MainWindow.xaml.cs

using FluentDL.Helpers;
using Windows.UI.ViewManagement;
using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Controls;
using Microsoft.UI.Xaml.Controls.Primitives;
using Microsoft.UI.Xaml.Data;
using Microsoft.UI.Xaml.Input;
using Microsoft.UI.Xaml.Media;
using Microsoft.UI.Xaml.Navigation;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using Windows.Foundation;
using Windows.Foundation.Collections;
using RestSharp;
using System.Text.Json;
using Microsoft.UI.Composition.SystemBackdrops;
using System.Runtime.InteropServices; // For DllImport
using WinRT; // required to support Window.As<ICompositionSupportsSystemBackdrop>()
using Microsoft.UI.Windowing;
using Microsoft.UI;
using WinRT.Interop;
using Windows.UI;


namespace FluentDL;

public sealed partial class MainWindow : WindowEx
{
    private Microsoft.UI.Dispatching.DispatcherQueue dispatcherQueue;

    private UISettings settings;

    public MainWindow()
    {
        InitializeComponent();

        AppWindow.SetIcon(Path.Combine(AppContext.BaseDirectory, "Assets/WindowIcon.ico"));
        Content = null;
        Title = "AppDisplayName".GetLocalized();

        // Theme change code picked from https://github.com/microsoft/WinUI-Gallery/pull/1239
        dispatcherQueue = Microsoft.UI.Dispatching.DispatcherQueue.GetForCurrentThread();
        settings = new UISettings();
        settings.ColorValuesChanged += Settings_ColorValuesChanged; // cannot use FrameworkElement.ActualThemeChanged event
    }

    // this handles updating the caption button colors correctly when indows system theme is changed
    // while the app is open
    private void Settings_ColorValuesChanged(UISettings sender, object args)
    {
        // This calls comes off-thread, hence we will need to dispatch it to current app's thread
        dispatcherQueue.TryEnqueue(() =>
        {
            TitleBarHelper.ApplySystemThemeToCaptionButtons();
        });
    }
}