vital_bluetooth

Bluetooth LE for Flutter, built for wearables and healthcare devices that have to stay connected and keep streaming data, even while the app is in the background or its screen has been closed.

  • Background mode. Links survive the app going to the background, the screen turning off, and the app's UI being closed. A dropped link is restored in native code and notifications are turned back on. Values that arrive while no Dart code runs are kept for you.
  • Automatic reconnect. Dropped links come back with backoff, and every notification you turned on is turned on again.
  • Queued GATT operations. Reads, writes and notification changes run one at a time per device, so concurrent calls never collide.
  • Android quirks handled. GATT status 133 is retried, every connection is closed properly, and location being off on Android 7–11 is reported instead of returning an empty scan.
  • Typed errors. A sealed exception hierarchy you can switch over, with the raw native code kept for logging.
  • State-management friendly. Adapter state, scanning, connection state, services, MTU and names are ValueListenables; scans and values are Streams.

Platform support

Android iOS macOS Windows
Scan, connect, GATT, notifications ✅ ✅ ✅ ✅
Background mode ✅ ✅ ✅ ✅
Bonding from the app ✅ – – ✅
Read RSSI of a connected device ✅ ✅ ✅ –
MTU request ✅ auto auto auto
Connection priority, PHY ✅ – – –
Turn Bluetooth on ✅ – – ✅

– means the platform doesn't let apps do it. "auto" means the system negotiates the MTU itself; requestMtu returns the current value.

Bluetooth Classic (SPP) is planned.

Minimum versions: Android 7.0 (API 24), iOS 15, macOS 12, Windows 10.

Installation

dependencies:
  vital_bluetooth: ^0.1.0

Android

Nothing to add. The plugin's manifest declares:

  • Android 12+: BLUETOOTH_SCAN (with neverForLocation) and BLUETOOTH_CONNECT
  • Android 11 and lower: BLUETOOTH, BLUETOOTH_ADMIN and ACCESS_FINE_LOCATION
  • Background mode: FOREGROUND_SERVICE, FOREGROUND_SERVICE_CONNECTED_DEVICE, POST_NOTIFICATIONS and the foreground service

If your app needs to derive location from scans (beacons), remove the neverForLocation flag in your own manifest:

<uses-permission android:name="android.permission.BLUETOOTH_SCAN"
    tools:remove="android:usesPermissionFlags" />

If your app never uses background mode, you can remove its permissions and service so Google Play doesn't ask you to declare a foreground service:

<uses-permission android:name="android.permission.FOREGROUND_SERVICE_CONNECTED_DEVICE"
    tools:node="remove" />
<service android:name="dev.goodluckcy.vital_bluetooth.VitalBluetoothService"
    tools:node="remove" />

The background-mode notification uses a drawable named vital_bluetooth_notification if your app has one, and the app icon otherwise.

iOS

Add to ios/Runner/Info.plist:

<key>NSBluetoothAlwaysUsageDescription</key>
<string>Connects to your heart rate monitor.</string>
<!-- Only for background mode: -->
<key>UIBackgroundModes</key>
<array>
  <string>bluetooth-central</string>
</array>

macOS

Add NSBluetoothAlwaysUsageDescription to macos/Runner/Info.plist, and to both DebugProfile.entitlements and Release.entitlements:

<key>com.apple.security.device.bluetooth</key>
<true/>

Windows

Nothing to add.

Quick start

import 'package:vital_bluetooth/vital_bluetooth.dart';

final bluetooth = VitalBluetooth();

// 1. Permissions
final status = await bluetooth.requestPermissions();
if (!status.isGranted) return;

// 2. Scan for heart rate monitors
final result = await bluetooth
    .scan(withServices: ['180d'], timeout: const Duration(seconds: 10))
    .first;

// 3. Connect (opens the link and discovers services, with retries)
final device = result.device;
await device.connect();

// 4. Subscribe to heart rate measurements
final heartRate = device.characteristic('180d', '2a37')!;
heartRate.values.listen((bytes) => print('HR packet: $bytes'));
await heartRate.setNotify(true);

UUIDs can be written as '180d', '0x180D' or the full 128-bit form.

Staying connected in the background

final bluetooth = VitalBluetooth();

// Keep reconnecting while the app is open, with no attempt limit.
bluetooth.defaultOptions = const ConnectionOptions(
  reconnect: ReconnectPolicy.unlimited(),
);

// When the app starts: pick up links that were kept alive while it was
// closed, and store what arrived meanwhile.
final devices = await bluetooth.restoreDevices();
final missed = await bluetooth.takeBackgroundValues();
for (final v in missed) {
  saveReading(v.deviceId, v.characteristicUuid, v.value, v.timestamp);
}

// Turn it on while the app is in the foreground.
await bluetooth.enableBackgroundMode(
  title: 'Heart rate monitor',
  text: 'Connected',
);

What it does on each platform:

  • Android runs a foreground service of type connectedDevice with an ongoing notification (the system requires one). The process is kept alive, links outlive the app's screen (back button, swiping the app away from recents), and while no screen is open a dropped link is reconnected natively with autoConnect, with no time limit. Values that arrive with no screen open are buffered (the latest 10,000).
  • iOS suspends apps in the background, so Dart timers stop. A dropped link is therefore reconnected natively right away: iOS keeps the connect pending and wakes the app when the device is back. With state restoration, iOS also relaunches the app in the background for a device event after it was terminated for memory. iOS doesn't relaunch an app the user swiped away. Restoration starts at the launch after background mode was first turned on.
  • macOS and Windows don't suspend apps, so links already live as long as the app does.

Usage

Adapter and permissions

ValueListenableBuilder(
  valueListenable: bluetooth.adapterState,
  builder: (context, state, _) => Text(state.isOn ? 'On' : 'Off'),
);

await bluetooth.turnOn(); // Android shows the system prompt

Scanning

scan() starts when you listen and stops when you cancel, when the timeout passes, or when the platform ends it. Only one scan runs at a time; starting another ends the first.

final subscription = bluetooth
    .scan(mode: ScanMode.lowLatency, allowDuplicates: true)
    .listen((r) => print('${r.name} ${r.rssi} dBm'));

await subscription.cancel(); // stops the scan

Connection state

ValueListenableBuilder(
  valueListenable: device.connectionState,
  builder: (context, state, _) => Text(state.status.name),
);

Statuses: disconnected, connecting, discovering, ready, reconnecting, disconnecting.

bluetooth.device(id) returns the same object for the same ID, so a screen can be closed and opened again without losing the connection. Keep devices in your state-management layer and call disconnect() only when the user asks.

Reading and writing

final location = device.characteristic('180d', '2a38')!;
final value = await location.read();

final control = device.characteristic(serviceUuid, controlUuid)!;
await control.write([0x01, 0xA0], withResponse: true);

Every value from valuesWithTime carries the time the platform received it, which matters for signals like ECG because values reach Dart in batches:

heartRate.valuesWithTime.listen((v) => print('${v.timestamp}: ${v.value}'));

Reconnect and timeouts

final device = bluetooth.device(
  id,
  options: const ConnectionOptions(
    connectTimeout: Duration(seconds: 15),
    connectAttempts: 3,
    reconnect: ReconnectPolicy.unlimited(),
  ),
);

ReconnectPolicy() tries 5 times with exponential backoff (1 s up to 30 s). ReconnectPolicy.none() turns reconnecting off. Options apply when a device object is first created; set bluetooth.defaultOptions before scanning to cover devices created from scan results.

MTU, RSSI, bonding

await device.requestMtu(247);
final rssi = await device.readRssi();
await device.createBond();
await device.requestConnectionPriority(ConnectionPriority.high);

Check await bluetooth.getCapabilities() to see what the current platform supports before offering a feature.

Errors

All errors extend the sealed VitalBluetoothException:

try {
  await device.connect();
} on VitalBluetoothException catch (e) {
  switch (e) {
    case PermissionDeniedException(:final permanentlyDenied):
      // ask the user, or send them to the settings
    case LocationServicesDisabledException():
      // Android 7–11: ask the user to turn location on
    case GattException(requiresBonding: true):
      await device.createBond();
    case _ when e.isRetryable:
      // try again later
    default:
      print(e); // includes the native code, e.g. GATT status 133
  }
}

Example app

The example scans for nearby devices, connects, lists services, lets you read, write (hex) and subscribe to any characteristic, and has a background-mode switch that shows what arrived while the app was closed.

License

MIT

Libraries

vital_bluetooth
Bluetooth LE for wearables and healthcare devices that stays connected, including in the background.