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 
href="https://github.com/Codefinity-Java/MAUIThreadingTask"
target="_blank"
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onmouseout="this.style.color='#d27204'">Github Repository</a>. Clone the repository to begin solving the task.

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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 diesem Kurs werden wir einige fortgeschrittene C#-Konzepte zusammen mit MAUI kennenlernen, einer Bibliothek für die Anwendungsentwicklung. Wir werden lernen, wie man interessante GUI-Anwendungen erstellt, die schnell und reaktionsfähig bleiben, indem wir Techniken wie Threading verwenden. Wir werden Anwendungen erstellen, die mit Benutzereingaben und APIs interagieren, und darüber hinaus werden wir einige wichtige C#-Konzepte wie Reflection und Generics behandeln. Dieser Kurs wird unsere Programmierfähigkeiten weiter verbessern und uns eine starke Grundlage geben, um in Richtung Webentwicklung voranzukommen.

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.

Aufgabe - Vermeidung von Programmabstürzen Durch Threading

Aufgabenbeschreibung