Switch Foreground window event capture [success in C#]

Here is the source code:

using System;

using System.Collections.Generic;

using System.Windows.Forms;

using System.Runtime.InteropServices;

using System.Text;

namespace ExampleApp

{

class ExampleForm : Form

{

delegate void WinEventDelegate(IntPtr hWinEventHook,

uint eventType, IntPtr hwnd, int idObject,

int idChild, uint dwEventThread, uint dwmsEventTime);

const uint WINEVENT_OUTOFCONTEXT = 0;

const uint EVENT_SYSTEM_FOREGROUND = 3;

[DllImport("user32.dll")]

static extern bool UnhookWinEvent(IntPtr hWinEventHook);

[DllImport("user32.dll")]

static extern IntPtr SetWinEventHook(uint eventMin,

uint eventMax, IntPtr hmodWinEventProc,

WinEventDelegate lpfnWinEventProc, uint idProcess,

uint idThread, uint dwFlags);

[DllImport("user32.dll")]

static extern int GetWindowText(IntPtr hWnd,

StringBuilder lpString, int nMaxCount);

[STAThread]

static void Main()

{

Application.EnableVisualStyles();

Application.SetCompatibleTextRenderingDefault(false);

Application.Run(new ExampleForm());

}

ListBox m_list;

IntPtr m_hhook;

public ExampleForm()

{

m_list = new ListBox();

m_list.IntegralHeight = false;

m_list.Dock = DockStyle.Fill;

Controls.Add(m_list);

Text = "SetWinEventHook Example";

Load += new EventHandler(Program_Load);

FormClosing +=

new FormClosingEventHandler(Program_FormClosing);

}

void Program_Load(object sender, EventArgs e)

{

m_hhook = SetWinEventHook(EVENT_SYSTEM_FOREGROUND,

EVENT_SYSTEM_FOREGROUND, IntPtr.Zero,

WinEventProc, 0, 0, WINEVENT_OUTOFCONTEXT);

}

void WinEventProc(IntPtr hWinEventHook, uint eventType,

IntPtr hwnd, int idObject, int idChild,

uint dwEventThread, uint dwmsEventTime)

{

if (eventType == EVENT_SYSTEM_FOREGROUND)

{

StringBuilder sb = new StringBuilder(500);

GetWindowText(hwnd, sb, sb.Capacity);

m_list.Items.Insert(0,

"Switched to: " + sb.ToString());

}

}

void Program_FormClosing(

object sender, FormClosingEventArgs e)

{

UnhookWinEvent(m_hhook);

}

}

}

source: http://social.msdn.microsoft.com/Forums/en/clr/thread/c04e343f-f2e7-469a-8a54-48ca84f78c28 (may also refer to msdn library for the theory)