How to send/write and receive/read (BIDI) Bluetooth Data from Blazor

Product JSPrintManager for Blazor Published 05/21/2026 Updated 05/21/2026 Author

Overview

JSPrintManager for Blazor supports Bidirectional (BIDI) Bluetooth Communication through the RFCOMM (Radio frequency communication) protocol from Blazor allowing you to Send/Write & Receive/Read data strings to any BT Address and Channel reachable from the client system.

IMPORTANT: The target BT Address requires to be in the client's allow list!

In this walkthrough, you'll learn how to Send/Write & Receive/Read data strings from Blazor through any BT Address and Channel reachable from the client machine. This solution works with any popular browser like Chrome, Firefox, IE/Edge & Safari on Windows, Linux, Raspberry Pi, Android and Mac systems!

Follow up these steps

  • Be sure you install in your dev machine JSPrintManager (JSPM) (Available for Windows, Linux, Raspberry Pi & Mac)
    This small app must be installed on each client that will print from your website!
  • In your Blazor project...
    • Add a NuGet reference to the JSPrintManager Razor Component
    • Add the JSPrintManager service...
      • Add the following statement at the top of your Startup or Program file
        using Neodynamic.Blazor;
        • For Blazor Server
          Add the following line in the Startup's ConfigureServices method
          services.AddJSPrintManager();
          For .NET 8+ you must use Interactive Server components and render mode, so add these settings:
          
    builder.Services.AddRazorComponents()
    .AddInteractiveServerComponents();
     
          
    app.MapRazorComponents<App>()
    .AddInteractiveServerRenderMode()
        • For Blazor WebAssembly
          Add the following line in the Program's Main method
          builder.Services.AddJSPrintManager();
    • Add the following statement in the _Imports.razor file
      @using Neodynamic.Blazor
    • Add a new Razor Page and copy/paste the following code. Please read the source code comments to understand the printing logic!
      For .NET 8+ Blazor Server you must use Interactive Server render mode, so add these settings:
      
@page "/"
@rendermode InteractiveServer
@inject JSPrintManager JSPrintManager

      
@page "/"
@inherits LayoutComponentBase
@inject JSPrintManager JSPrintManager

@using System
@using System.Text

<div>
    <strong>JSPM </strong><span>WebSocket Status </span>

    @if (JSPrintManager.Status == JSPMWSStatus.Open)
    {
        <span class="badge badge-success">
            <i class="fa fa-check" /> Open
        </span>
    }
    else if (JSPrintManager.Status == JSPMWSStatus.Closed)
    {
        <span class="badge badge-danger">
            <i class="fa fa-exclamation-circle" /> Closed!
        </span>
        <div>
            <strong>JSPrintManager (JSPM) App</strong> is not installed or not running! <a href="https://neodynamic.com/downloads/jspm" target="_blank">Download JSPM Client App...</a>
        </div>
    }
    else if (JSPrintManager.Status == JSPMWSStatus.Blocked)
    {
        <span class="badge badge-warning">
            <i class="fa fa-times-circle" /> This Website is Blocked!
        </span>
    }
    else if (JSPrintManager.Status == JSPMWSStatus.WaitingForUserResponse)
    {
        <span class="badge badge-warning">
            <i class="fa fa-user-circle" /> Waiting for user response...
        </span>
    }
</div>

@if (JSPrintManager.Status == JSPMWSStatus.Open)
{
    <div class="row">
        <div class="col-md-12">
            <h2 class="text-center">
                BIDI Bluetooth Comm
            </h2>
            <hr />
        </div>
    </div>


    <div class="row">
        <div class="col-md-12">
            <EditForm Model="@MyBtComm">
                <div class="form-group">
                    <div class="row">
                        <div class="col-md-6">
                            <label>Address:</label>
                            <InputText @bind-Value="MyBtComm.Address" class="form-control form-control-sm" placeholder="00.00.00.00.00.00" />
                        </div>
                        <div class="col-md-2">
                            <label>Channel:</label>
                            <InputNumber @bind-Value="MyBtComm.Channel" class="form-control form-control-sm" />
                        </div>
                        <div class="col-md-2">
                            <button class="btn btn-primary" @onclick="OpenPopup">Show BT Devices...</button>
                        </div>
                    </div>
                    <br /><br />
                    <div class="row">
                        <div class="col-md-2">
                            <button class="btn btn-success btn-lg" @onclick="DoBtBidi">
                                Start BIDI Comm...
                            </button>
                        </div>
                        <div class="col-md-2">
                            <button class="btn btn-danger btn-lg" @onclick="StopBtBidi">
                                Stop
                            </button>
                        </div>
                    </div>
                    <br /><br />
                    <div class="row">
                        <div class="col-md-12">
                            <br />
                            <strong>Data to Send:</strong>
                            <div class="input-group mb-3">
                                <InputText @bind-Value="dataToSend" class="form-control form-control-sm" />
                                <div class="input-group-append">
                                    <button class="btn btn-info" @onclick="DoSendData">
                                        Send...
                                    </button>
                                </div>
                            </div>
                        </div>
                    </div>
                    <br /><br />
                    <div class="row">
                        <div class="col-md-12">
                            <div class="text-center">
                                BT Comm BIDI Messages<br />
                                <textarea class="terminal" readOnly @bind="Messages" rows="10" cols="100" />
                            </div>
                        </div>
                    </div>
                </div>
            </EditForm>
        </div>
    </div>


}

@if (IsVisible)
{
    <div class="modal fade show" style="display:block; background-color: rgba(0,0,0,0.5);" tabindex="-1">
        <div class="modal-dialog">
            <div class="modal-content">

                <div class="modal-header">
                    <h5 class="modal-title">Available BT Devices</h5>
                    <button type="button" class="btn-close" @onclick="ClosePopup" aria-label="Close"></button>
                </div>

                <div class="modal-body">
                    <p>@BtDevicesInfo</p>
                </div>

                <div class="modal-footer">
                    <button type="button" class="btn btn-secondary" @onclick="ClosePopup">Close</button>
                </div>

            </div>
        </div>
    </div>
}

@code {

    protected override void OnAfterRender(bool firstRender)
    {
        if (firstRender)
        {

            // Handle OnGetBluetoothDevices event...
            JSPrintManager.OnGetBluetoothDevices += () =>
            {
                var sb = new StringBuilder();
                foreach (var btDev in JSPrintManager.BluetoothDevices)
                {
                    sb.Append($"Name: {btDev.Name}\n DeviceAddress: {btDev.Address}\n----------------------");
                }
                BtDevicesInfo = sb.ToString();

                StateHasChanged();
            };

            JSPrintManager.OnStatusChanged += () =>
            {
                StateHasChanged();

                // Status = Open means that JSPM Client App is up and running!
                if (JSPrintManager.Status == JSPMWSStatus.Open)
                {
                    //Try getting BT devices...
                    JSPrintManager.TryGetBluetoothDevices();
                }
            };


            // Start WebSocket comm
            JSPrintManager.Start();
        }

        base.OnAfterRender(firstRender);
    }

    protected override void OnInitialized()
    {
        JSPrintManager.OnError += () =>
        {
            var error = JSPrintManager.LastErrorMessage;
        };

        base.OnInitialized();
    }



    private string Messages
    {
        get
        {
            return MessagesBuffer.ToString();
        }
        set
        {
            MessagesBuffer.Clear();
            MessagesBuffer.Append(value);
        }
    }

    private string BtDevicesInfo = "No BT Devices found.";

    private StringBuilder MessagesBuffer = new StringBuilder();
    private string dataToSend;

    // The BTComm info obj
    private BTComm MyBtComm { get; set; } = new();

    private void DoBtBidi()
    {
        // handle BT Comm messages
        JSPrintManager.OnBTCommEvent += () =>
        {
            var evt = JSPrintManager.BTCommEventCache[JSPrintManager.BTCommEventCache.Count - 1];

            switch (evt.Type)
            {
                case BTCommEventType.Close:
                    MessagesBuffer.Append("COMM CLOSE" + Environment.NewLine);
                    break;
                case BTCommEventType.Error:
                    MessagesBuffer.Append("COMM ERROR: " + evt.Data + Environment.NewLine);
                    break;
                case BTCommEventType.Open:
                    MessagesBuffer.Append("COMM OPEN" + Environment.NewLine);
                    break;
                case BTCommEventType.DataReceived:
                    MessagesBuffer.Append("<< " + evt.Data);
                    break;
                case BTCommEventType.DataSent:
                    MessagesBuffer.Append(">> " + evt.Data);
                    break;
            }

            StateHasChanged();

        };

        // Start BIDI BT Comm...
        JSPrintManager.OpenBTComm(MyBtComm);

    }

    private void StopBtBidi()
    {
        // Stop BIDI BT Comm...
        JSPrintManager.CloseBTComm(MyBtComm);
    }

    private void DoSendData()
    {
        // Send data through BIDI BT Comm...
        if (string.IsNullOrWhiteSpace(dataToSend) == false)
        {
            MyBtComm.DataToSend = dataToSend;
            JSPrintManager.SendDataBTComm(MyBtComm);
        }

    }

    private bool IsVisible { get; set; } = false;

    private void OpenPopup()
    {
        IsVisible = true;
    }

    private void ClosePopup()
    {
        IsVisible = false;
    }
}
  • That's it! Run your website and play with it.


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