pinvoke.net: Edit: user32.GetForegroundWindow

@msdn=http://msdn2.microsoft.com/en-us/library/ms633505(VS.85).aspx
@pinvoke=http://pinvoke.net/$$$.htm

Summary: Returns a handle to the window the user is working with.

!!!!C# Signature:
        /// <summary>
        ///     Retrieves a handle to the foreground window (the window with which the user is currently working). The system
        ///     assigns a slightly higher priority to the thread that creates the foreground window than it does to other threads.
        ///     <para>See https://msdn.microsoft.com/en-us/library/windows/desktop/ms633505%28v=vs.85%29.aspx for more information.</para>
        /// </summary>
        /// <returns>
        ///     C++ ( Type: Type: HWND )<br /> The return value is a handle to the foreground window. The foreground window
        ///     can be NULL in certain circumstances, such as when a window is losing activation.
        /// </returns>
 [DllImport("user32.dll")]
 private static extern IntPtr GetForegroundWindow();

!!!!VB.NET Signature:
 ''' <summary>The GetForegroundWindow function returns a handle to the foreground window.</summary>
 ''' <returns>The return value is a handle to the foreground window. The foreground window can be NULL in certain circumstances, such as when a window is losing activation. </returns>
 <DllImport("user32.dll", SetLastError:=True)> _
 Private Shared Function GetForegroundWindow() As IntPtr
 End Function

!!!!VB.NET Signature Alternative
 ''' <summary>
 ''' Retrieves a handle to the foreground window (the window with which the user is currently working). The system assigns a slightly higher priority to the thread that creates the foreground window than it does to other threads. 
 ''' </summary>
 ''' <returns>The return value is a handle to the foreground window. The foreground window can be NULL in certain circumstances, such as when a window is losing activation. </returns>
 ''' <remarks>http://msdn.microsoft.com/en-us/library/ms633505%28v=vs.85%29.aspx</remarks>
 Private Declare Function GetForegroundWindow Lib "user32.dll" () As IntPtr
        
!!!!VB Signature:
 Public Declare Function GetForegroundWindow Lib "user32" () As Long

!!!!F# Signature
 [<DllImport("user32")>]
 extern IntPtr GetForegroundWindow()

!!!!User-Defined Types:
None.

!!!!Notes:
None.

!!!!Tips & Tricks:
Please add some!

!!!!Sample Code:

public ApplicationState AppState
 {
 	get
 	{
 		Process[] processCollection = Process.GetProcessesByName(ProcessName);
 		if(processCollection != null && processCollection.Length  >= 1 && 
 			processCollection[0] != null)
 		{
 			IntPtr activeWindowHandle = Win32.GetForegroundWindow();
			//Optional int ProcessID;
			//Optional Win32.GetWindowThreadProcessId(GetForegroundWindow(),out ProcessID)
 			foreach(Process wordProcess in processCollection)
 			{
				//Optional if( ProcessID == wordProcess.Id ) return ApplicationState.Focused;
 				if(wordProcess.MainWindowHandle == activeWindowHandle)
 				{
 					return ApplicationState.Focused;
 				}
 			}
 			return ApplicationState.Running;
 		}
 		return ApplicationState.NotRunning;
 	}
 }

!!!!Alternative Managed API:
The ManagedWindowsApi project (http://mwinapi.sourceforge.net) provides a static property ManagedWinapi.SystemWindow.ForegroundWindow.

Documentation: GetForegroundWindow@msdn on MSDN