RunOnUiThread startactivity

hubProxy.On("KullaniciDogrula", (_giren_kullanici) =>
{
RunOnUiThread(() =>
{
StartActivity(typeof(MainActivity));
if (_giren_kullanici == "doğrulandı")
{
StartActivity(typeof(MainActivity));
Toast.MakeText(this, "doğrulandı" + _giren_kullanici, ToastLength.Long).Show();
}
else
{
Toast.MakeText(this, "hatalı:" + _giren_kullanici, ToastLength.Long).Show();
}
Toast.MakeText(this, "durum:" + _giren_kullanici, ToastLength.Long).Show();
});
});

I can not start an activity if the incoming character is "correct"