emulator -list-avds
emulator -avd Nexus_5X_API_26(emulator name)
// Online:
https://dartpad.dartlang.org/?null_safety=true
// In Android Studio:
In the files listbox (toolbar, name of file, 'main.dart' for ex), select:
> Edit configurations...
> +
> Dart Command Line App
Add your Dart file (my_project/lib), run.