CheckInternet Mixin

The CheckInternet mixin verifies device connectivity before an action executes. If there's no internet connection, the action aborts and displays a dialog with the message: "There is no Internet. Please, verify your connection."

Basic Usage

dart

class LoadText extends AppAction with CheckInternet {

  Future<AppState?> reduce() async {
    var response = await http.get('https://api.example.com/text');
    return state.copy(text: response.body);
  }
}

The mixin works by overriding the before() method. If the device lacks connectivity, it throws a UserException which triggers the standard error dialog.

Customizing the Error Message

Override connectionException() to return a custom UserException:

dart

class LoadText extends AppAction with CheckInternet {

  @override
  UserException connectionException(UserException error) {
    return UserException('Unable to load data. Check your connection.');
  }

  Future<AppState?> reduce() async {
    var response = await http.get('https://api.example.com/text');
    return state.copy(text: response.body);
  }
}

NoDialog Modifier

Use NoDialog alongside CheckInternet to suppress the automatic error dialog. This allows you to handle connectivity failures in your widgets using isFailed() and exceptionFor():

dart

class LoadText extends AppAction with CheckInternet, NoDialog {

  Future<AppState?> reduce() async {
    var response = await http.get('https://api.example.com/text');
    return state.copy(text: response.body);
  }
}

Then handle the error in your widget:

dart

Widget build(BuildContext context) {
  if (context.isWaiting(LoadText)) {
    return CircularProgressIndicator();
  }

  if (context.isFailed(LoadText)) {
    var exception = context.exceptionFor(LoadText);
    return Text('Error: ${exception?.message}');
  }

  return Text(context.state.text);
}

AbortWhenNoInternet

Use AbortWhenNoInternet for silent failure when offline. The action aborts without throwing errors or displaying dialogs—as if it had never been dispatched:

dart

class RefreshData extends AppAction with AbortWhenNoInternet {

  Future<AppState?> reduce() async {
    var response = await http.get('https://api.example.com/data');
    return state.copy(data: response.body);
  }
}

This is useful for background refreshes or non-critical operations where user notification isn't needed.

UnlimitedRetryCheckInternet

This mixin combines three capabilities: internet verification, unlimited retry with exponential backoff, and non-reentrant behavior. It's ideal for essential operations like loading startup data:

dart

class LoadAppStartupData extends AppAction with UnlimitedRetryCheckInternet {

  Future<AppState?> reduce() async {
    var response = await http.get('https://api.example.com/startup');
    return state.copy(startupData: response.body);
  }
}

Default retry parameters:

•Initial delay: 350ms
•Multiplier: 2
•Maximum delay with internet: 5 seconds
•Maximum delay without internet: 1 second

Track retry attempts via the attempts getter and customize logging through printRetries().

Mixin Compatibility

Important compatibility rules:

•CheckInternet and AbortWhenNoInternet are incompatible with each other
•Neither CheckInternet nor AbortWhenNoInternet can be combined with UnlimitedRetryCheckInternet
•CheckInternet works well with Retry, NonReentrant, Throttle, Debounce, and optimistic mixins

Testing Internet Connectivity

Two methods for simulating connectivity in tests:

Per-action simulation - Override internetOnOffSimulation within specific actions:

dart

class LoadText extends AppAction with CheckInternet {
  @override
  bool? get internetOnOffSimulation => false; // Simulate offline

  Future<AppState?> reduce() async {
    // ...
  }
}

Global simulation - Set forceInternetOnOffSimulation on the store:

dart

var store = Store<AppState>(
  initialState: AppState.initialState(),
);
store.forceInternetOnOffSimulation = false; // All actions see no internet

Limitations

These mixins only detect device connectivity status. They cannot verify:

•Internet provider functionality
•Server availability
•API endpoint reachability

For server-specific connectivity checks, implement additional validation in your action's reduce() method or before() method.

References

URLs from the documentation: