Xamarin 无法从异步获取实例

我编写了一个通过蓝牙连接到 ESP32 的 Xamarin.Forms 应用程序。现在我想从 MainPage.xaml 页面的 CustomControl.JoystickControl 获取值。

我已经这样尝试过了：

MainPage.xaml.cs：

 public partial class MainPage : ContentPage
{

    public static Bluetooth.IBth bth = new Bluetooth.Bth();
    public MainPage()
    {
        InitializeComponent();

        Task.Run(async () => bth.Start("mecanumWheelRobot", 200, false));


    }

    public CustomControls.JoystickControl JoystickControlElement
    {
        get { return JoystickControl; }
    }
    public CustomControls.JoystickControl JoystickControlElement1
    {
        get { return JoystickControl1; }
    }
}

现在我想从以下异步函数获取 JoystickControlElement：

var mainpage = new Views.MainPage();

字符串测试 = mainpage.test;（这两行就是问题所在）

class Bth : IBth
{

    private CancellationTokenSource _ct { get; set; }
    

    const int RequestResolveError = 1000;

    public Bth()
    {
    }

    public void Start(string name, int sleepTime = 200, bool readAsCharArray = false)
    {

        Task.Run(async () => loop(name, sleepTime, readAsCharArray));
    }



    private async Task loop(string name, int sleepTime, bool readAsCharArray)
    {

        BluetoothDevice device = null;
        BluetoothAdapter adapter = BluetoothAdapter.DefaultAdapter;
        BluetoothSocket BthSocket = null;

        _ct = new CancellationTokenSource();
        while (_ct.IsCancellationRequested == false)
        {

            try
            {
                Thread.Sleep(sleepTime);

                adapter = BluetoothAdapter.DefaultAdapter;

                if (adapter == null)
                    System.Diagnostics.Debug.WriteLine("No Bluetooth adapter found.");
                else
                    System.Diagnostics.Debug.WriteLine("Adapter found!!");

                if (!adapter.IsEnabled)
                    System.Diagnostics.Debug.WriteLine("Bluetooth adapter is not enabled.");
                else
                    System.Diagnostics.Debug.WriteLine("Adapter enabled!");

                System.Diagnostics.Debug.WriteLine("Try to connect to " + name);

                foreach (var bd in adapter.BondedDevices)
                {
                    System.Diagnostics.Debug.WriteLine("Paired devices found: " + bd.Name.ToUpper());
                    if (bd.Name.ToUpper().IndexOf(name.ToUpper()) >= 0)
                    {

                        System.Diagnostics.Debug.WriteLine("Found " + bd.Name + ". Try to connect with it!");
                        device = bd;
                        break;
                    }
                }

                if (device == null)
                {
                    System.Diagnostics.Debug.WriteLine("Named device not found.");
                    MainThread.BeginInvokeOnMainThread(() =>
                    {
                        // Code to run on the main thread
                    });
                }
                else
                {
                    UUID uuid = UUID.FromString("00001101-0000-1000-8000-00805f9b34fb");
                    if ((int)Android.OS.Build.VERSION.SdkInt >= 10) // Gingerbread 2.3.3 2.3.4
                        BthSocket = device.CreateInsecureRfcommSocketToServiceRecord(uuid);
                    else
                        BthSocket = device.CreateRfcommSocketToServiceRecord(uuid);

                    if (BthSocket != null)
                    {


                        //Task.Run ((Func<Task>)loop); /*) => {
                        await BthSocket.ConnectAsync();


                        if (BthSocket.IsConnected)
                        {
                            MainThread.BeginInvokeOnMainThread(() =>
                            {
                                service.toast.toastSuccess("Connected!");
                                // Code to run on the main thread
                                //pages.bluetoothBarcodeScan.connectedScanner();
                            });
                            System.Diagnostics.Debug.WriteLine("Connected!");


                                MainThread.BeginInvokeOnMainThread(() =>
                                {
                                    service.toast.toastSuccess("Writing!");
                                    // Code to run on the main thread
                                    //
                                });
                                while (_ct.IsCancellationRequested == false)
                                {

                                    var mainpage = new Views.MainPage();
                                    string test = mainpage.test;
                                    var bytes = Encoding.ASCII.GetBytes("{test}-");
                                    BthSocket.OutputStream.Write(bytes, 0, bytes.Length);
                                    Thread.Sleep(100);

                                }

                                System.Diagnostics.Debug.WriteLine("Exit the inner loop");

                        }
                    }
                    else
                        System.Diagnostics.Debug.WriteLine("BthSocket = null");

                }


            }
            catch(Exception ex)
            {
                    service.toast.toastSuccess(ex.Message);
                }

            finally
            {
                if (BthSocket != null)
                    BthSocket.Close();
                device = null;
                adapter = null;
            }
        }

        System.Diagnostics.Debug.WriteLine("Exit the external loop");
    }
    public void Cancel()
    {
        if (_ct != null)
        {
            System.Diagnostics.Debug.WriteLine("Send a cancel to task!");
            _ct.Cancel();
            MainThread.BeginInvokeOnMainThread(() =>
            {
                service.toast.toastError("Disconnected");
                // Code to run on the main thread
            });
        }
    }

    public async Task<string> GetData()
    {
            var mainpage = new Views.MainPage();
            string test = mainpage.test;
            return "1";
    }


        public ObservableCollection<string> PairedDevices()
    {
        BluetoothAdapter adapter = BluetoothAdapter.DefaultAdapter;
        ObservableCollection<string> devices = new ObservableCollection<string>();

        foreach (var bd in adapter.BondedDevices)
            devices.Add(bd.Name);

        return devices;
    }


    #endregion
}

当涉及到这一行时，异步函数总是从新开始。

我应该如何获取变量？

您可以更改构造函数方法，例如：

  public Bth(string txt)
    {}

然后通过主页.测试 like:

public static Bluetooth.IBth bth = new Bluetooth.Bth(txt);