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。

    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

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

截图方法及详细操作如下：

    private BitmapImage GetWindowShotCut(IntPtr intPtr)
    {
        var image = WindowCaptureHelper.GetShotCutImage(intPtr);
        var bitmapImage = BitmapConveters.ConvertToBitmapImage(image);
        return bitmapImage;
    }

WindowCaptureHelper：

    public class WindowCaptureHelper
    {
        [DllImport("user32.dll")]
        private static extern IntPtr GetWindowRect(IntPtr hWnd, ref Rectangle rect);
        [DllImport("gdi32.dll")]
        private static extern IntPtr CreateCompatibleDC(IntPtr hdc);
        [DllImport("gdi32.dll")]
        private static extern IntPtr CreateCompatibleBitmap(IntPtr hdc, int nWidth, int nHeight);
        [DllImport("gdi32.dll")]
        private static extern IntPtr SelectObject(IntPtr hdc, IntPtr hgdiobj);
        [DllImport("gdi32.dll")]
        private static extern int DeleteDC(IntPtr hdc);
        [DllImport("user32.dll")]
        private static extern bool PrintWindow(IntPtr hwnd, IntPtr hdcBlt, int nFlags);
        [DllImport("user32.dll")]
        private static extern IntPtr GetWindowDC(IntPtr hwnd);

        public static Bitmap GetShotCutImage(IntPtr hWnd)
        {
            var hscrdc = GetWindowDC(hWnd);
            var windowRect = new Rectangle();
            GetWindowRect(hWnd, ref windowRect);
            int width = Math.Abs(windowRect.Width- windowRect.X);
            int height = Math.Abs(windowRect.Height- windowRect.Y);
            var hbitmap = CreateCompatibleBitmap(hscrdc, width, height);
            var hmemdc = CreateCompatibleDC(hscrdc);
            SelectObject(hmemdc, hbitmap);
            PrintWindow(hWnd, hmemdc, 0);
            var bmp = Image.FromHbitmap(hbitmap);
            DeleteDC(hscrdc);
            DeleteDC(hmemdc);
            return bmp;
        }
    }

BitmapConveters：

    public class BitmapConveters
    {
        [DllImport("gdi32")]
        static extern int DeleteObject(IntPtr o);
        public static BitmapSource ConvertToBitMapSource(Bitmap bitmap)
        {
            IntPtr intPtrl = bitmap.GetHbitmap();
            BitmapSource bitmapSource = System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(intPtrl,
                IntPtr.Zero,
                Int32Rect.Empty,
                BitmapSizeOptions.FromEmptyOptions());
            DeleteObject(intPtrl);
            return bitmapSource;
        }
        public static BitmapImage ConvertToBitmapImage(Bitmap bitmap)
        {
            using (MemoryStream stream = new MemoryStream())
            {
                bitmap.Save(stream, ImageFormat.Bmp);
                stream.Position = 0;
                BitmapImage result = new BitmapImage();
                result.BeginInit();
                result.CacheOption = BitmapCacheOption.OnLoad;
                result.StreamSource = stream;
                result.EndInit();
                result.Freeze();
                return result;
            }
        }
    }

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)