CODEWITHSUNDEEP
c#uwpbluetoothbluetooth-lowenergybluetooth-gatt
Specker
Specker

Reputation: 11

Write to Bluetooth LE Characteristic as a Server in WPF or UWP

I want to write into a Bluetooth LE Characteristic. (wpf c#, but has to work with UWP also)

I'm not exactly sure how this works, because I want to write a value not as a client, but as the server. Like in the MS Example:

https://github.com/microsoft/Windows-universal-samples/blob/main/Samples/BluetoothLE/cs/Scenario3_ServerForeground.xaml.cs

The BLE service and characteristic are created on program start. (not in the MS example, but in my program)

After creating a Characteristic

GattLocalCharacteristicResult result = await serviceProvider.Service.CreateCharacteristicAsync(Constants.ModeCharacteristicUuid, Constants.modeParameters);
       
modeCharacteristic = result.Characteristic;
       
modeCharacteristic.WriteRequested += ModeCharacteristic_WriteRequestedAsync;

I want to use this method to write into the characteristic:

private async void ModeCharacteristic_WriteRequestedAsync(GattLocalCharacteristic sender, GattWriteRequestedEventArgs args)
    {
        using (args.GetDeferral())
        {
            
            GattWriteRequest request = await args.GetRequestAsync();
            if (request == null)
            {
                // No access allowed to the device.  Application should indicate this to the user.
                return;
            }
           
            request.Respond();

        }
    }

Only question to me now is how to write in the Mode-Characteristic.

For example, I simply want to write a 5 into this Characteristic. What code do I need?

ModeCharacteristic_WriteRequestedAsync(modeCharacteristic, 5);

doesn't work.

I don't know how to use GattWriteRequestedEventArgs args or the event handler.

Upvotes: 0

Views: 1149

Answers (2)

Specker
Specker

Reputation: 11

This is the code I'm now using. It works exactly like it should. First create a characteristic, then adding a subscribedClientsChanged eventhandler.

GattLocalCharacteristicResult result = await serviceProvider.Service.CreateCharacteristicAsync(Constants.ModusCharacteristicUuid, Constants.gattOperandParameters);
        if (result.Error == BluetoothError.Success)
        {
            modeCharacteristic = result.Characteristic;
        }
        else
        {
            return false;
        }
        
modeCharacteristic.SubscribedClientsChanged += ResultCharacteristic_SubscribedClientsChanged;

private void ResultCharacteristic_SubscribedClientsChanged(GattLocalCharacteristic sender, object args)
    {
        ModeNotify(5);
    }

private async void ModeNotify(int computedValue)
    {
        var writer = new DataWriter();
        writer.ByteOrder = ByteOrder.LittleEndian;
        writer.WriteInt32(computedValue);

        IReadOnlyList<GattClientNotificationResult> results = await modeCharacteristic.NotifyValueAsync(writer.DetachBuffer());

    }

Upvotes: 1

CoCaIceDew
CoCaIceDew

Reputation: 248

Write to Bluetooth LE Characteristic as a Server in WPF or UWP

You should process write operation in GattLocalCharacteristic ReadRequested, when the client send read request, you can get GattReadRequest in above event, and then call RespondWithValue to response data that written with data writer.

private async void ResultCharacteristic_ReadRequestedAsync(GattLocalCharacteristic sender, GattReadRequestedEventArgs args)
{
    // BT_Code: Process a read request. 
    using (args.GetDeferral())
    {
        // Get the request information.  This requires device access before an app can access the device's request. 
        GattReadRequest request = await args.GetRequestAsync();
        if (request == null)
        {
            // No access allowed to the device.  Application should indicate this to the user.
            rootPage.NotifyUser("Access to device not allowed", NotifyType.ErrorMessage);
            return;
        }

        var writer = new DataWriter();
        writer.ByteOrder = ByteOrder.LittleEndian;
        writer.WriteInt32(resultVal);

        // Can get details about the request such as the size and offset, as well as monitor the state to see if it has been completed/cancelled externally.
        // request.Offset
        // request.Length
        // request.State
        // request.StateChanged += <Handler>

        // Gatt code to handle the response
        request.RespondWithValue(writer.DetachBuffer());
    }
}

Upvotes: 1

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