如何在扩展Application Xamarin.Forms的类中添加Xamarin.Forms.Init（）

Question

我试图在扩展应用程序的类中添加Xamarin.Forms.Init()，但它在下面给出了一个错误：

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.InvalidOperationException: You MUST call Xamarin.Forms.Init(); prior to using it.
  at Xamarin.Forms.Device.get_PlatformServices () [0x00007] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Core\Device.cs:79
  at Xamarin.Forms.Device.GetAssemblies () [0x00000] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Core\Device.cs:161
  at Xamarin.Forms.DependencyService.Initialize () [0x00008] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Core\DependencyService.cs:72
  at Xamarin.Forms.DependencyService.Get[T] (Xamarin.Forms.DependencyFetchTarget fetchTarget) [0x00000] in C:\BuildAgent3\work\ca3766cfc22354a1\Xamarin.Forms.Core\DependencyService.cs:18
  at Diabetes.localDB.MedicationDatabase..ctor () [0x00008] in /Users/haleem/Projects/Diabetes/Diabetes/localDB/MedicationDatabase.cs:15
  at Diabetes.Droid.MainApplication..ctor (System.IntPtr handle, Android.Runtime.JniHandleOwnership transer) [0x00000] in /Users/haleem/Projects/Diabetes/Droid/MainApplication.cs:27
  at at (wrapper managed-to-native) System.Reflection.MonoCMethod:InternalInvoke (System.Reflection.MonoCMethod,object,object[],System.Exception&)
  at System.Reflection.MonoCMethod.InternalInvoke (System.Object obj, System.Object[] parameters) [0x00002] in <896ad1d315ca4ba7b117efb8dacaedcf>:0
  --- End of inner exception stack trace ---

现在正在寻找添加Xamarin.Forms.Init()的方法，以下是我的代码：

public class MainApplication : Application
    {
        ISetAlarm alarmService;
        MedicationDatabase db = new MedicationDatabase();

        public MainApplication()
        {

        }
        public MainApplication(IntPtr handle, JniHandleOwnership transer) : base(handle, transer)
        {
        }




        public override void OnCreate()
        {

            base.OnCreate();
            //global::Xamarin.Forms.Forms.Init(this);
            Xamarin.Forms.Init();
            alarmService = new SetAlarmImplementation();
            var alarm_list = db.GetAlarmList();
            //Debug.WriteLine(" Time -- : "+ m.ToString());
            var message = "Hello Its I remind you to take insulin";
            var title = "Diabetics App";
            foreach (var list in alarm_list)
            {
                var hour = Int32.Parse(list.Substring(0, 2));
                var minute = Int32.Parse(list.Substring(3, 2));
                alarmService.SetAlarm(hour, minute, title, message);
                // Create your application here
            }
        }


    }

如何将其添加到那里请在应用程序

中使用