Xamarin : Show messages on button click

MainPage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:d="http://xamarin.com/schemas/2014/forms/design"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             mc:Ignorable="d"
             x:Class="XamarinFormsTest01.MainPage">

    <StackLayout>
        <!-- Place new controls here -->
        <Label Text="Welcome to Xamarin.Forms!" 
           HorizontalOptions="Center"
           VerticalOptions="CenterAndExpand" />
        <Button x:Name="BtnStart" Text="start" Pressed="BtnStart_Pressed" />
        <Button x:Name="BtnStop" Text="stop" />
    </StackLayout>

</ContentPage>

MainPage.xaml.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;

namespace XamarinFormsTest01
{
    // Learn more about making custom code visible in the Xamarin.Forms previewer
    // by visiting https://aka.ms/xamarinforms-previewer
    [DesignTimeVisible(false)]
    public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
        }
        private void BtnStart_Pressed(object sender, EventArgs e)
        {
            showmsg();
        }

        private async void showmsg()
        {
            var action = await DisplayActionSheet("Select an action", "OK", "CANCEL", "Action 1", "Action 2", "Action 3");
            await DisplayAlert("Alert", "action = " + action, "OK");
        }
    }

}