C# 根据窗口句柄获取窗口截图

本章介绍如何通过句柄，截取指定窗口内容，以及截取失败的场景

一、根据窗口句柄获取窗口截图

先创建一个测试窗口程序A，显示如下：

同时我们把此窗口的句柄显示到一个文本输入框内。

1     TestBox.Text = new WindowInteropHelper(this).Handle.ToString();

如上图所示，1774674是此窗口的句柄值。

然后，我们新建一个窗口程序B，对窗口A进行截图并展示

1     var windowIntPtr = new IntPtr(1774674);
2     var bitmapImage = GetWindowShotCut(windowIntPtr);
3     TestImage.Source = bitmapImage;

截图方法及详细操作如下：

1     private BitmapImage GetWindowShotCut(IntPtr intPtr)
2     {
3         var image = WindowCaptureHelper.GetShotCutImage(intPtr);
4         var bitmapImage = BitmapConveters.ConvertToBitmapImage(image);
5         return bitmapImage;
6     }

WindowCaptureHelper：

 1     public class WindowCaptureHelper
 2     {
 3         [DllImport("user32.dll")]
 4         private static extern IntPtr GetWindowRect(IntPtr hWnd, ref Rectangle rect);
 5         [DllImport("gdi32.dll")]
 6         private static extern IntPtr CreateCompatibleDC(IntPtr hdc);
 7         [DllImport("gdi32.dll")]
 8         private static extern IntPtr CreateCompatibleBitmap(IntPtr hdc, int nWidth, int nHeight);
 9         [DllImport("gdi32.dll")]
10         private static extern IntPtr SelectObject(IntPtr hdc, IntPtr hgdiobj);
11         [DllImport("gdi32.dll")]
12         private static extern int DeleteDC(IntPtr hdc);
13         [DllImport("user32.dll")]
14         private static extern bool PrintWindow(IntPtr hwnd, IntPtr hdcBlt, int nFlags);
15         [DllImport("user32.dll")]
16         private static extern IntPtr GetWindowDC(IntPtr hwnd);
17
18         public static Bitmap GetShotCutImage(IntPtr hWnd)
19         {
20             var hscrdc = GetWindowDC(hWnd);
21             var windowRect = new Rectangle();
22             GetWindowRect(hWnd, ref windowRect);
23             int width = Math.Abs(windowRect.Width- windowRect.X);
24             int height = Math.Abs(windowRect.Height- windowRect.Y);
25             var hbitmap = CreateCompatibleBitmap(hscrdc, width, height);
26             var hmemdc = CreateCompatibleDC(hscrdc);
27             SelectObject(hmemdc, hbitmap);
28             PrintWindow(hWnd, hmemdc, 0);
29             var bmp = Image.FromHbitmap(hbitmap);
30             DeleteDC(hscrdc);
31             DeleteDC(hmemdc);
32             return bmp;
33         }
34     }

BitmapConveters：

 1     public class BitmapConveters
 2     {
 3         [DllImport("gdi32")]
 4         static extern int DeleteObject(IntPtr o);
 5         public static BitmapSource ConvertToBitMapSource(Bitmap bitmap)
 6         {
 7             IntPtr intPtrl = bitmap.GetHbitmap();
 8             BitmapSource bitmapSource = System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(intPtrl,
 9                 IntPtr.Zero,
10                 Int32Rect.Empty,
11                 BitmapSizeOptions.FromEmptyOptions());
12             DeleteObject(intPtrl);
13             return bitmapSource;
14         }
15         public static BitmapImage ConvertToBitmapImage(Bitmap bitmap)
16         {
17             using (MemoryStream stream = new MemoryStream())
18             {
19                 bitmap.Save(stream, ImageFormat.Bmp);
20                 stream.Position = 0;
21                 BitmapImage result = new BitmapImage();
22                 result.BeginInit();
23                 result.CacheOption = BitmapCacheOption.OnLoad;
24                 result.StreamSource = stream;
25                 result.EndInit();
26                 result.Freeze();
27                 return result;
28             }
29         }
30     }

截图后显示如下：

二、窗口截图失败

窗口A在特定场景下，我们截到的窗口内容是黑色的：

截图获取失败了，窗口A做了什么处理？

定位发现是属性AllowsTransparency="True"的锅，搜索了下，网上也有同样的反馈：

• Taking a screenshot of windows with AllowsTransparency="True" (microsoft.com)
• c# - Capture transparent WPF Window for streaming - Stack Overflow
• .net - Transparent child window renders as black when screen sharing main window on Microsoft Teams - Stack Overflow

有个Issue在跟进：Screen capture semi-transparent windows? · Issue #334 · microsoft/WindowsCompositionSamples (github.com)

官方大佬说，这是他们的一个BUG。在win10 2004更新版本中，已处理。

不过，我现在是win11，依然还有问题。。。我是在win10上直接更新到win11，可能原来那个win10企业LTSC版本有点老，win11更新只更新了UI？或者win11是基于原来旧分支开发的？等回复中...Taking a screenshot of windows with AllowsTransparency="True" · Issue #358 · microsoft/WindowsCompositionSamples (github.com)