ble.net is a cross-platform Bluetooth Low Energy (aka BLE, aka Bluetooth LE, aka Bluetooth Smart) library to enable simple development of BLE clients on Android, iOS, and UWP/Windows.
It provides a consistent API across all supported platforms and hides most of the problems and poor API decisions of the native BLE APIs.
| Platform | Version |
|---|---|
| Xamarin.iOS | iOS 8.3+ |
| Xamarin.Android | API 18+ |
| Windows 10 (UWP) | 1709+ |
Note: Currently UWP only supports listening for broadcasts/advertisements, not connecting to devices.
This is a quick overview of the API and usage; continue reading below for setup instructions and more comprehensive examples.
var connection = await ble.FindAndConnectToDevice(
new ScanFilter().AddAdvertisedService( service ),
TimeSpan.FromSeconds( 30 )
);
if(connection.IsSuccessful())
{
try
{
var gattServer = connection.GattServer;
var read = gattServer.ReadCharacteristicValue( service, char1 );
await Task.WhenAll( new Task[]
{
gattServer.WriteCharacteristicValue(
service, char1, new Byte[]{/* bytes */}
),
gattServer.WriteCharacteristicValue(
service, char2, new Byte[]{/* bytes */}
),
gattServer.WriteCharacteristicValue(
service2, char3, new Byte[]{/* bytes */}
)
} );
// Even though we await "read" after awaiting the write calls, the read was
// dispatched first and so will have executed prior to the write calls
originalValue = await read;
}
catch(GattException ex)
{
Debug.WriteLine( ex.ToString() );
}
finally
{
// The device will stay connected until you call Disconnect or the connection is lost through some external means.
await connection.GattServer.Disconnect();
}
}Install the ble.net (API) package.
dotnet add package ble.netNOTE: BLE.net switched from targetting
portable-net45+win8in version1.1.1, to.netstandard1.4in version1.2.0, to.netstandard2.0in1.2.1(where it will remain for the forseeable future). If you are having problems please file an issue
Install the relevant platform package. (See table at the top of the readme for supported versions.)
dotnet add package ble.net-androiddotnet add package ble.net-iosdotnet add package ble.net-uwp[assembly: UsesPermission( Manifest.Permission.Bluetooth )]
[assembly: UsesPermission( Manifest.Permission.BluetoothAdmin )]If you are having issues discovering devices when scanning, try adding coarse location permissions. Android has inconsistent behavior across devices and adding this permission sometimes helps.
[assembly: UsesPermission( Manifest.Permission.AccessCoarseLocation )]Note also that this is a "dangerous" permission in API 23+, so if you are targeting Android 6.0 or higher you will need to request this permission from the user at runtime.
If you are only using BLE in the foreground, when your app is active, you don't need to do any further setup for iOS.
If you need to use BLE in the background:
- Add bluetooth-central to background modes
- Add a string value for key NSBluetoothPeripheralUsageDescription. iOS will display this value in a permission dialog box that the user must approve.
<!-- Info.plist -->
<key>UIBackgroundModes</key>
<array>
<string>bluetooth-central</string>
</array>
<key>NSBluetoothPeripheralUsageDescription</key>
<string>[MyAppNameHere] would like to use bluetooth.</string><!-- Package.appxmanifest -->
<Capabilities>
<DeviceCapability Name="bluetooth" />
</Capabilities>There is no initialization needed for iOS or UWP.
If you want IBluetoothLowEnergyAdapter.DisableAdapter() and IBluetoothLowEnergyAdapter.EnableAdapter() to work, then in your main Activity add:
protected override void OnCreate( Bundle bundle )
{
// ...
BluetoothLowEnergyAdapter.Init( this );
// ...
}If you want IBluetoothLowEnergyAdapter.CurrentState.Subscribe() to work, then in your calling Activity add:
protected sealed override void OnActivityResult( Int32 requestCode, Result resultCode, Intent data )
{
BluetoothLowEnergyAdapter.OnActivityResult( requestCode, resultCode, data );
}Each platform project has a static method BluetoothLowEnergyAdapter.ObtainDefaultAdapter() which you call from your platform project and provide to your application code using whatever strategy you prefer (dependency injection, manual reference passing, a singleton or service locator, etc).
See the sample Xamarin Forms app for real-life examples:
- Android Xamarin.Forms example
- iOS Xamarin.Forms example
- UWP Xamarin.Forms example
See sample Xamarin Forms app included in the repo for further examples of how to integrate BLE.net into an app.
All the examples presume you have obtained the IBluetoothLowEnergyAdapter as per the setup notes above, e.g.:
IBluetoothLowEnergyAdapter ble = /* platform-provided adapter from BluetoothLowEnergyAdapter.ObtainDefaultAdapter()*/;There are corresponding methods to disable the adapter.
if(ble.AdapterCanBeEnabled && ble.CurrentState.IsDisabledOrDisabling()) {
await ble.EnableAdapter();
}ble.CurrentState.Value; // e.g.: EnabledDisabledState.Enabled
// The adapter implements IObservable<EnabledDisabledState> so you can subscribe to its state
ble.CurrentState.Subscribe( state => Debug.WriteLine("New State: {0}", state) );var cts = new CancellationTokenSource(TimeSpan.FromSeconds( 30 ));
await ble.ScanForBroadcasts(
// providing ScanSettings is optional
new ScanSettings()
{
// Setting the scan mode is currently only applicable to Android and has no effect on other platforms.
// If not provided, defaults to ScanMode.Balanced
Mode = ScanMode.LowPower,
// Optional scan filter to ensure that the observer will only receive peripherals
// that pass the filter. If you want to scan for everything around, omit the filter.
Filter = new ScanFilter()
{
AdvertisedDeviceName = "foobar",
AdvertisedManufacturerCompanyId = 76,
// peripherals must advertise at-least-one of any GUIDs in this list
AdvertisedServiceIsInList = new List<Guid>(){ someGuid },
},
// ignore repeated advertisements from the same device during this scan
IgnoreRepeatBroadcasts = false
},
// Your IObserver<IBlePeripheral> or Action<IBlePeripheral> will be triggered for each discovered
// peripheral based on the provided scan settings and filter (if any).
( IBlePeripheral peripheral ) =>
{
// read the advertising data
var adv = peripheral.Advertisement;
Debug.WriteLine( adv.DeviceName );
Debug.WriteLine( adv.Services.Select( x => x.ToString() ).Join( "," ) );
Debug.WriteLine( adv.ManufacturerSpecificData.FirstOrDefault().CompanyName() );
Debug.WriteLine( adv.ServiceData );
// if we found what we needed, stop the scan manually
cts.Cancel();
// perhaps connect to the device (see next example)...
},
// Provide a CancellationToken to stop the scan, or use the overload that takes a TimeSpan.
// If you omit this argument, the scan will timeout after BluetoothLowEnergyUtils.DefaultScanTimeout
cts.Token
);
// scanning has stopped when code reached this point since the scan was awaitedYou can also create a ScanFilter using a fluent builder syntax if you prefer that:
new ScanFilter()
.SetAdvertisedDeviceName( "foobar" )
.SetAdvertisedManufacturerCompanyId( 76 )
.AddAdvertisedService( someGuid )If you have already scanned for and discovered a peripheral and you now want to connect to it:
var connection = await ble.ConnectToDevice(
// The IBlePeripheral to connect to
peripheral,
// TimeSpan or CancellationToken to stop the
// connection attempt.
// If you omit this argument, it will use
// BluetoothLowEnergyUtils.DefaultConnectionTimeout
TimeSpan.FromSeconds( 15 ),
// Optional IProgress<ConnectionProgress>
progress => Debug.WriteLine(progress)
);
if(connection.IsSuccessful())
{
var gattServer = connection.GattServer;
// ... do things with gattServer here... (see later examples...)
}
else
{
// Do something to inform user or otherwise handle unsuccessful connection.
Debug.WriteLine( "Error connecting to device. result={0:g}", connection.ConnectionResult );
// e.g., "Error connecting to device. result=ConnectionAttemptCancelled"
}Be sure to disconnect when you are done:
await gattServer.Disconnect();In use-cases where you are not scanning for advertisements but rather looking to connect to a specific, known, device:
var connection = await ble.FindAndConnectToDevice(
new ScanFilter()
.SetAdvertisedDeviceName( "foo" )
.SetAdvertisedManufacturerCompanyId( 0xffff )
.AddAdvertisedService( guid ),
TimeSpan.FromSeconds( 30 ) );
if(connection.IsSuccessful())
{
// ...
}Debug.WriteLine(gattServer.State); // e.g. ConnectionState.Connected
// the server implements IObservable<ConnectionState> so you can subscribe to its state
gattServer.Subscribe( state =>
{
if(state == ConnectionState.Disconnected)
{
Debug.WriteLine("Connection Lost");
}
} );You can provide information for the GUIDs representing services, characteristics, and descriptors with KnownAttributes.
var known = new KnownAttributes();
// You can add descriptions for any desired
// characteristics, services, and descriptors
known.AddService( myGuid1, "Foo" );
known.AddCharacteristic( myGuid2, "Bar" );
known.AddDescriptor( myGuid3, "Baz" );There are shortcuts to add all the attributes that have been adopted by the Bluetooth SIG.
known.AddAdoptedServices();
known.AddAdoptedCharacteristics();
known.AddAdoptedDescriptors();You can also create a new KnownAttributes with all the above adopted attributes already populated:
known = KnownAttributes.CreateWithAdoptedAttributes();Then use it as a lookup as needed.
known.Get(guid);
known.GetDescriptionOrGuid(guid);foreach(var guid in await gattServer.ListAllServices())
{
Debug.WriteLine( $"service: {known.GetDescriptionOrGuid(guid)}" );
}Debug.WriteLine( $"service: {serviceGuid}" );
foreach(var guid in await gattServer.ListServiceCharacteristics( serviceGuid ))
{
Debug.WriteLine( $"characteristic: {known.GetDescriptionOrGuid(guid)}" );
}try
{
var value = await gattServer.ReadCharacteristicValue( someServiceGuid, someCharacteristicGuid );
}
catch(GattException ex)
{
Debug.WriteLine( ex.ToString() );
}IDisposable notifyHandler;
try
{
// Will also stop listening when gattServer
// is disconnected, so if that is acceptable,
// you don't need to store this disposable.
notifyHandler = gattServer.NotifyCharacteristicValue(
someServiceGuid,
someCharacteristicGuid,
// IObserver<Tuple<Guid, Byte[]>> or IObserver<Byte[]> or
// Action<Tuple<Guid, Byte[]>> or Action<Byte[]>
bytes => {/* do something with notification bytes */} );
}
catch(GattException ex)
{
Debug.WriteLine( ex.ToString() );
}
// ... later, once done listening for notifications ...
notifyHandler.Dispose();try
{
// The resulting value of the characteristic is returned. In nearly all cases this
// will be the same value that was provided to the write call (e.g. `byte[]{ 1, 2, 3 }`)
var value = await gattServer.WriteCharacteristicValue(
someServiceGuid,
someCharacteristicGuid,
new byte[]{ 1, 2, 3 } );
}
catch(GattException ex)
{
Debug.WriteLine( ex.ToString() );
}BLE.net uses a simple logging library internally. You can add a log "sink" to receive each log entry which you can then write to the console or a logging system of your choice.
Also, each platform's static
BluetoothLowEnergyAdapter.ObtainAdapter()method has an overload that takes anILog. If no log is provided the default log (SystemLog.Instance) is used, but you could provide your own entire logging implementation if you really wanted to.
var logId = Assembly.GetAssembly( GetType() ).GetName().Name;
// ble.net will log to SystemLog.Instance unless provided a custom logger
SystemLog.Instance.AddSink(
entry =>
{
var message = entry.FormatAsString();
switch(entry.Severity)
{
case LogLevel.Error:
Log.Error( logId, message );
break;
case LogLevel.Warn:
Log.Warn( logId, message );
break;
case LogLevel.Info:
Log.Info( logId, message );
break;
case LogLevel.Trace:
default:
Log.Debug( logId, message );
break;
}
} );// ble.net will log to SystemLog.Instance unless provided a custom logger
SystemLog.Instance.AddSink(
entry =>
{
var message = entry.FormatAsString();
if(entry.Severity == LogLevel.Error)
{
Console.Error.WriteLine( message );
}
else
{
Console.Out.WriteLine( message );
}
} );