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Posted 4 Apr 2009


, 4 Apr 2009
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FindWindow is a tool for searching windows/controls


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

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

  1. After starting the application, start dragging the bull eye 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 information about the underlying 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 use this in C#, so I 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");
    		(ApiWrapper.Window.GetParent(Window),Window) == false)
    		return Window;
    	// create a list to hold all children 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) * 
    	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 selected 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 * 
    		// Draw the rectangle around the window
    		IntPtr OldPen = ApiWrapper.Gdi.SelectObject(dc, Pen);
    		IntPtr OldBrush = ApiWrapper.Gdi.SelectObject
    			(dc, ApiWrapper.Gdi.GetStockObject
    		ApiWrapper.Gdi.Rectangle(dc, 0, 0, WindowRect.Width, 
    		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

    Shows the FindWindow dialog.
    Handles the mouse events (down - move - up) and displays the result information.

  • GdiApiWrapper.cs, WinApiWrapper.cs

    The base functions MainForm::ChildWindowFromPoint and MainForm::ShowInvertRectTracker use the base Win API extensively.
    The signatures of the Win API are listed in these files. The list of functions is not complete. I only implemented functions that I need for this tool.


  • 3rd April, 2009: Initial version


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Jörg Bausch
Software Developer (Senior) ModuleSoft
Germany Germany
This member doesn't quite have enough reputation to be able to display their biography and homepage.
Group type: Organisation (No members)

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Comments and Discussions

GeneralMy vote of 5 Pin
Paul Watt10-Oct-12 6:31
mentorPaul Watt10-Oct-12 6:31 
GeneralMy vote of 5 Pin
blueasa6-May-12 9:10
memberblueasa6-May-12 9:10 
Generalthanks and one question about detecting desktop items Pin
BillWoodruff6-Nov-09 1:21
memberBillWoodruff6-Nov-09 1:21 
GeneralRe: thanks and one question about detecting desktop items Pin
Jörg Bausch6-Nov-09 4:50
groupJörg Bausch6-Nov-09 4:50 
GeneralRe: thanks and one question about detecting desktop items [modified] Pin
BillWoodruff6-Nov-09 17:36
memberBillWoodruff6-Nov-09 17:36 
GeneralRe: thanks and one question about detecting desktop items Pin
Jörg Bausch7-Nov-09 0:22
groupJörg Bausch7-Nov-09 0:22 
GeneralWPF Pin
Siavash Mortazavi6-Apr-09 17:11
memberSiavash Mortazavi6-Apr-09 17:11 

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