How do you pass arguments from command line to main in Flutter/Dart?

Question

How would you run a command and pass some custom arguments with Flutter/Dart so they can then be accessed in the main() call such as:

flutter run -device [my custom arg]

So then I can access it with:

void main(List<String> args) {
  print(args.toString());
}

Thank you.

Answer 1

There is no way to do that, because when you start an app on your device there are also no parameters that are passed.

If this is for development, you can pass -t lib/my_alternate_main.dart to flutter run to easily switch between different settings
where each alternate entry-point file calls the same application code with different parameters or with differently initialized global variables.

Update

For

• flutter run
• flutter build apk
• flutter build ios
• flutter drive

the --dart-define=... command line parameter was added for that purpose.

Additional key-value pairs that will be available as constants from the String.fromEnvironment, bool.fromEnvironment, int.fromEnvironment, and double.fromEnvironment constructors.

For more details see Flutter 1.17 no more Flavors, no more iOS Schemas. Command argument that changes everything

Example

const t = String.fromEnvironment("TEST");

flutter run --dart-define="TEST=from command line"

Be aware that const is required and that the variable name is case sensitive.

Answer 2

Android Studio

Adding command line arguments / environment variables to Android Studio Flutter project.

---

Edit

Run > Edit Configurations...

or click the Configuration drop-down selector

Add

Add your arguments in Additional arguments (quotes optional if no spaces) 2. Add a descriptive name if you like

Copy

Click copy button to easily add more config versions as needed

Select

Select your run Configs from drop down

Use

Using your arguments in code

e.g.

const String version = String.fromEnvironment('VERSION');

Answer 3

The arguments for the main method can be declared with the parameter --dart-entrypoint-args (short: -a), e.g.

flutter run -d linux --dart-entrypoint-args some_file.xml

Answer 4

-dart-define is working in the stable channel version 1.17

from commandline

flutter run --dart-define=myVar="some value"

in for example main.dart:

const MY_VAR = String.fromEnvironment('myVar', defaultValue: 'SOME_DEFAULT_VALUE');

Answer 5

I had the same problem, so I wrote a package and some instructions that can help.

https://pub.dev/packages/launch_args

I'm not aware of a way to pass the args via the flutter command. As far as I know, you have to first build the app via Flutter, then use the other CLIs to pass the tools.

Android

adb -s $DEVICE_ID shell am start \
  -n $ANDROID_PACKAGE/$ANDROID_ACTIVITY \
  -ez [arg name] [value] \
  -ez [arg name2] [value 2] \
  ...

iOS

$FLUTTER_HOME/bin/cache/artifacts/ios-deploy/ios-deploy --id $DEVICE_ID \
  --bundle build/ios/iphoneos/Runner.app \
  --debug \
  --args [arg name] [arg value] [arg name2] [arg value2] ...

Be sure to use the version of ios-deploy that's hosted in Flutter's cached artifacts. They must have made some tweaks to that tool vs the standard one that you can install via Homebrew because I could only get things working when I used Flutter's internal version.

Answer 6

@Janux already answered the right answer.

I just want to make a simple example:

flutter run -d linux -a my_argument

void main(List<String> args) {
  print(args); // flutter: [my_argument]
}