Xamarin android bluetooth le

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Bluetooth LE plugin for Xamarin

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baskren/xamarin-bluetooth-le

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README.md

Bluetooth LE plugin for Xamarin

Xamarin and MvvMCross plugin for accessing the bluetooth functionality. The plugin is loosely based on the BLE implementation of Monkey Robotics.

Important Note: With the term «vanilla» we mean the non MvvmCross/pure Xamarin version. You can use it without MvvmCross, if you download the vanilla package.

Platform	Version	Limitations
Xamarin.Android	4.3
Xamarin.iOS	7.0
Xamarin.Mac	10.9 (Mavericks)	>= v2.1.0
UWP	1709 — 10.0.16299 (Fall Creators Update)	TBA

// stable Install-Package Plugin.BLE // or pre-release Install-Package Plugin.BLE -Pre 

Install-Package MvvmCross.Plugin.BLE // or Install-Package MvvmCross.Plugin.BLE -Pre 

Add these permissions to AndroidManifest.xml. For Marshmallow and above, please follow Requesting Runtime Permissions in Android Marshmallow and don’t forget to prompt the user for the location permission.

uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" /> uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> uses-permission android:name="android.permission.BLUETOOTH" /> uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />

Android 12 and above may require one or more of the following additional runtime permissions, depending on which features of the library you are using (see the android Bluetooth permissions documentation)

uses-permission android:name="android.permission.BLUETOOTH_SCAN" /> uses-permission android:name="android.permission.BLUETOOTH_CONNECT" /> uses-permission android:name="android.permission.BLUETOOTH_ADVERTISE" />

Add this line to your manifest if you want to declare that your app is available to BLE-capable devices only:

uses-feature android:name="android.hardware.bluetooth_le" android:required="true"/>

On iOS you must add the following keys to your Info.plist

UIBackgroundModes  bluetooth-central bluetooth-peripheral  NSBluetoothPeripheralUsageDescription YOUR CUSTOM MESSAGE NSBluetoothAlwaysUsageDescription YOUR CUSTOM MESSAGE 

On MacOS (version 11 and above) you must add the following keys to your Info.plist :

 NSBluetoothAlwaysUsageDescription YOUR CUSTOM MESSAGE 

We provide a sample Xamarin.Forms app, that is a basic bluetooth LE scanner. With this app, it’s possible to

• check the ble status
• discover devices
• connect/disconnect
• discover the services
• discover the characteristics
• see characteristic details
• read/write and register for notifications of a characteristic

Have a look at the code and use it as starting point to learn about the plugin and play around with it.

var ble = CrossBluetoothLE.Current; var adapter = CrossBluetoothLE.Current.Adapter;

The MvvmCross plugin registers IBluetoothLE and IAdapter as lazy initialized singletons. You can resolve/inject them as any other MvvmCross service. You don’t have to resolve/inject both. It depends on your use case.

var ble = Mvx.ResolveIBluetoothLE>(); var adapter = Mvx.ResolveIAdapter>();

MyViewModel(IBluetoothLE ble, IAdapter adapter)  this.ble = ble; this.adapter = adapter; >

Please make sure you have this code in your LinkerPleaseLink.cs file

public void Include(MvvmCross.Plugins.BLE.iOS.Plugin plugin)  plugin.Load(); >

You can also listen for State changes. So you can react if the user turns on/off bluetooth on you smartphone.

ble.StateChanged += (s, e) =>  Debug.WriteLine($"The bluetooth state changed to e.NewState>"); >;

adapter.DeviceDiscovered += (s,a) => deviceList.Add(a.Device); await adapter.StartScanningForDevicesAsync();

var scanFilterOptions = new ScanFilterOptions(); scanFilterOptions.ServiceUuids = new [] guid1, guid2, etc>; // cross platform filter scanFilterOptions.ManufacturerIds = new [] 1,2,3,etc>; // android only filter scanFilterOptions.DeviceAddresses = new [] "80:6F:B0:43:8D:3B","80:6F:B0:25:C3:15",etc>; // android only filter await adapter.StartScanningForDevicesAsync(scanFilterOptions);

Set adapter.ScanTimeout to specify the maximum duration of the scan.

Set adapter.ScanMode to specify scan mode. It must be set before calling StartScanningForDevicesAsync() . Changing it while scanning, will not affect the current scan.

ConnectToDeviceAsync returns a Task that finishes if the device has been connected successful. Otherwise a DeviceConnectionException gets thrown.

try  await _adapter.ConnectToDeviceAsync(device); > catch(DeviceConnectionException e)  // . could not connect to device >

ConnectToKnownDeviceAsync can connect to a device with a given GUID. This means that if the device GUID is known, no scan is necessary to connect to a device. This can be very useful for a fast background reconnect. Always use a cancellation token with this method.

• On iOS it will attempt to connect indefinitely, even if out of range, so the only way to cancel it is with the token.
• On Android this will throw a GATT ERROR in a couple of seconds if the device is out of range.

try  await _adapter.ConnectToKnownDeviceAsync(guid, cancellationToken); > catch(DeviceConnectionException e)  // . could not connect to device >

var services = await connectedDevice.GetServicesAsync();

or get a specific service:

var service = await connectedDevice.GetServiceAsync(Guid.Parse("ffe0ecd2-3d16-4f8d-90de-e89e7fc396a5"));

var characteristics = await service.GetCharacteristicsAsync();

or get a specific characteristic:

var characteristic = await service.GetCharacteristicAsync(Guid.Parse("d8de624e-140f-4a22-8594-e2216b84a5f2"));

var bytes = await characteristic.ReadAsync();

await characteristic.WriteAsync(bytes);

characteristic.ValueUpdated += (o, args) =>  var bytes = args.Characteristic.Value; >; await characteristic.StartUpdatesAsync();

var descriptors = await characteristic.GetDescriptorsAsync();

var bytes = await descriptor.ReadAsync();

await descriptor.WriteAsync(bytes);

Returns all BLE devices connected or bonded (only Android) to the system. In order to use the device in the app you have to first call ConnectAsync.

• For iOS the implementation uses get retrieveConnectedPeripherals(services)
• For Android this function merges the functionality of thw following API calls:
  • getConnectedDevices
  • getBondedDevices()

  var systemDevices = adapter.GetSystemConnectedOrPairedDevices(); foreach(var device in systemDevices)  await _adapter.ConnectToDeviceAsync(device); >

  Caution! Important remarks / API limitations

  The BLE API implementation (especially on Android) has the following limitations:

  • Characteristic/Descriptor Write: make sure you call characteristic.WriteAsync(. ) from the main thread, failing to do so will most probably result in a GattWriteError.
  • Sequential calls: Always wait for the previous BLE command to finish before invoking the next. The Android API needs it’s calls to be serial, otherwise calls that do not wait for the previous ones will fail with some type of GattError. A more explicit example: if you call this in your view lifecycle (onAppearing etc) all these methods return void and 100% don’t quarantee that any await bleCommand() called here will be truly awaited by other lifecycle methods.
  • Scan wit services filter: On specifically Android 4.3 the scan services filter does not work (due to the underlying android implementation). For android 4.3 you will have to use a workaround and scan without a filter and then manually filter by using the advertisement data (which contains the published service GUIDs).
  • Surround Async API calls in try-catch blocks. Most BLE calls can/will throw an exception in certain cases, this is especially true for Android. We will try to update the xml doc to reflect this.

  try  await _adapter.ConnectToDeviceAsync(device); > catch(DeviceConnectionException ex)  //specific > catch(Exception ex)  //generic >

  • Avoid caching of Characteristic or Service instances between connection sessions. This includes saving a reference to them in you class between connection sessions etc. After a device has been disconnected all Service & Characteristic instances become invalid. Allways use GetServiceAsync and GetCharacteristicAsync to get a valid instance.
  • Scanning: Avoid performing ble device operations like Connect, Read, Write etc while scanning for devices. Scanning is battery-intensive.
    • try to stop scanning before performing device operations (connect/read/write/etc)
    • try to stop scanning as soon as you find the desired device
    • never scan on a loop, and set a time limit on your scan

    How to build the nuget package

    1. Build Open a console, change to the folder «xamarin-bluetooth-le/.build» and run cake .
    2. pack the nuget nuget pack Plugin.BLE.nuspec nuget pack MvvmCross.Plugin.BLE.nuspec

    We usually do our development work on a branch with the name of the milestone. So please base your pull requests on the currently open development branch.

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