Run a background process to change backgroundimage of another page using timer in Xamarin.forms

Question

Hi StackOverflow Team,

I am trying to run a background process in my App. This background process should update just Background image on one of the pages in the App every 15 seconds. So far, I tried to create a timer in the App OnStart() method and update the backgroundimage of the page in the BeginInvokeOnMainThread() method but with no success. Can anyone help me with this?

My Code -

    {

        private static Stopwatch stopWatch = new Stopwatch();
        private const int defaultTimespan = 20;
        private readonly HomePage homePage;

        public App()
        {
            InitializeComponent();

            try
            {

                MainPage = new MainPage();

                homePage = new HomePage();

            }
            catch(Exception ex)
            {
                string str = ex.Message;
            }
        }

        protected override void OnStart()
        {
            if (!stopWatch.IsRunning)
            {
                stopWatch.Start();
            }

            Device.StartTimer(new TimeSpan(0, 0, 10), () =>
            {
                // Logic for logging out if the device is inactive for a period of time.

                if (stopWatch.IsRunning && stopWatch.Elapsed.Seconds >= defaultTimespan)
                {
                    //prepare to perform your data pull here as we have hit the 1 minute mark   

                    // Perform your long running operations here.

                    Device.BeginInvokeOnMainThread(() =>
                    {
                        // If you need to do anything with your UI, you need to wrap it in this.
                        //  homePage.BackgroundImageSource = "goldengate.jpg";
                        homePage.ChangeBackgroundImage();

                    });

                    stopWatch.Restart();
                }

              //  Always return true as to keep our device timer running.
                return true;
            });
        }

        protected override void OnSleep()
        {
            //stopWatch.Reset();
        }

        protected override void OnResume()
        {
            //stopWatch.Start();
        }
        //void ChangeHomePageImage()
        //{
        //    Navigation.PushAsync(new HomePage(appBackground));
        //    Navigation.RemovePage(this);
        //}


    }

MainPage - 
<MasterDetailPage 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"
             xmlns:local="clr-namespace:Excercise.Views"
             x:Class="Excercise.MainPage" IsPresented="False">

    <MasterDetailPage.Master>


        <local:MenuPage x:Name="menuPage"></local:MenuPage>


    </MasterDetailPage.Master>

    <MasterDetailPage.Detail>
        <NavigationPage>
            <x:Arguments>
        <local:HomePage x:Name="homePage"></local:HomePage>
            </x:Arguments>
        </NavigationPage>
    </MasterDetailPage.Detail>
</MasterDetailPage>

HomePage - 
 public partial class HomePage : ContentPage
    {
        private SQLiteAsyncConnection _connection;
        
        public HomePage()
        {
            InitializeComponent();
            //  BindingContext = new HomePageViewModel();
            _connection = DependencyService.Get<ISQLiteDb>().GetConnection();
            loadData("");
        }

        public HomePage(string BackgroundimgPath)
        {
            InitializeComponent();
            //  BindingContext = new HomePageViewModel();
            _connection = DependencyService.Get<ISQLiteDb>().GetConnection();
            loadData(BackgroundimgPath);
        }
        public HomePage(string City, string LocationKey, string StateID)
        {
            InitializeComponent();
            _connection = DependencyService.Get<ISQLiteDb>().GetConnection();
            // BindingContext = new HomePageViewModel();
            try
            {
                // Method Calls
            }
            catch (Exception)
            {
                 DisplayAlert("Error", "There was an error loading this page.", "OK");
            }
        }

        protected override void OnAppearing()
        {
            this.Title = App.AppTitle;           
            this.firstStacklayout.Margin = new Thickness(0, (Application.Current.MainPage.Height * 0.25), 0, 0);
            base.OnAppearing();
        }

Answer 1

you are creating an instance of HomePage and trying to update it, but it is NOT the same instance that is being displayed in your MasterDetail

try something like this

var md = (MasterDetailPage)MainPage;
var nav = (NavigationPage)md.DetailPage;
var home = (HomePage)nav.CurrentPage;
home.ChangeBackgroundImage();

alternately, you could use MessagingCenter to send a message to HomePage requesting that it udpate