FindWindow: Finding Window Handles


There are many programs on the market like Spy++ or screen capture programs which allow you to find and select a specific window or window-control like Button, Edit, or others.

The goal for this project was to write an easy interface for finding window handles.

1. After starting the application, drag the bullseye symbol "Finder Tool" (1)
2. Move the "Finder Tool" Symbol to the desired window
3. Stop moving and drop the mouse cursor if you want informations about the underlaying window
4. The information about the selected window is shown in the dialog properties (2)


I have programmed such a finder tool for many years in C++. Now I used this in C#, so I have converted my old C++ code into C# code.

Using the Code

There are two important methods which find and select the window.

1. Function "MainForm::ChildWindowFromPoint"
Param: point is the global point on the screen (normally the mouse cursor)
Return: handle from the found window

static IntPtr ChildWindowFromPoint(Point point)
	IntPtr WindowPoint = ApiWrapper.Window.WindowFromPoint(point);
	if (WindowPoint == IntPtr.Zero)
		return IntPtr.Zero;

	if (ApiWrapper.Window.ScreenToClient(WindowPoint, ref point) == false)
		throw new Exception("ScreenToClient failed");

	IntPtr Window = ApiWrapper.Window.ChildWindowFromPointEx(WindowPoint, point, 0);
	if (Window == IntPtr.Zero)
		return WindowPoint;

	if(ApiWrapper.Window.ClientToScreen(WindowPoint, ref point) == false)
		throw new Exception("ClientToScreen failed");

	if(ApiWrapper.Window.IsChild(ApiWrapper.Window.GetParent(Window),Window) == false) 
		return Window;

	// create a list to hold all childs under the point
	ArrayList WindowList = new ArrayList();
	while (Window != IntPtr.Zero)
		Rectangle rect = ApiWrapper.Window.GetWindowRect(Window);
		Window = ApiWrapper.Window.GetWindow(Window, (uint)ApiWrapper.Window.GetWindow_Cmd.GW_HWNDNEXT);

	// search for the smallest window in the list
int MinPixel = GetSystemMetrics((int)GetSystem_Metrics.SM_CXFULLSCREEN) * GetSystemMetrics((int)GetSystem_Metrics.SM_CYFULLSCREEN);
	for (int i = 0; i < WindowList.Count; ++i)
		Rectangle rect = ApiWrapper.Window.GetWindowRect( (IntPtr)WindowList[i] );
		int ChildPixel = rect.Width * rect.Height;
		if (ChildPixel < MinPixel)
			MinPixel = ChildPixel;
			Window = (IntPtr)WindowList[i];
	return Window;

2. Function "MainForm::ShowInvertRectTracker"
Param: window to show/hide the select rectangle

static void ShowInvertRectTracker(IntPtr window)
	if(window != IntPtr.Zero)
		// get the coordinates from the window on the screen
		Rectangle WindowRect = ApiWrapper.Window.GetWindowRect(window);
		// get the window's device context
		IntPtr dc = ApiWrapper.Window.GetWindowDC(window);

		// Create an inverse pen that is the size of the window border
		ApiWrapper.Gdi.SetROP2(dc, (int)ApiWrapper.Gdi.RopMode.R2_NOT);

		Color color = Color.FromArgb(0, 255, 0);
		IntPtr Pen = ApiWrapper.Gdi.CreatePen((int)ApiWrapper.Gdi.PenStyles.PS_INSIDEFRAME, 3 * GetSystemMetrics((int)GetSystem_Metrics.SM_CXBORDER), (uint)color.ToArgb());

		// Draw the rectangle around the window
		IntPtr OldPen = ApiWrapper.Gdi.SelectObject(dc, Pen);
		IntPtr OldBrush = ApiWrapper.Gdi.SelectObject(dc, ApiWrapper.Gdi.GetStockObject((int)ApiWrapper.Gdi.StockObjects.NULL_BRUSH));
		ApiWrapper.Gdi.Rectangle(dc, 0, 0, WindowRect.Width, WindowRect.Height);

		ApiWrapper.Gdi.SelectObject(dc, OldBrush);
		ApiWrapper.Gdi.SelectObject(dc, OldPen);

		//release the device context, and destroy the pen
		ApiWrapper.Window.ReleaseDC(window, dc);


  • MainForm.cs
    Show the FindWindow dialog.
    Handles the mouse events (down - move - up) and display the result informations.
  • GdiApiWrapper.cs, WinApiWrapper.cs
    The base functions "MainForm::ChildWindowFromPoint" and "MainForm::ShowInvertRectTracker" use extensive the base Win Api.
    The signature's of the Win API are listed in this files. The list of functions are not complete. I only implemented the functions that I needed for this tool.

About the Author

Joerg Bausch

My name is Joerg Bausch. Currently I am a freelancer/consultant in Germany. I have been developing professionally since 1994. In the past i have worked as a programmer and projectleader. My favorite language is C++ but in the last years i developed more and more C# applications. I am interested in new technologies and look for new projects. Visit my site:



  • There are no comments yet. Be the first to comment!

Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • Anthony Christie, the Chief Marketing Officer for Level Communications, is responsible for customer experience, worldwide marketing and product management. In this informative asset, he shares his insights into why a private network connection to cloud-bases applications is the right decision for your enterprise. Download now to find out more.

  • Enterprises are increasingly looking to platform as a service (PaaS) to lower their costs and speed their time to market for new applications. Developing, deploying, and managing applications in the cloud eliminates the time and expense of managing a physical infrastructure to support them. PaaS offerings must deliver additional long-term benefits, such as a lower total cost of ownership (TCO), rapid scalability, and ease of integration, all while providing robust security and availability. This report …

Most Popular Programming Stories

More for Developers

RSS Feeds

Thanks for your registration, follow us on our social networks to keep up-to-date