Scan for devices

Two ways to find a device: collect a scan, or watch results arrive one at a time.

Install#

flutter pub add flutter_classic_bluetooth

import 'package:flutter_classic_bluetooth/flutter_classic_bluetooth.dart';

The simple way#

scan runs discovery for a fixed window and hands back a finished list, deduplicated by address and sorted strongest signal first.

final bluetooth = FlutterClassicBluetooth();

final devices = await bluetooth.scan(timeout: const Duration(seconds: 10));

for (final device in devices) {
  print('${device.displayName}  ${device.address}  ${device.rssi} dBm');
}

Discovery is stopped for you when the window closes, including if something throws partway through.

A live list#

Ten seconds of a blank screen is a poor experience. Listen to discoveryResults and show each device the moment it appears.

final found = <String, BtcDevice>{};

final sub = bluetooth.discoveryResults.listen((device) {
  setState(() => found[device.address] = device);
});

await bluetooth.startDiscovery();
// ... later
await bluetooth.stopDiscovery();
await sub.cancel();

Key the map by address. The same device is reported several times during a scan, once per inquiry response, and each report may carry a different RSSI or fill in a name the first one lacked.

Knowing when it stops#

Discovery ends on its own after the platform's inquiry window, whether or not you call stopDiscovery. discoveryState tells you when that happens so a spinner can stop spinning.

bluetooth.discoveryState.listen((scanning) {
  setState(() => isScanning = scanning);
});

Devices you already know#

Most of the time the device is already paired, and a scan is wasted effort. Paired devices are available instantly, with no permission prompt on most platforms and no radio activity.

final paired = await bluetooth.getPairedDevices();

final printer = paired.firstWhere(
  (d) => d.name?.contains('Printer') ?? false,
);

A good device picker shows paired devices first and offers a scan for anything new.

What a result carries#

Use displayName in your UI. A device that has not reported a name yet would otherwise render as an empty row.

Filtering to serial devices#

A scan picks up headphones, keyboards and watches along with the board you care about. Where uuids is populated you can narrow the list to devices offering a serial port.

final serial = devices.where(
  (d) => d.uuids.any((u) => u.toUpperCase() == BtcUuid.spp),
);

Do not rely on this alone. Several platforms report an empty uuids list during discovery and only fill it in after pairing, so treat a match as a hint and keep the full list reachable.

Not available on iOS#

iOS has no discovery API for Bluetooth Classic. startDiscovery and scan throw BtcUnsupportedException there, and getPairedDevices returns the MFi accessories your app declared. Check first:

final caps = await bluetooth.getPlatformCapabilities();
if (!caps.canDiscoverDevices) {
  // Offer the paired list instead of a scan button.
}