GATT Scenario: Control a Bluetooth LE Thermometer Device(XAML)

[This article is for Windows 8.x and Windows Phone 8.x developers writing Windows Runtime apps. If you’re developing for Windows 10, see the latest documentation]

A Windows Store App acts as a controller for a fictitious Bluetooth LE Thermometer device. The device also declares a Format characteristic which would allow a user to retrieve the value reading in either Celsius or Fahrenheit degrees, in addition to the standard characteristics of the HealthThermometer profile.

The Windows Store App uses reliable write transactions to make sure that the format and measurement interval are set as a single value.

// Uuid of the "Format" Characteristic Value
Guid formatCharacteristicUuid = 
    new Guid("{00000000-0000-0000-0000-000000000010}");

// Constant representing a Fahrenheit scale temperature measurement
const byte FahrenheitReading = 1;
async void Initialize()
{
    var themometerServices = await Windows.Devices.Enumeration
        .DeviceInformation.FindAllAsync(GattDeviceService
            .GetDeviceSelectorFromUuid(
                GattServiceUuids.HealthThermometer),
        null);

    GattDeviceService thermometerService = await
        GattDeviceService.FromIdAsync(themometerServices[0].Id);

    serviceNameTextBlock.Text = "Using service: " + 
        themometerServices[0].Name;

    GattCharacteristic intervalCharacteristic = thermometerService
        .GetCharacteristics(GattCharacteristicUuids.MeasurementInterval)[0];

    GattCharacteristic formatCharacteristic = thermometerService
        .GetCharacteristics(formatCharacteristicUuid)[0];

    GattReliableWriteTransaction gattTransaction = 
        new GattReliableWriteTransaction();

    var writer = new Windows.Storage.Streams.DataWriter();

    // Get a temperature reading every 60 seconds
    writer.WriteUInt16(60);

    gattTransaction.WriteValue(
        intervalCharacteristic, 
        writer.DetachBuffer());

    // Get the reading on the Fahrenheit scale
    writer.WriteByte(FahrenheitReading);

    gattTransaction.WriteValue(
        formatCharacteristic, 
        writer.DetachBuffer());

    GattCommunicationStatus status = await gattTransaction.CommitAsync();

    if (GattCommunicationStatus.Unreachable == status)
    {
        statusTextBlock.Text = "Writing to your device failed !";
    }
}

// Uuid of the "Format" Characteristic Value
Guid formatCharacteristicUuid(0x00000000, 0x0000, 0x0000, 0x00, 0x00, 
                                  0x00, 0x00, 0x00, 0x00, 0x00, 0x10);

// Constant representing a Fahrenheit scale temperature measurement
const unsigned char FAHRENHEIT_READING = 1;

void MainPage::Initialize()
{
    create_task(DeviceInformation::FindAllAsync(
        GattDeviceService::GetDeviceSelectorFromUuid(
            GattServiceUuids::HealthThermometer), 
        nullptr)).then(
            [this] (DeviceInformationCollection^ thermometerServices) 
    {
        create_task(GattDeviceService::FromIdAsync(
            thermometerServices->GetAt(0)->Id)).then([this] (
                GattDeviceService^ thermometerService) 
        {
            GattCharacteristic^ intervalCharacteristic = 
                thermometerService->GetCharacteristics(
                    GattCharacteristicUuids::MeasurementInterval)
                        ->GetAt(0);

            GattCharacteristic^ formatCharacteristic = 
                thermometerService->GetCharacteristics(
                    formatCharacteristicUuid)->GetAt(0);

            GattReliableWriteTransaction^ gattTransaction = 
                ref new GattReliableWriteTransaction();

            DataWriter^ writer = ref new DataWriter();

            // Get a temperature reading every 60 seconds
            writer->WriteUInt16(60);

            gattTransaction->WriteValue(
                intervalCharacteristic, 
                writer->DetachBuffer());

            writer->WriteByte(FAHRENHEIT_READING);

            gattTransaction->WriteValue(
                formatCharacteristic, 
                writer->DetachBuffer());

            create_task(gattTransaction->CommitAsync())
                .then([this] (GattCommunicationStatus status) 
            {
                if (GattCommunicationStatus::Unreachable == status) 
                { 
                    statusTextBlock->Text = 
                        ref new String(L"Writing to your device failed !");
                }
            });
        });
    });
}