Platform channels and permission boundaries

import 'package:flutter/services.dart';
const batteryChannel = MethodChannel('example.learning/battery');
Future<int?> readBattery() async {
  final value = await batteryChannel.invokeMethod<int>('readPercent');
  if (value == null) return null;
  if (value < 0 || value > 100) {
    throw const FormatException('Invalid battery percentage');
  }
  return value;
}

A conforming native implementation returns null or an integer from 0 through 100.

No native channel handler is supplied or executed. The expected result describes a protocol contract, not observed device output.

abstract interface class BatteryReader { Future<int?> readPercent(); }
class FakeBattery implements BatteryReader {
  FakeBattery(this.value);
  final int? value;
  @override Future<int?> readPercent() async => value;
}
Future<String> batteryLabel(BatteryReader reader) async {
  final value = await reader.readPercent();
  return value == null ? 'Unavailable' : '$value%';
}
// await batteryLabel(FakeBattery(25)) -> '25%'

The fake value 25 produces 25%; a null fake produces Unavailable.

Only application mapping is represented. The fake does not validate native registration, permissions, or codec compatibility.