在 Windows Vista 系统上，微软首次推出任务栏缩略图预览功能。Windows 任务栏中，当我们将窗口最小化并将鼠标悬停在图标上，会显示一个窗口预览缩略图。通过 Windows DWM（Desktop Window Manager）提供的 API，我们可以自定义这个缩略图的内容，实现类似音乐播放器当前播放的音乐封面图。

1. 修改 WindowHelpers.cs
.先检查 window 是否为 null 或 imagePath 是否为空。
.使用 WindowInteropHelper 获取 window 的句柄 (hwnd);
.注册窗口消息钩子，监听 DWM 消息；
.window.ShowInTaskbar = true;设置 Window 有任务栏图标，否则无法显示预览缩略图。

public static void SetIconicThumbnail(this Window window, string imagePath)
{
    if (window == null || string.IsNullOrWhiteSpace(imagePath)) return;
    if (!File.Exists(imagePath)) return;
    IntPtr hwnd = new WindowInteropHelper(window).Handle;
    int size = Marshal.SizeOf(typeof(int));
    IntPtr pBool = Marshal.AllocHGlobal(size);
    try
    {
        Marshal.WriteInt32(pBool, 1);
        Win32.DwmSetWindowAttribute(hwnd, DwmWindowAttributes.FORCE_ICONIC_REPRESENTATION, pBool, size);
        Win32.DwmSetWindowAttribute(hwnd, DwmWindowAttributes.HAS_ICONIC_BITMAP, pBool, size);
    }
    finally
    {
        Marshal.FreeHGlobal(pBool);
    }
    var source = HwndSource.FromHwnd(hwnd);
    if (source != null)
    {
        source.AddHook(new HwndSourceHook((IntPtr hwnd2, int msg, IntPtr wParam, IntPtr lParam, refbool handled) =>
        {
            if (msg == WindowsMessageCodes.WM_DWMSENDICONICTHUMBNAIL)
            {
                int width = ((int)((((long)lParam) >> 16) & 0xFFFF));
                int height = ((int)((long)lParam & 0xFFFF));
                try
                {
                    using (var bmp = new Bitmap(imagePath))
                    using (var resized = new Bitmap(bmp, new Size(width, height)))
                    {
                        IntPtr hBitmap = resized.GetHbitmap();
                        Win32.DwmSetIconicThumbnail(hwnd2, hBitmap, (int)DwmWindowAttributes.None);
                        Win32.DeleteObject(hBitmap);
                    }
                }
                catch (Exception ex)
                {
                    thrownew Exception($"DwmSetIconicThumbnail error :{ex.Message}!");
                }
                handled = true;
            }

            return IntPtr.Zero;
        }));
    }
    Win32.DwmInvalidateIconicBitmaps(hwnd);
    window.ShowInTaskbar = true;
}

2. 修改 Win32.cs
.DwmSetWindowAttribute 设置打开缩略图显示图片；
.DwmSetIconicThumbnail 设置自定义缩略图给任务栏；
.DwmInvalidateIconicBitmaps 通知 DWM 当前的缩略图无效，重新请求；
.WM_DWMSENDICONICTHUMBNAILDWM 向窗口发送消息，请求新的缩略图；
.DeleteObject() 手动释放 GDI ，避免内存泄漏；

[DllImport(Gdi32)]
public static extern bool DeleteObject(IntPtr hObject);
[DllImport(DwmApi)]
public static extern int DwmSetIconicThumbnail(IntPtr hwnd, IntPtr hbmp, int dwSITFlags);
[DllImport(DwmApi)]
public static extern int DwmSetWindowAttribute(IntPtr hwnd, DwmWindowAttributes dwAttribute, IntPtr pvAttribute, int cbAttribute);
[DllImport(DwmApi)]
public static extern int DwmInvalidateIconicBitmaps(IntPtr hwnd);

internalclassWindowsMessageCodes
{
    publicconstint WM_DWMSENDICONICTHUMBNAIL = 0x0323;
}
[Flags]
publicenum DwmWindowAttributes : uint
{
    None = 0, 
    DISPLAYFRAME = 1,
    FORCE_ICONIC_REPRESENTATION = 7,
    HAS_ICONIC_BITMAP = 10
}

3. 新增 IconicThumbnailWindowExample.xaml
.新增两个按钮切换图片，BtnPrevious_Click 和 BtnNext_Click。
.Image 控件用于显示任务栏的缩略图。

<wd:Window
    x:Class="WPFDevelopers.Sample.ExampleViews.IconicThumbnailWindowExample"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:converts="clr-namespace:WPFDevelopers.Sample.Converts"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:local="clr-namespace:WPFDevelopers.Sample.ExampleViews"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:model="clr-namespace:WPFDevelopers.Sample.Models"
    xmlns:wd="https://github.com/WPFDevelopersOrg/WPFDevelopers"
    Title="IconicThumbnailWindowExample"
    Width="600"
    Height="450"
    Icon="pack://application:,,,/WPFDevelopers.Samples;component/WPFDevelopers.ico"
    WindowStartupLocation="CenterScreen"
    mc:Ignorable="d">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="7*" />
            <RowDefinition Height="3*" />
        </Grid.RowDefinitions>
        <Image
            x:Name="ImagePreview"
            Width="200"
            Height="200"
            VerticalAlignment="Bottom" />
        <StackPanel
            Grid.Row="1"
            HorizontalAlignment="Center"
            VerticalAlignment="Center"
            wd:PanelHelper.Spacing="3"
            Orientation="Horizontal">
            <Button
                x:Name="BtnPrevious"
                Width="50"
                Height="50"
                Click="BtnPrevious_Click">
                <wd:PathIcon Width="10" Kind="Previous" />
            </Button>
            <Button
                x:Name="BtnNext"
                Width="50"
                Height="50"
                Click="BtnNext_Click">
                <wd:PathIcon Width="10" Kind="Next" />
            </Button>
        </StackPanel>
    </Grid>
</wd:Window>

4. 新增 IconicThumbnailWindowExample.xaml.cs
BtnNext_ClickcurrentFileIndex = (currentFileIndex + 1) % fileList.Count; 通过代码实现图片循环切换：每次点击按钮时，currentFileIndex 会增加 1，如果超过了 fileList 的最大索引，回到第一个图片。
BtnPrevious_ClickcurrentFileIndex = (currentFileIndex - 1 + fileList.Count) % fileList.Count; 通过代码实现图片循环切换：每次点击按钮时，currentFileIndex 会减少 1，并且如果当前索引小于 0，回到最后一张图片。

using System;
using System.Collections.Generic;
using System.IO;
using System.Windows;
using System.Windows.Media.Imaging;
using WPFDevelopers.Helpers;

namespaceWPFDevelopers.Sample.ExampleViews
{
    /// <summary>
    /// IconicThumbnailWindowExample.xaml 的交互逻辑
    /// </summary>
    publicpartialclassIconicThumbnailWindowExample
    {
        private List<string> fileList = new List<string>(); 
        privateint currentFileIndex = -1;
        public IconicThumbnailWindowExample()
        {
            InitializeComponent();
            Loaded += IconicThumbnailWindowExample_Loaded;
        }

        private void IconicThumbnailWindowExample_Loaded(object sender, RoutedEventArgs e)
        {
            fileList.Clear();
            currentFileIndex = -1;
            var directorys = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "IconicThumbnail");
            if (!Directory.Exists(directorys)) return;
            string[] files = Directory.GetFiles(directorys);
            fileList.AddRange(files);
        }

        private void BtnPrevious_Click(object sender, RoutedEventArgs e)
        {
            if (fileList.Count == 0) return;
            currentFileIndex = (currentFileIndex + 1) % fileList.Count;
            var img = fileList[currentFileIndex];
            ImagePreview.Source = new BitmapImage(new Uri(img));
            this.SetIconicThumbnail(img);
        }
        private void BtnNext_Click(object sender, RoutedEventArgs e)
        {
            if (fileList.Count == 0) return;
            currentFileIndex = (currentFileIndex - 1 + fileList.Count) % fileList.Count;
            var img = fileList[currentFileIndex];
            ImagePreview.Source = new BitmapImage(new Uri(img));
            this.SetIconicThumbnail(img);
        }
    }
}

参考资料：

[1] Windows DWM（Desktop Window Manager）: https://learn.microsoft.com/zh-cn/windows/win32/dwm/dwm-overview?redirectedfrom=MSDN
[2] GitHub 源码地址: https://github.com/WPFDevelopersOrg/WPFDevelopers/blob/dev/src/WPFDevelopers.Shared/Core/Helpers/WindowHelpers.cs
[3] Gitee 源码地址: https://gitee.com/WPFDevelopersOrg/WPFDevelopers/blob/dev/src/WPFDevelopers.Shared/Core/Helpers/WindowHelpers.cs