Summary  
This chapter covers moving blocking operations to background threads and marshaling updates back to the main thread to prevent UI freezes.

General domain of usage  
Responsive GUI applications

The base program is given on the <a 
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  Statements related to UI updates are best to execute in the Main Thread.
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<div id="solution-block" class="block">
  <pre><code class="language-csharp">
using Microsoft.Maui.Controls.Shapes;
using System.Globalization;
using System.Net.Http;

namespace MauiApp1
{
    public class apiEvent
    {
        public delegate void apiEventHandler(object sender, apiEventArgs e);

        public event apiEventHandler? OnResponse;

        public void OnApiResponse(string content)
        {
            apiEventHandler? handler = OnResponse;

            if (handler != null)
            {
                handler(this, new apiEventArgs(content));
            }
        }
    }

    public class apiEventArgs : EventArgs
    {
        public string Link { get; }

        public apiEventArgs(string content)
        {
            this.Link = content;
        }
    }

    public partial class MainPage : ContentPage
    {
        public apiEvent apiService = new apiEvent();

        Thread? mainTimer;
        Thread? getRequestThread;
        long ticks;

        public MainPage()
        {
            InitializeComponent();

            getImageButton.Clicked += GetImage;
            apiService.OnResponse += SetImage;

            ticks = 0;
            mainTimer = new Thread(new ThreadStart(timerUpdate));
            mainTimer.Start();
        }

        public void timerUpdate()
        {
            while (true)
            {
                ticks++;
                Thread.Sleep(50);
                MainThread.BeginInvokeOnMainThread(() => {
                    timerLabel.Text = $"Tick Count: {ticks}";
                });
            }
        }

        private void SetImage(object? sender, apiEventArgs e)
        {
            MainThread.BeginInvokeOnMainThread(() =>
            {
                mainImage.Source = e.Link;
            });
        }

        private void GetImage(object? sender, EventArgs e)
        {
            if (getRequestThread != null && !getRequestThread.IsAlive)
                getRequestThread = null;

            if (getRequestThread == null)
            {
                getRequestThread = new Thread(new ThreadStart(GetRequest));
                getRequestThread.Start();
            }
        }

        private void GetRequest()
        {
            string apiUrl = "https://random.imagecdn.app/v1/image";

            using (HttpClient client = new HttpClient())
            {
                HttpResponseMessage response = client.GetAsync(apiUrl).Result;

                if (response.IsSuccessStatusCode)
                {
                    string content = response.Content.ReadAsStringAsync().Result;
                    apiService.OnApiResponse(content);
                }
            }
        }
    }
}    
      </code></pre>
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In this course, we will learn about some advanced C# concepts along with MAUI, which is an application development library. We will learn how to create some interesting GUI applications while keeping them quick and responsive using techniques like Threading. We will make applications that will interact user input and APIs, and apart from that, we will cover some important C# concepts like Reflection and Generics. This course will further improve our programming skills and will give us a strong foundation to move forward towards Web Development.

In this section, we will learn what MAUI is, and how to set up a .NET MAUI application. We will also look at the structure of an MAUI application, and in the end, we will learn how to add some basic elements to our UI. This section will prepare us for the rest of the course where we will be working with more practical concepts.

In this section we will learn about delegates, events and data binding. Using this knowledge we will learn how to make interesting interactive GUI applications.

In this section, we will learn what Threading is and how to use it to keep our applications responsive, and run smoothly while performing resource intensive tasks. We will see how to differs from other similar concepts on C# and what are good practices when implementing Threading in our application. There will also be some interesting tasks to help us in understand this concept on a deeper level.

In this section, we will learn how to make more robust methods, classes and other objects which can work multiple types of input data types, by first learning about Generics and how to implement generic classes, then we will move on to Reflection and how to use reflection for further improving the capabilities of our programs.

Challenge: Preventing Program Freezes Using Threading

Task Description