public class MainActivity : Activity

{

    TextView _dateDisplay;

    Button _dateSelectButton;

    protected override void OnCreate(Bundle bundle)

    {

        base.OnCreate(bundle);

        SetContentView(Resource.Layout.Main);

        _dateDisplay = FindViewById<TextView>(Resource.Id.date_display);

        _dateSelectButton = FindViewById<Button>(Resource.Id.date_select_button);

        _dateSelectButton.Click += DateSelect_OnClick;

    }

    void DateSelect_OnClick(object sender, EventArgs eventArgs)

    {

        DatePickerFragment frag = DatePickerFragment.NewInstance(delegate (DateTime time)

        {

            _dateDisplay.Text = time.ToLongDateString();

        });

        frag.Show(FragmentManager, DatePickerFragment.TAG);

    }

}

public class DatePickerFragment : DialogFragment, DatePickerDialog.IOnDateSetListener

{

    // TAG can be any string of your choice.

    public static readonly string TAG = "X:" + typeof(DatePickerFragment).Name.ToUpper();

    // Initialize this value to prevent NullReferenceExceptions.

    Action<DateTime> _dateSelectedHandler = delegate { };

    public static DatePickerFragment NewInstance(Action<DateTime> onDateSelected)

    {

        DatePickerFragment frag = new DatePickerFragment();

        frag._dateSelectedHandler = onDateSelected;

        return frag;

    }

    public override Dialog OnCreateDialog(Bundle savedInstanceState)

    {

        DateTime currently = DateTime.Now;

        DatePickerDialog dialog = new DatePickerDialog(Activity,

                                                       this,

                                                       currently.Year,

                                                       currently.Month - ,

                                                       currently.Day);

        return dialog;

    }

    public void OnDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth)

    {

        // Note: monthOfYear is a value between 0 and 11, not 1 and 12!

        DateTime selectedDate = new DateTime(year, monthOfYear + , dayOfMonth);

        Log.Debug(TAG, selectedDate.ToLongDateString());

        _dateSelectedHandler(selectedDate);

    }

}

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:padding="@dimen/top_padding">

    <TextView

        android:id="@+id/date_display"

        android:layout_height="wrap_content"

        android:layout_width="match_parent"

        android:paddingTop="@dimen/top_padding"

        android:text="@string/selected_date_text"

        style="@android:style/TextAppearance.Large" />

    <Button

        android:id="@+id/date_select_button"

        android:paddingLeft="@dimen/left_padding"

        android:paddingRight="@dimen/right_padding"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:text="@string/pick_date_text"

        android:layout_below="@id/date_display" />

</RelativeLayout>