<app> PLATFORM=android FLAVOR=<other>     # pin one

Where a flavor encodes more than one axis (device model × payment acquirer, free × paid, region), name it <axisA><AxisB> and derive the matching --dart-define from the flavor name in the task runner rather than asking the caller to keep two flags in sync. Apps with no flavors must not be passed --flavor at all.

Device selection

• Web → -d chrome (-d web is not a device id; that error is common).
• Android/iOS with exactly one device attached → let Flutter auto-select.
• More than one → pin it: flutter devices to list, then -d <id>.

Confirm the device is actually visible before debugging anything else — USB debugging off, or an unauthorized adb prompt on the device, looks identical to a broken toolchain.

Quality commands

flutter analyze
dart format .          # NOT `flutter format` — removed in Flutter 3.38
flutter test
flutter clean          # first thing to try on an inexplicable build failure

In a melos monorepo, run these across packages with melos exec -- <cmd>.

Troubleshooting

Rules

1. Prefer the repo's task-runner target over a hand-typed flutter run.
2. Never commit the secrets file; generate it, and gitignore the pattern.
3. A fallback for missing config must warn loudly, never fail silently.
4. Pin the Flutter SDK version in the repo.
5. Changing a --dart-define needs a rebuild — hot reload will not pick it up.