winforms - Send Keystrokes to a program even if its in background using c#

Question

I wanna send key stroke to a program even if it is running in background. But I can do this only for NOTEPAD like this,

[DllImport("user32.dll")]
protected static extern byte VkKeyScan(char ch);

[DllImport("user32.dll", SetLastError = true)]
protected static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpszClass, string lpszWindow);

[DllImport("User32.Dll", EntryPoint = "PostMessageA")]
protected static extern bool PostMessage(IntPtr hWnd, uint msg, int wParam, int lParam);

---

char Key = // key value to send

IntPtr hWnd = FindWindowEx(_handle, IntPtr.Zero, "edit", null);   // _handle is the windows handle of the program (here its notepad)
PostMessage(hWnd, WM_KEYDOWN, VkKeyScan(Key), 0);

But for all other applications I can't send keystrokes if its in background. Since I don't know the lpszClass of that program (I think this is the userControl name of the typing area in that program. For NotePad it is "edit". I found this surfing internet).

For all other applications what I'm doing is, get the application to foreground, then send the key, then again get my program foreground. I need my program to be run as foreground always.

[DllImport("USER32.DLL")]
public static extern bool SetForegroundWindow(IntPtr hWnd);

---

SetForegroundWindow(_handle);       // _handle is the windows handle of the program

System.Threading.Thread.Sleep(50);       // Waiting few milliseconds till application coming to foreground.                    
wsh.SendKeys(Key.ToString(), ref wait);  // wsh is WshShellClass wsh= new WshShellClass();
SetForegroundWindow(_mainHandle);    // _mainHandle is the windows handle of my application

But this way is not working. some keys getting missed and the program foreground->background->foregound->background...... like its dancing...

How to send keys to other applications if its running in background. or are there any way/source to find the lpszClass of a program ?

Sorry if I have missed any required information. this is a large application. I have posted only required parts here. If someone needs any additional information, pls ask.

Answer 1

I think you'll need to have the background program install a low-level keyboard hook via the win32 function SetWindowsHookEx().

Here's the MSDN documentation for SetWindowsHookEX()

http://msdn.microsoft.com/en-us/library/ms644990(v=vs.85).aspx

And here's the KB article on how to do it from C#

http://support.microsoft.com/kb/318804

This article goes into some detail, too: http://www.codeguru.com/columns/vb/article.php/c4829

I expect your app will get caught by various spyware/anti-virus software as a keyboard logger, though.

Good luck.