手机端通过串口接收数据的代码，用Xamarin编写。

在Xamarin.Forms中处理移动端串口通信，可以利用Xamarin.Essentials库提供的`SerialDevice`类。下面是一个基本的Android示例代码，展示如何初始化、打开串口并接收数据：

using Xamarin.Essentials;
using System.Threading.Tasks;

public partial class MainPage : ContentPage
{
    private SerialDevice _serialDevice;

    public MainPage()
    {
        InitializeComponent();
        InitializeSerialPort();
    }

    async void InitializeSerialPort()
    {
        try
        {
            var devices = await Device.Info.GetSerialPortsAsync();
            if (devices.Any())
            {
                _serialDevice = new SerialDevice(devices.First());
                await _serialDevice.ConnectAsync();

                // 监听数据
                _serialDevice.DataReceived += OnSerialDataReceived;
                await Task.Run(() => _serialDevice.ReadStream.ReadLine()); // 防止阻塞UI线程
            }
            else
            {
                Console.WriteLine("No serial ports found.");
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error initializing serial port: {ex.Message}");
        }
    }

    private async void OnSerialDataReceived(object sender, SerialDataReceivedEventArgs e)
    {
        var receivedData = await _serialDevice.ReadLineAsync();
        DisplayText.Text = $"Received: {receivedData}";
    }

    protected override void OnDisappearing()
    {
        base.OnDisappearing();
        if (_serialDevice != null)
        {
            _serialDevice.DataReceived -= OnSerialDataReceived;
            _serialDevice.Dispose();
        }
    }
}

在iOS平台上，处理方式基本相似，但由于Objective-C的异步回调机制，可能会稍微复杂一些。你需要将`OnSerialDataReceived`方法添加到iOS的`UIApplicationDelegate`中，并使用GCD管理任务。