Xamarin Forms -> System.MissingMethodException。没有找到[界面]的默认构造函数

我在Xamarin.Forms上使用依赖服务时收到了这个错误。我已经看到了关于这个错误的答案，其中涉及到iOS和链接器。然而，我是在安卓上运行的，链接器是关闭的。

构造函数告诉我，它在PCL中找不到接口的默认构造函数。

我已经搜索和调试了几个小时。有哪些事情可能导致这个错误？我非常确定我的DependencyService实现是正确的，所以我觉得这是一个不同的问题。

以下是我的相关代码。

[assembly: Xamarin.Forms.Dependency(typeof(TextRecognition))]
namespace DiabetesAPP.Droid
    [Preserve(AllMembers = true)]
    [Activity(Label = "TextRecognition", Theme = "@style/Theme.AppCompat.Light.NoActionBar", MainLauncher = true)]
    public class TextRecognition : AppCompatActivity, ISurfaceHolderCallback, IProcessor, ITextRecognition
        private SurfaceView cameraView;
        private TextView textView;
        private CameraSource cameraSource;
        public string Resultados;
        private const int RequestCameraPermissionID = 1001;
        protected override void OnCreate(Bundle savedInstanceState)
            base.OnCreate(savedInstanceState);
            SetContentView(Resource.Layout.Main);
            cameraView = FindViewById<SurfaceView>(Resource.Id.surface_view);
            textView = FindViewById<TextView>(Resource.Id.txtview);
            TextRecognizer textRecognizer = new TextRecognizer.Builder(ApplicationContext).Build();
            if (!textRecognizer.IsOperational)
                Log.Error("Main Activity", "Detector dependencies are not yet available");
                cameraSource = new CameraSource.Builder(ApplicationContext, textRecognizer)
                    .SetFacing(CameraFacing.Back)
                    .SetRequestedFps(2.0f)
                    .SetRequestedPreviewSize(1280, 1024)
                    .SetAutoFocusEnabled(true)
                    .Build();
                cameraView.Holder.AddCallback(this);
                 textRecognizer.SetProcessor(this);
            Android.Widget.Button logonButton = FindViewById<Android.Widget.Button>(Resource.Id.button_send);
            logonButton.Click += LogonButton_Click;
        public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Android.Content.PM.Permission[] grantResults)
            switch (requestCode)
                case RequestCameraPermissionID:
                        if (grantResults[0] == Android.Content.PM.Permission.Granted)
                           cameraSource.Start(cameraView.Holder);
                    break;
        public void SurfaceChanged(ISurfaceHolder holder, [GeneratedEnum] Format format, int width, int height)
        public void SurfaceCreated(ISurfaceHolder holder)
            if (ActivityCompat.CheckSelfPermission(ApplicationContext, Manifest.Permission.Camera) != Android.Content.PM.Permission.Granted)
                ActivityCompat.RequestPermissions(this, new string[]
                    Android.Manifest.Permission.Camera
                }, RequestCameraPermissionID);
                return;
           cameraSource.Start(cameraView.Holder);
        public void SurfaceDestroyed(ISurfaceHolder holder)
            cameraSource.Stop();
        public void ReceiveDetections(Detections detections)
            SparseArray items = detections.DetectedItems;
            if (items.Size() != 0)
                textView.Post(() =>
                    StringBuilder strBuilder = new StringBuilder();
                    for (int i = 0; i < items.Size(); i++)
                        strBuilder.Append(((TextBlock)items.ValueAt(i)).Value);
                        strBuilder.Append("\n");
                    textView.Text = strBuilder.ToString();
                    Resultados = strBuilder.ToString();
        private void LogonButton_Click(object sender, EventArgs e)
            //Toast.MakeText(this, "Hello from " + Resultados, ToastLength.Long).Show();
            //Intent data = new Intent(this, typeof(TextRecognition));
            //SetResult(Result.Ok, data);
            //// MessagingCenter.Send((DiabetesAPP.App)Xamarin.Forms.Application.Current, "OpenPage", "You send message:" + Resultados);
            //// MessagingCenter.Send<DiabetesAPP.App, string>(DiabetesAPP.App.Current as App, "OpenPage", "You send message:" + Resultados);
            //MessagingCenter.Send((DiabetesAPP.App)Xamarin.Forms.Application.Current, "OpenPage", "You send message:" + Resultados);
            Toast.MakeText(this, Resultados, ToastLength.Short).Show();
            MessagingCenter.Send<App, string>(App.Current as App, "OpenPage", "You send message:" + Resultados);
            Finish();
        public void Release()
        public void LaunchActivityInAndroid()
            Activity activity = Forms.Context as Activity;
            var intent = new Intent(Forms.Context, typeof(TextRecognition));
            activity.StartActivity(intent);
        protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
            base.OnActivityResult(requestCode, resultCode, data);
            switch (resultCode)
                case Result.Ok:
                    break;
            Finish();
        public interface ITextRecognition
//Update code - 16/09/2020
        public TextRecognition()
在Xamarin.Form页面中的实现
[assembly: Xamarin.Forms.Dependency(typeof(ITextRecognition))]
namespace DiabetesAPP.Views.FoodMenu
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class FoodMenu : ContentPage
        public FoodMenu()
            InitializeComponent();
        async void Food_ManualEntry(object sender, EventArgs e)
            await Navigation.PushAsync(new SearchFood());
        public void Food_CameraEntry(object sender, EventArgs e)
            Xamarin.Forms.DependencyService.Register<ITextRecognition>();
            DependencyService.Get<ITextRecognition>().LaunchActivityInAndroid();
        public interface ITextRecognition
            void LaunchActivityInAndroid();
错误。System.MissingMethodException。没有为DiabetesAPP.Views.FoodMenu.FoodMenu+ITextRecognition类型找到默认构造函数。
是什么出了问题？