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WPF 在 Windows 实现任务栏缩略图

控件名：SetIconicThumbnail

作 者：WPFDevelopersOrg - 驚鏵&赵嘉

原文链接^[1]：https://github.com/WPFDevelopersOrg/WPFDevelopers

码云链接^[2]：https://gitee.com/WPFDevelopersOrg/WPFDevelopers

• 框架支持.NET4 至 .NET8；
• Visual Studio 2022;

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）^[3]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 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 ==  || string.IsOrWhiteSpace(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 != )
 {
 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);
 }
 }
}

GitHub 源码地址^[4]

Gitee 源码地址^[5]