FlutterBluePlus is sponsored by Jamcorder.

Note: this plugin is continuous work from FlutterBlue.

Migrating from FlutterBlue? See Migration Guide

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

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, or bluetooth_low_energy.

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

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.

FlutterBluePlus supports nearly every feature on all supported platforms: iOS, macOS, Android.

FlutterBluePlus has zero dependencies besides Flutter, Android, iOS, and macOS themselves.

This makes FlutterBluePlus very stable, and easy to maintain.

Use flutter_blue_plus_windows if you need Windows support.

It is maintained by @chan150.

Linux & Web support are not planned for FlutterBluePlus.

If you would like to implement flutter_blue_plus_linux, or flutter_blue_plus_web, please do!

Please star this repo & on pub.dev. We all benefit from having a larger community.

There is a community Discord server. (Link)

FlutterBluePlus has a beautiful example app, useful to debug issues.

cd ./example
flutter run

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.

// if your terminal doesn't support color you'll see annoying logs like `\x1B[1;35m`
FlutterBluePlus.setLogLevel(LogLevel.verbose, color:false);

// optional
FlutterBluePlus.logs.listen((String s){
    // send logs anywhere you want
});

Setting LogLevel.verbose shows all data in and out.

⚫ = function name

🟣 = args to platform

🟡 = data from platform

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();

If your device is not found, see Common Problems.

Note: It is recommended to set scan filters to reduce main thread & platform channel usage.

// listen to scan results
// Note: `onScanResults` clears the results between scans. You should use
//  `scanResults` if you want the current scan results *or* the results from the 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()` as an alternative to timeout
await FlutterBluePlus.startScan(
  withServices:[Guid("180D")], // match any of the specified services
  withNames:["Bluno"], // *or* any of the specified names
  timeout: Duration(seconds:15));

// wait for scanning to stop
await FlutterBluePlus.isScanning.where((val) => val == false).first;

// 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.disconnectReason?.code} ${device.disconnectReason?.description}");
    }
});

// cleanup: cancel subscription when disconnected
//   - [delayed] This option is only meant for `connectionState` subscriptions.  
//     When `true`, we cancel after a small delay. This ensures the `connectionState` 
//     listener receives the `disconnected` event.
//   - [next] if true, the the stream will be canceled only on the *next* disconnection,
//     not the current disconnection. This is useful if you setup your subscriptions
//     before you connect.
device.cancelWhenDisconnected(subscription, delayed:true, next:true);

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

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

// cancel to prevent duplicate listeners
subscription.cancel();

Connects whenever your device is found.

// enable auto connect
//  - note: autoConnect is incompatible with mtu argument, so you must call requestMtu yourself
await device.connect(autoConnect:true, mtu:null)

// wait until connection
//  - when using autoConnect, connect() always returns immediately, so we must
//    explicity listen to `device.connectionState` to know when connection occurs 
await device.connectionState.where((val) => val == BluetoothConnectionState.connected).first;

// disable auto connect
await device.disconnect()

To save a device between app restarts, just write the remoteId to a file.

Now you can connect without needing to scan again, like so:

final String remoteId = await File('/remoteId.txt').readAsString();
var device = BluetoothDevice.fromId(remoteId);
// AutoConnect is convenient because it does not "time out"
// even if the device is not available / turned off.
await device.connect(autoConnect: true);

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);
}

// Note: You must call discoverServices after every re-connection!
List<BluetoothService> services = await device.discoverServices();
services.forEach((service) {
    // do something with service
});

// Reads all characteristics
var characteristics = service.characteristics;
for(BluetoothCharacteristic c in characteristics) {
    if (c.properties.read) {
        List<int> value = await c.read();
        print(value);
    }
}

// Writes to a characteristic
await c.write([0x12, 0x34]);

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);

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 = min(device.mtuNow - 3, 512); // 3 bytes BLE overhead, 512 bytes max
    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);
    }
  }
}

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);

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);

// 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])

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();
});

Get devices currently connected to your app.

List<BluetoothDevice> devs = FlutterBluePlus.connectedDevices;
for (var d in devs) {
    print(d);
}

Get devices connected to the system by any app.

Note: before you can communicate, you must connect your app to these devices

// `withServices` required on iOS, ignored on android
List<Guid> withServices = [Guid("180F")]; 
List<BluetoothDevice> devs = await FlutterBluePlus.systemDevices(withServices);
for (var d in devs) {
    await d.connect(); // Must connect *our* app to the device
    await d.discoverServices();
}

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();

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}');
}

To mock FlutterBluePlus for development, refer to the Mocking Guide.

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

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" />

If you want to use Bluetooth to determine location, or support iBeacons.

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" />

And set androidUsesFineLocation when scanning:

// Start scanning
flutterBlue.startScan(timeout: Duration(seconds: 4), androidUsesFineLocation: true);

Add the following line in your project/android/app/proguard-rules.pro file:

-keep class com.lib.flutter_blue_plus.* { *; }

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

In the ios/Runner/Info.plist let’s add:

<dict>
    <key>NSBluetoothAlwaysUsageDescription</key>
    <string>This app needs Bluetooth to function</string>

For location permissions on iOS see more at: https://developer.apple.com/documentation/corelocation/requesting_authorization_for_location_services

Make sure you have granted access to the Bluetooth hardware:

Xcode -> Runners -> Targets -> Runner-> Signing & Capabilities -> App Sandbox -> Hardware -> Enable Bluetooth

This is an advanced use case. FlutterBluePlus does not support everything. You may have to fork it. PRs are welcome.

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>

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.

To wake up your app even after it is killed by the OS, set the restoreState option to true before starting any FBP work**:

FlutterBluePlus.setOptions(restoreState: true);

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.

You can try using https://pub.dev/packages/flutter_foreground_task or possibly https://pub.dev/packages/workmanager

🌀 = Stream ⚡ = synchronous

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

then in pubspec.yaml add the repo by path:

  flutter_blue_plus:
    path: /user/downloads/flutter_blue_plus

Now you can edit the FlutterBluePlus code yourself.

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
• iBeacons not showing

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 ...)

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.

For iOS:

adapterState always starts as unknown. You need to wait longer for the service to initialize. As simple as:

if (await FlutterBluePlus.adapterState.first == BluetoothAdapterState.unknown) {
    await Future.delayed(const Duration(seconds: 1));
}

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.

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()

1. you're using an emulator

Use a physical device.

2. 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?

3. 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.

4. 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
    }
}

5. your scan filters are wrong.

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

6. Android: you're calling startScan too often

On Adroid you can only call startScan 5 times per 30 second period. This is a platform restriction.

7. Android: make sure location services are enabled

Android requires location services to allow bluetooth scanning.

This is expected.

You must set the removeIfGone scan option if you want the device to go away when no longer available.

iOS:

iOS does not support iBeacons using CoreBluetooth. You must find a plugin meant for CoreLocation.

Android:

1. you need to enable location permissions, see Getting Started
2. you must pass androidUsesFineLocation:true to the startScan method.

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.

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()

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

You can google this error. It is a common iOS ble error code.

It means your device stopped working. FlutterBluePlus cannot fix it.

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.

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

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.

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.

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.

1. you are not calling the right function

lastValueStream will receive data for chr.read() & chr.write() & chr.setNotifyValue(true)

onValueReceived will receive data for chr.read() & chr.setNotifyValue(true)

2. your device has nothing to send

If you are using 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

Verify that the mtu is large enough to hold your message.

device.mtu

If it still happens, it is a problem with your peripheral device.

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);

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.

This is a bug in android itself.

You can call createBond() yourself just after connecting and this will resolve the issue.

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.