UWP Bluetooth RFCOMM FindAllAsync - bluetooth

Question

I want to build two simple apps, communicating with each other using Bluetooth RFCOMM.
However, when I run client app it doesn't find any devices with _devices = await DeviceInformation.FindAllAsync(RfcommDeviceService.GetDeviceSelector(RfcommServiceId.ObexObjectPush));
_devices collection is empty.
Based on the examples from microsoft docs I've managed to write something like this.
Application receiving messages (server) - deployed on Raspberry PI 3.
namespace RaspRFCOMM
{
public sealed partial class MainPage : Page
{
private RfcommServiceProvider _provider;
public MainPage()
{
this.InitializeComponent();
this.Initialize();
}
private async void Initialize()
{
msgStatus.Text = "Inicjalizacja...";
// Initialize the provider for the hosted RFCOMM service
_provider = await RfcommServiceProvider.CreateAsync(RfcommServiceId.ObexObjectPush);
// Create a listener for this service and start listening
StreamSocketListener listener = new StreamSocketListener();
listener.ConnectionReceived += OnConnectionReceived;
await listener.BindServiceNameAsync(
_provider.ServiceId.AsString(),
SocketProtectionLevel
.BluetoothEncryptionAllowNullAuthentication);
// Set the SDP attributes and start advertising
InitializeServiceSdpAttributes(_provider);
_provider.StartAdvertising(listener, true);
}
const uint SERVICE_VERSION_ATTRIBUTE_ID = 0x0300;
const byte SERVICE_VERSION_ATTRIBUTE_TYPE = 0x0A; // UINT32
const uint SERVICE_VERSION = 200;
private void InitializeServiceSdpAttributes(RfcommServiceProvider provider)
{
DataWriter writer = new DataWriter();
// First write the attribute type
writer.WriteByte(SERVICE_VERSION_ATTRIBUTE_TYPE);
// Then write the data
writer.WriteUInt32(SERVICE_VERSION);
IBuffer data = writer.DetachBuffer();
provider.SdpRawAttributes.Add(SERVICE_VERSION_ATTRIBUTE_ID, data);
}
private async void OnConnectionReceived(
StreamSocketListener listener,
StreamSocketListenerConnectionReceivedEventArgs args)
{
msgStatus.Text = "Odczytuje...";
_provider.StopAdvertising();
listener.Dispose();
StreamSocket _socket = args.Socket;
StreamReader reader = new StreamReader(_socket.InputStream.AsStreamForRead());
string response = await reader.ReadLineAsync();
msgStatus.Text = "Odczytałem...";
textboxMsg.Text = response + "To odczytalem";
}
}
}
Sending messages:
namespace WinRFCOMM
{
public sealed partial class MainPage : Page
{
private RfcommDeviceService _service;
private StreamSocket _socket;
private DeviceInformationCollection _devices;
private StreamWriter _writer;
public MainPage()
{
this.InitializeComponent();
this.Initialize();
}
private async void Initialize()
{
msgStatus.Text = "Inicjalizacja...";
_devices = await DeviceInformation.FindAllAsync(RfcommDeviceService.GetDeviceSelector(RfcommServiceId.ObexObjectPush));
this.PopulateDevicesListview(_devices);
msgStatus.Text = "Oczekiwanie na wybór...";
}
private void PopulateDevicesListview(DeviceInformationCollection devices)
{
foreach (DeviceInformation di in devices)
{
String deviceInfo = di.Name + " - " + di.Id;
lvDevices.Items.Add(deviceInfo);
}
}
private void btnConnect_Click(object sender, RoutedEventArgs e)
{
var selected = lvDevices.SelectedIndex;
if (selected != -1)
{
ConnectToRFC(_devices[selected]);
}
}
private async void ConnectToRFC(DeviceInformation selectedDevice)
{
_service = await RfcommDeviceService.FromIdAsync(selectedDevice.Id);
_socket = new StreamSocket();
await _socket.ConnectAsync(
_service.ConnectionHostName,
_service.ConnectionServiceName,
SocketProtectionLevel
.BluetoothEncryptionAllowNullAuthentication);
msgStatus.Text = "Połączono...";
_writer = new StreamWriter(_socket.OutputStream.AsStreamForWrite());
_writer.WriteLineAsync("Test");
}
}
}
Both have manifest file set up like this:
<Capabilities>
<Capability Name="internetClient" />
<Capability Name="internetClientServer" />
<Capability Name="privateNetworkClientServer" />
<DeviceCapability Name="bluetooth" />
</Capabilities>
I'd really appreciate any help, because I've been stuck for almost 2 days.

Answer 1

The problem is not reside in the code.
You need pair two devices firstly before running this RFCOMM sample. Because
Use the RfcommDeviceService.GetDeviceSelector* functions to help
generate an AQS query that can be used to enumerated paired device
instances of the desired service.
Ref: Send a file as a client

Answer 2

I found this forum post which got me through it.
My problem was trying to use the DeviceInformation I had discovered for pairing, as my point of connection for RFCOMM.
For rfcomm you will require your AppManifest to look like:
<DeviceCapability Name="bluetooth.rfcomm">
<Device Id="any">
<Function Type ="name:serialPort"/>
</Device>
</DeviceCapability>
Instead of just having the name "bluetooth".