flutter_blue_plus_harmony

Description:

flutter blue plus harmony

Note: this plugin is continuous work from FlutterBlue.
Migrating from FlutterBlue? See Migration Guide
Contents #

Introduction
Usage
Getting Started
Using Ble in App Background
Reference
Debugging
Mocking
Common Problems

Introduction #
FlutterBluePlus is a Bluetooth Low Energy plugin for Flutter.
It supports BLE Central Role only (most common).
If you need BLE Peripheral Role, you should check out FlutterBlePeripheral.
Tutorial #
If you are new to Bluetooth, you should start by reading BLE tutorials.

Novel Bits BLE Tutorial
All About Circuits BLE Tutorial
Embetronicx BLE Tutorial

❗ Bluetooth Classic is not supported ❗ #
i.e. Arduino HC-05 & HC-06, speakers, headphones, mice, keyboards, gamepads, and more are not supported. These all use Bluetooth Classic.
Also, iBeacons are not supported on iOS. Apple requires you to use CoreLocation.
Cross-Platform Bluetooth Low Energy #
FlutterBluePlus supports nearly every feature on all supported platforms: iOS, macOS, Android.
FlutterBluePlus was written to be simple, robust, and easy to understand.
No Dependencies #
FlutterBluePlus has zero dependencies besides Flutter, Android, and iOS themselves.
This makes FlutterBluePlus very stable, and easy to maintain.
⭐ Stars ⭐ #
Please star this repo & on pub.dev. We all benefit from having a larger community.
Discord 💬 #
There is a community Discord server. (Link)
Example #
FlutterBluePlus has a beautiful example app, useful to debug issues.
cd ./example
flutter run
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Usage #
🔥 Error Handling 🔥 #
Flutter Blue Plus takes error handling seriously.
Every error returned by the native platform is checked and thrown as an exception where appropriate. See Reference for a list of throwable functions.
Streams: Streams returned by FlutterBluePlus never emit any errors and never close. There's no need to handle onError or onDone for stream.listen(...). The one exception is FlutterBluePlus.scanResults, which you should handle onError.

Set Log Level #
// if your terminal doesn't support color you'll see annoying logs like `\x1B[1;35m`
FlutterBluePlus.setLogLevel(LogLevel.verbose, color:false)
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Setting LogLevel.verbose shows all data in and out.
⚫ = function name
🟣 = args to platform
🟡 = data from platform

Bluetooth On & Off #
Note: On iOS, a "This app would like to use Bluetooth" system dialogue appears on first call to any FlutterBluePlus method.
// first, check if bluetooth is supported by your hardware
// Note: The platform is initialized on the first call to any FlutterBluePlus method.
if (await FlutterBluePlus.isSupported == false) {
print("Bluetooth not supported by this device");
return;
}

// handle bluetooth on & off
// note: for iOS the initial state is typically BluetoothAdapterState.unknown
// note: if you have permissions issues you will get stuck at BluetoothAdapterState.unauthorized
var subscription = FlutterBluePlus.adapterState.listen((BluetoothAdapterState state) {
print(state);
if (state == BluetoothAdapterState.on) {
// usually start scanning, connecting, etc
} else {
// show an error to the user, etc
}
});

// turn on bluetooth ourself if we can
// for iOS, the user controls bluetooth enable/disable
if (Platform.isAndroid) {
await FlutterBluePlus.turnOn();
}

// cancel to prevent duplicate listeners
subscription.cancel();
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Scan for devices #
If your device is not found, see Common Problems.
Note: It is recommended to set scan filters to reduce main thread & platform channel usage.
Note: scan filters use an "or" behavior. i.e. if you set withServices & withNames we return all the advertisments that match any of the specified services or any of the specified names.
// listen to scan results
// Note: `onScanResults` only returns live scan results, i.e. during scanning
// Use: `scanResults` if you want live scan results *or* the results from a previous scan
var subscription = FlutterBluePlus.onScanResults.listen((results) {
if (results.isNotEmpty) {
ScanResult r = results.last; // the most recently found device
print('${r.device.remoteId}: "${r.advertisementData.advName}" found!');
}
},
onError: (e) => print(e),
);

// cleanup: cancel subscription when scanning stops
FlutterBluePlus.cancelWhenScanComplete(subscription);

// Wait for Bluetooth enabled & permission granted
// In your real app you should use `FlutterBluePlus.adapterState.listen` to handle all states
await FlutterBluePlus.adapterState.where((val) => val == BluetoothAdapterState.on).first;

// Start scanning w/ timeout
// optional: use `stopScan()` to stop the scan at anytime
await FlutterBluePlus.startScan(withServices:[Guid("180D")], timeout: Duration(seconds:15));

// wait for scanning to stop
await FlutterBluePlus.isScanning.where((val) => val == false).first;
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Connect to a device #
// listen for disconnection
var subscription = device.connectionState.listen((BluetoothConnectionState state) async {
if (state == BluetoothConnectionState.disconnected) {
// 1. typically, start a periodic timer that tries to
// reconnect, or just call connect() again right now
// 2. you must always re-discover services after disconnection!
print("${device.disconnectReasonCode} ${device.disconnectReasonDescription}");
}
});

// Connect to the device
await device.connect();

// Disconnect from device
await device.disconnect();

// cancel to prevent duplicate listeners
subscription.cancel();
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Auto Connect #
Connects whenever your device is found.
// enable auto connect
// - this function always returns immediately
// - you must listen to `device.connectionState` to know when connection occurs
// - autoConnect is incompatible with mtu argument, so you must call requestMtu yourself
await device.connect(mtu:null, autoConnect:true)

// disable auto connect
await device.disconnect()
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MTU #
On Android, we request an mtu of 512 by default during connection (see: connect function arguments).
On iOS & macOS, the mtu is negotiated automatically, typically 135 to 255.
final subscription = device.mtu.listen((int mtu) {
// iOS: initial value is always 23, but iOS will quickly negotiate a higher value
print("mtu $mtu");
});

// cleanup: cancel subscription when disconnected
device.cancelWhenDisconnected(subscription);

// You can also manually change the mtu yourself.
if (Platform.isAndroid) {
await device.requestMtu(512);
}
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Discover services #
// Note: You must call discoverServices after every re-connection!
List<BluetoothService> services = await device.discoverServices();
services.forEach((service) {
// do something with service
});
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Read Characteristics #
// Reads all characteristics
var characteristics = service.characteristics;
for(BluetoothCharacteristic c in characteristics) {
if (c.properties.read) {
List<int> value = await c.read();
print(value);
}
}
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Write Characteristic #
// Writes to a characteristic
await c.write([0x12, 0x34]);
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allowLongWrite: To write large characteristics (up to 512 bytes) regardless of mtu, use allowLongWrite:
/// allowLongWrite should be used with caution.
/// 1. it can only be used *with* response to avoid data loss
/// 2. the peripheral device must support the 'long write' ble protocol.
/// 3. Interrupted transfers can leave the characteristic in a partially written state
/// 4. If the mtu is small, it is very very slow.
await c.write(data, allowLongWrite:true);
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splitWrite: To write lots of data (unlimited), you can define the splitWrite function.
import 'dart:math';
// split write should be used with caution.
// 1. due to splitting, `characteristic.read()` will return partial data.
// 2. it can only be used *with* response to avoid data loss
// 3. The characteristic must be designed to support split data
extension splitWrite on BluetoothCharacteristic {
Future<void> splitWrite(List<int> value, {int timeout = 15}) async {
int chunk = device.mtuNow - 3; // 3 bytes ble overhead
for (int i = 0; i < value.length; i += chunk) {
List<int> subvalue = value.sublist(i, min(i + chunk, value.length));
await write(subvalue, withoutResponse:false, timeout: timeout);
}
}
}
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Subscribe to a characteristic #
If onValueReceived is never called, see Common Problems in the README.
final subscription = characteristic.onValueReceived.listen((value) {
// onValueReceived is updated:
// - anytime read() is called
// - anytime a notification arrives (if subscribed)
});

// cleanup: cancel subscription when disconnected
device.cancelWhenDisconnected(subscription);

// subscribe
// Note: If a characteristic supports both **notifications** and **indications**,
// it will default to **notifications**. This matches how CoreBluetooth works on iOS.
await characteristic.setNotifyValue(true);
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Last Value Stream #
lastValueStream is an alternative to onValueReceived. It emits a value any time the characteristic changes, including writes.
It is very convenient for simple characteristics that support both WRITE and READ (and/or NOTIFY). e.g. a "light switch toggle" characteristic.
final subscription = characteristic.lastValueStream.listen((value) {
// lastValueStream` is updated:
// - anytime read() is called
// - anytime write() is called
// - anytime a notification arrives (if subscribed)
// - also when first listened to, it re-emits the last value for convenience.
});

// cleanup: cancel subscription when disconnected
device.cancelWhenDisconnected(subscription);

// enable notifications
await characteristic.setNotifyValue(true);
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Read and write descriptors #
// Reads all descriptors
var descriptors = characteristic.descriptors;
for(BluetoothDescriptor d in descriptors) {
List<int> value = await d.read();
print(value);
}

// Writes to a descriptor
await d.write([0x12, 0x34])
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Services Changed Characteristic #
FlutterBluePlus automatically listens to the Services Changed Characteristic (0x2A05)
In FlutterBluePlus, we call it onServicesReset because you must re-discover services.
// - uses the GAP Services Changed characteristic (0x2A05)
// - you must call discoverServices() again
device.onServicesReset.listen(() async {
print("Services Reset");
await device.discoverServices();
});
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Get Connected Devices #
Get devices currently connected to your app.
List<BluetoothDevice> devs = FlutterBluePlus.connectedDevices;
for (var d in devs) {
print(d);
}
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Get System Devices #
Get devices connected to the system by any app.
Note: you must connect your app to them before you can communicate with them.
List<BluetoothDevice> devs = await FlutterBluePlus.systemDevices;
for (var d in devs) {
await d.connect(); // Must connect *our* app to the device
await d.discoverServices();
}
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Create Bond (Android Only) #
Note: calling this is usually not necessary!! The platform will do it automatically.
However, you can force the popup to show sooner.
final bsSubscription = device.bondState.listen((value) {
print("$value prev:{$device.prevBondState}");
});

// cleanup: cancel subscription when disconnected
device.cancelWhenDisconnected(bsSubscription);

// Force the bonding popup to show now (Android Only)
await device.createBond();

// remove bond
await device.removeBond();
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Events API #
Access streams from all devices simultaneously.
There are streams for:

events.onConnectionStateChanged
events.onMtuChanged
events.onReadRssi
events.onServicesReset
events.onDiscoveredServices
events.onCharacteristicReceived
events.onCharacteristicWritten
events.onDescriptorRead
events.onDescriptorWritten
events.onNameChanged (iOS Only)
events.onBondStateChanged (Android Only)

// listen to *any device* connection state changes
FlutterBluePlus.events.onConnectionStateChanged.listen((event)) {
print('${event.device} ${event.connectionState}');
}
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Mocking #
To mock FlutterBluePlus for development, refer to the Mocking Guide.
Getting Started #
Change the minSdkVersion for Android #
flutter_blue_plus is compatible only from version 21 of Android SDK so you should change this in android/app/build.gradle:
Android {
defaultConfig {
minSdkVersion: 21
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Add permissions for Android (No Location) #
In the android/app/src/main/AndroidManifest.xml add:
<!-- Tell Google Play Store that your app uses Bluetooth LE
Set android:required="true" if bluetooth is necessary -->
<uses-feature android:name="android.hardware.bluetooth_le" android:required="false" />

<!-- New Bluetooth permissions in Android 12
https://developer.android.com/about/versions/12/features/bluetooth-permissions -->
<uses-permission android:name="android.permission.BLUETOOTH_SCAN" android:usesPermissionFlags="neverForLocation" />
<uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />

<!-- legacy for Android 11 or lower -->
<uses-permission android:name="android.permission.BLUETOOTH" android:maxSdkVersion="30" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" android:maxSdkVersion="30" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" android:maxSdkVersion="30"/>

<!-- legacy for Android 9 or lower -->
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" android:maxSdkVersion="28" />
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Add permissions for Android (With Fine Location) #
If you want to use Bluetooth to determine location.
In the android/app/src/main/AndroidManifest.xml add:
<!-- Tell Google Play Store that your app uses Bluetooth LE
Set android:required="true" if bluetooth is necessary -->
<uses-feature android:name="android.hardware.bluetooth_le" android:required="false" />

<!-- New Bluetooth permissions in Android 12
https://developer.android.com/about/versions/12/features/bluetooth-permissions -->
<uses-permission android:name="android.permission.BLUETOOTH_SCAN"/>
<uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

<!-- legacy for Android 11 or lower -->
<uses-permission android:name="android.permission.BLUETOOTH" android:maxSdkVersion="30" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" android:maxSdkVersion="30" />

<!-- legacy for Android 9 or lower -->
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" android:maxSdkVersion="28" />
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And set androidUsesFineLocation when scanning:
// Start scanning
flutterBlue.startScan(timeout: Duration(seconds: 4), androidUsesFineLocation: true);
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Android Proguard #
Add the following line in your project/android/app/proguard-rules.pro file:
-keep class com.lib.flutter_blue_plus.* { *; }
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to avoid seeing the following kind errors in your release builds:
PlatformException(startScan, Field androidScanMode_ for m0.e0 not found. Known fields are
[private int m0.e0.q, private b3.b0$i m0.e0.r, private boolean m0.e0.s, private static final m0.e0 m0.e0.t,
private static volatile b3.a1 m0.e0.u], java.lang.RuntimeException: Field androidScanMode_ for m0.e0 not found
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Add permissions for iOS #
In the ios/Runner/Info.plist let’s add:
<dict>
<key>NSBluetoothAlwaysUsageDescription</key>
<string>This app always needs Bluetooth to function</string>
<key>NSBluetoothPeripheralUsageDescription</key>
<string>This app needs Bluetooth Peripheral to function</string>
<key>NSLocationAlwaysAndWhenInUseUsageDescription</key>
<string>This app always needs location and when in use to function</string>
<key>NSLocationAlwaysUsageDescription</key>
<string>This app always needs location to function</string>
<key>NSLocationWhenInUseUsageDescription</key>
<string>This app needs location when in use to function</string>
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For location permissions on iOS see more at: https://developer.apple.com/documentation/corelocation/requesting_authorization_for_location_services
And in Xcode, add access to Bluetooth hardware:
Xcode -> Runners -> Targets -> Runner-> Signing & Capabilities -> App Sandbox -> Hardware -> Enable Bluetooth

Using Ble in App Background #
This is an advanced use case. FlutterBluePlus does not support everything. You may have to fork it. PRs are welcome.
iOS #
Documentation: https://developer.apple.com/library/archive/documentation/NetworkingInternetWeb/Conceptual/CoreBluetooth_concepts/CoreBluetoothBackgroundProcessingForIOSApps/PerformingTasksWhileYourAppIsInTheBackground.html
Add the following to your Info.plist
<key>UIBackgroundModes</key>
<array>
<string>bluetooth-central</string>
</array>
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When this key-value pair is included in the app’s Info.plist file, the system wakes up your app to process ble read, write, and subscription events.
You may also have to use https://pub.dev/packages/flutter_isolate
Note: Upon being woken up, an app has around 10 seconds to complete a task. Apps that spend too much time executing in the background can be throttled back by the system or killed.
Android #
You can try using https://pub.dev/packages/flutter_foreground_task or possibly https://pub.dev/packages/flutter_isolate
Reference #
🌀 = Stream
⚡ = synchronous
FlutterBluePlus API #




Android
iOS
Throws
Description




setLogLevel
✅
✅

Configure plugin log level


isSupported
✅
✅

Checks whether the device supports Bluetooth


turnOn
✅

🔥
Turns on the bluetooth adapter


adapterStateNow ⚡
✅
✅

Current state of the bluetooth adapter


adapterState 🌀
✅
✅

Stream of on & off states of the bluetooth adapter


startScan
✅
✅
🔥
Starts a scan for Ble devices


stopScan
✅
✅
🔥
Stop an existing scan for Ble devices


onScanResults 🌀
✅
✅

Stream of live scan results


scanResults 🌀
✅
✅

Stream of live scan results or previous results


lastScanResults ⚡
✅
✅

The most recent scan results


isScanning 🌀
✅
✅

Stream of current scanning state


isScanningNow ⚡
✅
✅

Is a scan currently running?


connectedDevices ⚡
✅
✅

List of devices connected to your app


systemDevices
✅
✅
🔥
List of devices connected to the system, even by other apps


getPhySupport
✅

🔥
Get supported bluetooth phy codings



FlutterBluePlus Events API #




Android
iOS
Throws
Description




events.onConnectionStateChanged 🌀
✅
✅

Stream of connection changes of all devices


events.onMtuChanged 🌀
✅
✅

Stream of mtu changes of all devices


events.onReadRssi 🌀
✅
✅

Stream of rssi reads of all devices


events.onServicesReset 🌀
✅
✅

Stream of services resets of all devices


events.onDiscoveredServices 🌀
✅
✅

Stream of services discovered of all devices


events.onCharacteristicReceived 🌀
✅
✅

Stream of characteristic value reads of all devices


events.onCharacteristicWritten 🌀
✅
✅

Stream of characteristic value writes of all devices


events.onDescriptorRead 🌀
✅
✅

Stream of descriptor value reads of all devices


events.onDescriptorWritten 🌀
✅
✅

Stream of descriptor value writes of all devices


events.onBondStateChanged 🌀
✅


Stream of android bond state changes of all devices


events.onNameChanged 🌀

✅

Stream of iOS name changes of all devices



BluetoothDevice API #




Android
iOS
Throws
Description




platformName ⚡
✅
✅

The platform preferred name of the device


advName ⚡
✅
✅

The advertised name of the device found during scanning


connect
✅
✅
🔥
Establishes a connection to the device


disconnect
✅
✅
🔥
Cancels an active or pending connection to the device


isConnected ⚡
✅
✅

Is this device currently connected to your app?


connectionState 🌀
✅
✅

Stream of connection changes for the Bluetooth Device


discoverServices
✅
✅
🔥
Discover services


servicesList ⚡
✅
✅

The current list of available services


onServicesReset 🌀
✅
✅

The services changed & must be rediscovered


mtu 🌀
✅
✅

Stream of current mtu value + changes


mtuNow ⚡
✅
✅

The current mtu value


readRssi
✅
✅
🔥
Read RSSI from a connected device


requestMtu
✅

🔥
Request to change the MTU for the device


requestConnectionPriority
✅

🔥
Request to update a high priority, low latency connection


bondState 🌀
✅


Stream of device bond state. Can be useful on Android


createBond
✅

🔥
Force a system pairing dialogue to show, if needed


removeBond
✅

🔥
Remove Bluetooth Bond of device


setPreferredPhy
✅

🔥
Set preferred RX and TX phy for connection and phy options


clearGattCache
✅

🔥
Clear android cache of service discovery results



BluetoothCharacteristic API #




Android
iOS
Throws
Description




uuid ⚡
✅
✅

The uuid of characteristic


read
✅
✅
🔥
Retrieves the value of the characteristic


write
✅
✅
🔥
Writes the value of the characteristic


setNotifyValue
✅
✅
🔥
Sets notifications or indications on the characteristic


isNotifying ⚡
✅
✅

Are notifications or indications currently enabled


onValueReceived 🌀
✅
✅

Stream of characteristic value updates received from the device


lastValue ⚡
✅
✅

The most recent value of the characteristic


lastValueStream 🌀
✅
✅

Stream of onValueReceived + writes



BluetoothDescriptor API #




Android
iOS
Throws
Description




uuid ⚡
✅
✅

The uuid of descriptor


read
✅
✅
🔥
Retrieves the value of the descriptor


write
✅
✅
🔥
Writes the value of the descriptor


onValueReceived 🌀
✅
✅

Stream of descriptor value reads & writes


lastValue ⚡
✅
✅

The most recent value of the descriptor


lastValueStream 🌀
✅
✅

Stream of onValueReceived + writes



Debugging #
The easiest way to debug issues in FlutterBluePlus is to make your own local copy.
cd /user/downloads
git clone https://github.com/boskokg/flutter_blue_plus.git
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then in pubspec.yaml add the repo by path:
flutter_blue_plus:
path: /user/downloads/flutter_blue_plus
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Now you can edit the FlutterBluePlus code yourself.
Common Problems #
Many common problems are easily solved.
Adapter:

bluetooth must be turned on
adapterState is not 'on' but my Bluetooth is on
adapterState is called multiple times

Scanning:

Scanning does not find my device
Scanned device never goes away

Connecting:

Connection fails
connectionState is called multiple times
remoteId is different on Android vs iOS
iOS: "[Error] The connection has timed out unexpectedly."

Reading & Writing:

List of Bluetooth GATT Errors
Characteristic write fails
Characteristic read fails

Subscriptions:

onValueReceived is never called (or lastValueStream)
onValueReceived data is split up (or lastValueStream)
onValueReceived is called with duplicate data (or lastValueStream)

Android Errors:

ANDROID_SPECIFIC_ERROR
android pairing popup appears twice

Flutter Errors:

MissingPluginException(No implementation found for method XXXX ...)


"bluetooth must be turned on" #
You need to wait for the bluetooth adapter to fully turn on.
await FlutterBluePlus.adapterState.where((state) => state == BluetoothAdapterState.on).first;
You can also use FlutterBluePlus.adapterState.listen(...). See Usage.

adapterState is not 'on' but my Bluetooth is on #
For iOS:
adapterState always starts as unknown. You need to wait longer for the service to initialize. Use this code:
// wait for actual adapter state, up to 3 seconds
Set<BluetoothAdapterState> inProgress = {BluetoothAdapterState.unknown, BluetoothAdapterState.turningOn};
var adapterState = FlutterBluePlus.adapterState.where((v) => !inProgress.contains(v)).first;
await adapterState.timeout(const Duration(seconds: 3)).onError((error, stackTrace) {
throw Exception("Could not determine Bluetooth state. ${FlutterBluePlus.adapterStateNow}");
});

// check adapter state
if (FlutterBluePlus.adapterStateNow != BluetoothAdapterState.on) {
throw Exception("Bluetooth Is Not On. ${FlutterBluePlus.adapterStateNow}");
}
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If adapterState is unavailable, you must add access to Bluetooth Hardware in the app's Xcode settings. See Getting Started.
For Android:
Check that your device supports Bluetooth & has permissions.

adapterState is called multiple times #
You are forgetting to cancel the original FlutterBluePlus.adapterState.listen resulting in multiple listeners.
// tip: using ??= makes it easy to only make new listener when currently null
final subscription ??= FlutterBluePlus.adapterState.listen((value) {
// ...
});

// also, make sure you cancel the subscription when done!
subscription.cancel()
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Scanning does not find my device #
1. try using another ble scanner app

iOS: nRF Connect
Android: BLE Scanner

Install a BLE scanner app on your phone. Can it find your device?
2. your device uses bluetooth classic, not BLE.
Headphones, speakers, keyboards, mice, gamepads, & printers all use Bluetooth Classic.
These devices may be found in System Settings, but they cannot be connected to by FlutterBluePlus. FlutterBluePlus only supports Bluetooth Low Energy.
3. your device stopped advertising.

you might need to reboot your device
you might need to put your device in "discovery mode"
your phone may have already connected automatically
another app may have already connected to your device
another phone may have already connected to your device

Try looking through system devices:
// search system devices. i.e. any device connected to by *any* app
List<BluetoothDevice> system = await FlutterBluePlus.systemDevices;
for (var d in system) {
print('${r.device.platformName} already connected to! ${r.device.remoteId}');
if (d.platformName == "myBleDevice") {
await r.connect(); // must connect our app
}
}
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4. your scan filters are wrong.

try removing all scan filters
for withServices to work, your device must actively advertise the serviceUUIDs it supports


Scanned device never goes away #
This is expected.
You must set the removeIfGone scan option if you want the device to go away when no longer available.

Connection fails #
1. Your ble device may be low battery
Bluetooth can become erratic when your peripheral device is low on battery.
2. Your ble device may have refused the connection or have a bug
Connection is a two-way process. Your ble device may be misconfigured.
3. You may be on the edge of the Bluetooth range.
The signal is too weak, or there are a lot of devices causing radio interference.
4. Some phones have an issue connecting while scanning.
The Huawei P8 Lite is one of the reported phones to have this issue. Try stopping your scanner before connecting.
5. Try restarting your phone
Bluetooth is a complicated system service, and can enter a bad state.

connectionState is called multiple times #
You are forgetting to cancel the original device.connectionState.listen resulting in multiple listeners.
// tip: using ??= makes it easy to only make new listener when currently null
final subscription ??= FlutterBluePlus.device.connectionState.listen((value) {
// ...
});

// also, make sure you cancel the subscription when done!
subscription.cancel()
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The remoteId is different on Android versus iOS & macOS #
This is expected. There is no way to avoid it.
For privacy, iOS & macOS use a randomly generated uuid. This uuid will periodically change.
e.g. 6920a902-ba0e-4a13-a35f-6bc91161c517
Android uses the mac address of the bluetooth device. It never changes.
e.g. 05:A4:22:31:F7:ED

iOS: "[Error] The connection has timed out unexpectedly." #
You can google this error. It is a common iOS ble error code.
It means your device stopped working. FlutterBluePlus cannot fix it.

List of Bluetooth GATT Errors #
These GATT error codes are part of the BLE Specification.
These are responses from your ble device because you are sending an invalid request.
FlutterBluePlus cannot fix these errors. You are doing something wrong & your device is responding with an error.
GATT errors as they appear on iOS:
apple-code: 1 | The handle is invalid.
apple-code: 2 | Reading is not permitted.
apple-code: 3 | Writing is not permitted.
apple-code: 4 | The command is invalid.
apple-code: 6 | The request is not supported.
apple-code: 7 | The offset is invalid.
apple-code: 8 | Authorization is insufficient.
apple-code: 9 | The prepare queue is full.
apple-code: 10 | The attribute could not be found.
apple-code: 11 | The attribute is not long.
apple-code: 12 | The encryption key size is insufficient.
apple-code: 13 | The value's length is invalid.
apple-code: 14 | Unlikely error.
apple-code: 15 | Encryption is insufficient.
apple-code: 16 | The group type is unsupported.
apple-code: 17 | Resources are insufficient.
apple-code: 18 | Unknown ATT error.
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GATT errors as they appear on Android:
android-code: 1 | GATT_INVALID_HANDLE
android-code: 2 | GATT_READ_NOT_PERMITTED
android-code: 3 | GATT_WRITE_NOT_PERMITTED
android-code: 4 | GATT_INVALID_PDU
android-code: 5 | GATT_INSUFFICIENT_AUTHENTICATION
android-code: 6 | GATT_REQUEST_NOT_SUPPORTED
android-code: 7 | GATT_INVALID_OFFSET
android-code: 8 | GATT_INSUFFICIENT_AUTHORIZATION
android-code: 9 | GATT_PREPARE_QUEUE_FULL
android-code: 10 | GATT_ATTR_NOT_FOUND
android-code: 11 | GATT_ATTR_NOT_LONG
android-code: 12 | GATT_INSUFFICIENT_KEY_SIZE
android-code: 13 | GATT_INVALID_ATTRIBUTE_LENGTH
android-code: 14 | GATT_UNLIKELY
android-code: 15 | GATT_INSUFFICIENT_ENCRYPTION
android-code: 16 | GATT_UNSUPPORTED_GROUP
android-code: 17 | GATT_INSUFFICIENT_RESOURCES
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Descriptions:
1 | Invalid Handle | The attribute handle given was not valid on this server.
2 | Read Not Permitted | The attribute cannot be read.
3 | Write Not Permitted | The attribute cannot be written.
4 | Invalid PDU | The attribute PDU was invalid.
5 | Insufficient Authentication | The attribute requires authentication before it can be read or written.
6 | Request Not Supported | Attribute server does not support the request received from the client.
7 | Invalid Offset | Offset specified was past the end of the attribute.
8 | Insufficient Authorization | The attribute requires an authorization before it can be read or written.
9 | Prepare Queue Full | Too many prepare writes have been queued.
10 | Attribute Not Found | No attribute found within the given attribute handle range.
11 | Attribute Not Long | The attribute cannot be read or written using the Read Blob or Write Blob requests.
12 | Insufficient Key Size | The Encryption Key Size used for encrypting this link is insufficient.
13 | Invalid Attribute Value Length | The attribute value length is invalid for the operation.
14 | Unlikely Error | The request has encountered an unlikely error and cannot be completed.
15 | Insufficient Encryption | The attribute requires encryption before it can be read or written.
16 | Unsupported Group Type | The attribute type is not a supported grouping as defined by a higher layer.
17 | Insufficient Resources | Insufficient Resources to complete the request.
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characteristic write fails #
First, check the List of Bluetooth GATT Errors for your error.
1. your bluetooth device turned off, or is out of range
If your device turns off or crashes during a write, it will cause a failure.
2. Your Bluetooth device has bugs
Maybe your device crashed, or is not sending a response due to software bugs.
3. there is radio interference
Bluetooth is wireless and will not always work.

Characteristic read fails #
First, check the List of Bluetooth GATT Errors for your error.
1. your bluetooth device turned off, or is out of range
If your device turns off or crashes during a read, it will cause a failure.
2. Your Bluetooth device has bugs
Maybe your device crashed, or is not sending a response due to software bugs.
3. there is radio interference
Bluetooth is wireless and will not always work.

onValueReceived is never called (or lastValueStream) #
1. you are not calling the right function
lastValueStream is called for await chr.read() & await chr.write() & await chr.setNotifyValue(true)
onValueReceived is only called for await chr.read() & await chr.setNotifyValue(true)
2. your device has nothing to send
If you are using await chr.setNotifyValue(true), your device chooses when to send data.
Try interacting with your device to get it to send new data.
3. your device has bugs
Try rebooting your ble device.
Some ble devices have buggy software and stop sending data

onValueReceived data is split up (or lastValueStream) #
Verify that the mtu is large enough to hold your message.
device.mtu
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If it still happens, it is a problem with your peripheral device.

onValueReceived is called with duplicate data (or lastValueStream) #
You are probably forgetting to cancel the original chr.onValueReceived.listen resulting in multiple listens.
The easiest solution is to use device.cancelWhenDisconnected(subscription) to cancel device subscriptions.
final subscription = chr.onValueReceived.listen((value) {
// ...
});

// make sure you have this line!
device.cancelWhenDisconnected(subscription);

await characteristic.setNotifyValue(true);
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ANDROID_SPECIFIC_ERROR #
There is no 100% solution.
FBP already has mitigations for this error, but Android will still fail with this code randomly.
The recommended solution is to catch the error, and retry.

android pairing popup appears twice #
This is a bug in android itself.
You can call createBond() yourself just after connecting and this will resolve the issue.

MissingPluginException(No implementation found for method XXXX ...) #
If you just added flutter_blue_plus to your pubspec.yaml, a hot reload / hot restart is not enough.
You need to fully stop your app and run again so that the native plugins are loaded.
Also try flutter clean.