Background Service run continuously in Xamarin Forms

Question

i'm new with xamarin forms. I'm writing an app and i need to create a function that allow call api continuously to check the change of data, if have any change, i will handle something. I'm looking for the solution but nothing, please help me :( Thread is an idea?

Answer 1

You can use Timer Class for you issue.

Answer 2

Okay so first of all you need to poll the API in order to receive the data that you need to check. To do this you can implement my PollingTimer.cs class:

using System;
using System.Threading;
using Xamarin.Forms;

namespace CryptoTracker.Helpers
{
    /// <summary>
    /// This timer is used to poll the middleware for new information.
    /// </summary>
    public class PollingTimer
    {
        private readonly TimeSpan timespan;
        private readonly Action callback;

        private CancellationTokenSource cancellation;

        /// <summary>
        /// Initializes a new instance of the <see cref="T:CryptoTracker.Helpers.PollingTimer"/> class.
        /// </summary>
        /// <param name="timespan">The amount of time between each call</param>
        /// <param name="callback">The callback procedure.</param>
        public PollingTimer(TimeSpan timespan, Action callback)
        {
            this.timespan = timespan;
            this.callback = callback;
            this.cancellation = new CancellationTokenSource();
        }

        /// <summary>
        /// Starts the timer.
        /// </summary>
        public void Start()
        {
            CancellationTokenSource cts = this.cancellation; // safe copy
            Device.StartTimer(this.timespan,
                () => {
                    if (cts.IsCancellationRequested) return false;
                    this.callback.Invoke();
                    return true; // or true for periodic behavior
            });
        }

        /// <summary>
        /// Stops the timer.
        /// </summary>
        public void Stop()
        {
            Interlocked.Exchange(ref this.cancellation, new CancellationTokenSource()).Cancel();
        }
    }
}

Now that you have added a polling timer to your project, you must now go to the content page that you wish to poll from. Here is the pseudo code for what your content page should look like:

namespace YourApp.Views
{
    public class MainPage : ContentPage
    {

        PollingTimer timer;
        public MainPage ()
        {
            //PUT UI CODE HERE

            Content = layout;
            //Instantiate Polling timer to call handleaction every 5 seconds
            timer = new PollingTimer(TimeSpan.FromSeconds(5), HandleAction);

        }


        /// <summary>
        /// When the page enters the users view, this procedure is called.
        /// </summary>
        protected override void OnAppearing()
        {
            base.OnAppearing();
            //Handle action and start your timer
            HandleAction();
            timer.Start();
        }

        /// <summary>
        /// When the page disappears from the users view this procedure is called.
        /// </summary>
        protected override void OnDisappearing()
        {
            base.OnDisappearing();
            //Stop your timer
            timer.Stop(); //Stop the timer
        }


        /// <summary>
        /// Callback for the timer.
        /// </summary>
        void HandleAction()
        {
            //Make call to your api to get data
            //Compare data with data you currently have
            // Do whatever you want.
        }

I hope this helps you. Let me know if you need any more help :)