WindowIcon.cs

using System.IO;
using System.Windows;
using System.Windows.Interop;

namespace Parry;

internal static class WindowIcon
{
    private static System.Drawing.Icon? _small;
    private static System.Drawing.Icon? _big;

    public static void Apply(Window window)
    {
        window.SourceInitialized += (_, _) => ApplyTo(new WindowInteropHelper(window).Handle);
    }

    public static void ApplyTo(IntPtr hwnd)
    {
        Ensure();
        if (hwnd == IntPtr.Zero || _small is null || _big is null) return;
        NativeMethods.SendMessage(hwnd, NativeMethods.WM_SETICON, NativeMethods.ICON_SMALL, _small.Handle);
        NativeMethods.SendMessage(hwnd, NativeMethods.WM_SETICON, NativeMethods.ICON_BIG, _big.Handle);
    }

    private static void Ensure()
    {
        if (_big is not null) return;
        var stream = System.Windows.Application.GetResourceStream(new Uri("pack://application:,,,/Assets/parry.ico"))?.Stream;
        if (stream is null) return;
        using (stream)
        {
            var ms = new MemoryStream();
            stream.CopyTo(ms);
            var bytes = ms.ToArray();
            var sm = Math.Max(16, NativeMethods.GetSystemMetrics(NativeMethods.SM_CXSMICON));
            var lg = Math.Max(32, NativeMethods.GetSystemMetrics(NativeMethods.SM_CXICON));
            _small = new System.Drawing.Icon(new MemoryStream(bytes), sm, sm);
            _big = new System.Drawing.Icon(new MemoryStream(bytes), lg, lg);
        }
    }
}