OnAppearing not invoked when startup but it's ok when navigating and come back

Hi,

I have a simple app and trying ot run it on android but having a problem..

The OnAppearing is not getting invoked at all when startup.. but when I navigate from the app then come back that time it will run.. or when I keep the app active and turn of the device power (power button) and turn it on again..

What could be the reason for this?

Here is my code:

App.xaml.cs:

using System;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;
using Microsoft.AppCenter;
using Microsoft.AppCenter.Analytics;
using Microsoft.AppCenter.Crashes;

[assembly: XamlCompilation(XamlCompilationOptions.Compile)]
namespace Samana
{
    public partial class App : Application
    {
        public App()
        {    
            InitializeComponent();

            MainPage = new NavigationPage(new MainPage())
            {
                BarBackgroundColor = Color.White,
                BarTextColor = Color.Black
            };
        }

        protected override void OnStart()
        {
            // Handle when your app starts

            AppCenter.Start("android=c869509f-27c9-4f76-86a6-2b17ee3904a4; ios=948a8946-2a7a-4185-a059-892c12f50c0d", 
                typeof(Analytics), typeof(Crashes));
        }

        protected override void OnSleep()
        {
            // Handle when your app sleeps
        }

        protected override void OnResume()
        {
            // Handle when your app resumes
        }
    }
}

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:FFImageLoading="clr-namespace:FFImageLoading.Forms;assembly=FFImageLoading.Forms"
    xmlns:FFTransformations="clr-namespace:FFImageLoading.Transformations;assembly=FFImageLoading.Transformations"
    xmlns:SyncfusionBusyIndicator="clr-namespace:Syncfusion.SfBusyIndicator.XForms;assembly=Syncfusion.SfBusyIndicator.XForms"
    xmlns:local="clr-namespace:Samana"
    x:Class="Samana.MainPage">
    <Grid Padding="0" Margin="0">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>

        <Grid Grid.Row="0">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto" />
                <ColumnDefinition Width="*" />
                <ColumnDefinition Width="Auto" />
            </Grid.ColumnDefinitions>

            <Label Grid.Column="0" HorizontalOptions="Start" Text="settings" />

            <StackLayout Grid.Column="1">
                <Label x:Name="LabelPlaceName" HorizontalOptions="Center" Text="city" />
                <Label x:Name="LabelLocalTime" HorizontalOptions="Center" Text="time" />
            </StackLayout>

            <Label Grid.Column="2" HorizontalOptions="End" Text="plus" />
        </Grid>

        <Grid Grid.Row="1">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*" />
                <ColumnDefinition Width="Auto" />
            </Grid.ColumnDefinitions>

            <StackLayout Grid.Column="0" HorizontalOptions="Center" VerticalOptions="CenterAndExpand">
                <Label x:Name="LabelTemprature" HorizontalOptions="Center" FontSize="Large" />
                <Label x:Name="LabelDescription" HorizontalOptions="Center" FontSize="Medium" />
            </StackLayout>

            <FFImageLoading:CachedImage x:Name="ImageWeatherIcon" Grid.Column="1" WidthRequest="150" HeightRequest="150" DownsampleToViewSize="true" FadeAnimationForCachedImages="True" FadeAnimationDuration="100">
            </FFImageLoading:CachedImage>
        </Grid>

        <ScrollView Grid.Row="2">
            <StackLayout>
                <Label Text="Name:" HorizontalOptions="Center" VerticalOptions="CenterAndExpand" />
                <Label x:Name="LabelName" HorizontalOptions="Center" VerticalOptions="CenterAndExpand" />
            <Button Text="Get" Clicked="Button_Clicked" />
        </StackLayout>
        </ScrollView>
    </Grid>
</ContentPage>

MainPage.xaml.cs:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;
using System.Net;
using System.Net.Http;
using System.Web;
using Newtonsoft.Json;
using System.Xml;
using Xamarin.Essentials;
using Microsoft.AppCenter;
using Microsoft.AppCenter.Analytics;
using Microsoft.AppCenter.Crashes;
using Newtonsoft.Json.Linq;

namespace Samana
{
    public partial class MainPage : ContentPage
    {
        private string api_key = "1f02b0d8e182b5c9e9951627aa372b23";

        public MainPage()
        {
            InitializeComponent();

            NavigationPage.SetHasNavigationBar(this, false);
        }

        protected override async void OnAppearing()
        {
            base.OnAppearing();

            var location_data = await GetLocation();

            await DisplayAlert("feature_name", location_data.feature_name, "OK");
            await DisplayAlert("admin_area", location_data.admin_area, "OK");
            await DisplayAlert("locality", location_data.locality, "OK");
            await DisplayAlert("thoroughfare", location_data.thoroughfare, "OK");

            string url = "https://samples.openweathermap.org/data/2.5/weather?lat=" + location_data.latitude + "&lon=" + location_data.longitude + "&appid=" + api_key;

            using (WebClient web_client = new WebClient())
            {
                var json = web_client.DownloadString(url);

                var result = JsonConvert.DeserializeObject<WeatherInfo.Root>(json);

                WeatherInfo.Root outPut = result;

                ImageWeatherIcon.Source = string.Format("https://samana.softnames.com/icons/{0}.png", outPut.weather[0].icon);
                LabelTemprature.Text = string.Format("{0}", ToCelsius(outPut.main.temp));
                LabelDescription.Text = string.Format("{0}", outPut.weather[0].description);

                LabelName.Text = string.Format("{0}", outPut.name);
            }
        }

        private double ToCelsius(double kelvin)
        {
            double celsius;

            celsius = (kelvin - 273.15);

            return celsius;
        }

        public class LocationInfo
        {
            public double? latitude { get; set; }
            public double? longitude { get; set; }
            public string admin_area { get; set; }
            public string country_code { get; set; }
            public string country_name { get; set; }
            public string feature_name { get; set; }
            public string locality { get; set; }
            public string postal_code { get; set; }
            public string sub_admin_area { get; set; }
            public string sub_locality { get; set; }
            public string sub_thoroughfare { get; set; }
            public string thoroughfare { get; set; }
        }

        public async Task<LocationInfo> GetLocation()
        {
            var UserLocation = new LocationInfo();

            try
            {
                var last_known_location = await Geolocation.GetLastKnownLocationAsync();

                if (last_known_location != null)
                {
                    UserLocation.latitude = last_known_location.Latitude;
                    UserLocation.longitude = last_known_location.Longitude;
                }
                else
                {
                    var request = new GeolocationRequest(GeolocationAccuracy.Default);
                    var location = await Geolocation.GetLocationAsync(request);

                    if (location != null)
                    {
                        UserLocation.latitude = location.Latitude;
                        UserLocation.longitude = location.Longitude;

                        var placemarks = await Geocoding.GetPlacemarksAsync(location.Latitude, location.Longitude);

                        var placemark = placemarks?.FirstOrDefault();

                        if (placemark != null)
                        {
                            UserLocation.admin_area = placemark.AdminArea;
                            UserLocation.country_code = placemark.CountryCode;
                            UserLocation.country_name = placemark.CountryName;
                            UserLocation.feature_name = placemark.FeatureName;
                            UserLocation.locality = placemark.Locality;
                            UserLocation.postal_code = placemark.PostalCode;
                            UserLocation.sub_admin_area = placemark.SubAdminArea;
                            UserLocation.sub_locality = placemark.SubLocality;
                            UserLocation.sub_thoroughfare = placemark.SubThoroughfare;
                            UserLocation.thoroughfare = placemark.Thoroughfare;
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                Crashes.TrackError(ex, new Dictionary<string, string>
                {
                    { "Page", "Settings" },
                    { "Where", "GetLocation" }
                });

                UserLocation.latitude = null;
                UserLocation.longitude = null;
            }

            return UserLocation;
        }

        private async void Button_Clicked(object sender, EventArgs e)
        {
            var location_data = await GetLocation();

            string url = "https://samples.openweathermap.org/data/2.5/weather?lat=" + location_data.latitude + "&lon=" + location_data.longitude + "&appid=" + api_key;

            using (WebClient web_client = new WebClient())
            {
                var json = web_client.DownloadString(url);

                var result = JsonConvert.DeserializeObject<WeatherInfo.Root>(json);

                WeatherInfo.Root outPut = result;

                ImageWeatherIcon.Source = string.Format("https://samana.softnames.com/icons/{0}.png", outPut.weather[0].icon);
                LabelTemprature.Text = string.Format("{0}", ToCelsius(outPut.main.temp));
                LabelDescription.Text = string.Format("{0}", outPut.weather[0].description);

                LabelName.Text = string.Format("{0}", outPut.name);
            }

        }
    }
}

Thanks,
Jassim